Neurospora crassa Shear & B. O. Dodge 1927

Neurospora crassa és un tipus de fong de floridura dins la divisió Ascomycota. El nom del gènere que significa "nervi espora", fa referència a les característiques estriacions de les seves espores. La primera menció d'aquest fong va ser l'any 1843 quan va infestar fleques franceses.^[1]

N. crassa es fa servir com organisme model per la seva facilitat de creixement i perquè té un cicle vital haploide fàcil d'analitzar en genètica. El seu genoma ja ha estat seqüenciat completament.^[2][3] El seu genoma fa unes 43 megabases de llargada i inclou uns 10.000 gens.^[4]

Neurospora va ser utilitzat en els seus experiments pels Premis Nobel en fisiologia i medicina Edward Tatum i George Wells Beadle.^[5] En el medi natural, N. crassa viu sobretot en regions tropicals i subtropicals. Es pot trobar creixent en plantes mortes després d'incendis.

Neurospora es fa servir en la recerca científica a tot els món. És important per elucidar els esdeveniments moleculars implicats en els ritmes circadians, epigenètica i silenciar gens, polaritat cel·lular, fusió cel·lular, desenvolupamentt, com tambémolts aspectes de la biologia cel·lular i la bioquímica.

Notes i referències

Enllaços externs

• Neurospora crassa genome [1]
• «The Neurospora Homepage». Fungal Genetics Stock Center (FGSC). [Consulta: 27 desembre 2005].
• «The Neurospora Compendium». Fungal Genetics Stock Center (FGSC). [Consulta: 27 desembre 2005].
• «The Neurospora-Fungal Genome Initiative». Neurospora Genome Project. [Consulta: 28 desembre 2005].
• «Trans-NIH Neurospora Initiative». National Institutes of Health (NIH — United States). [Consulta: 27 desembre 2005].
• Neurospora crassa facts, life cycle, tissues, mating types
• [2] Montenegro-Montero A. (2010) "The Almighty Fungi: The Revolutionary Neurospora crassa". A historical view of the many contributions of this organism to molecular biology.

Neurospora crassa ist ein roter Schimmelpilz aus der Abteilung der Schlauchpilze (Ascomycota).

Er ist ein bekannter Modellorganismus in der Biologie, der leicht zu züchten ist. Er hat einen haplontischen Lebenszyklus, der eine einfache genetische Analyse erlaubt. Neurospora wurde von Edward Tatum und George Wells Beadle als Untersuchungsobjekt gewählt. Für ihre Arbeiten erhielten sie 1958 den Nobelpreis. Sie setzten den Schimmelpilz ionisierender Strahlung aus, um Mutationen auszulösen. Anschließend untersuchten sie die Stoffwechselwege auf Defekte in Enzymtätigkeiten. Aus ihren Beobachtungen leiteten sie die Ein-Gen-ein-Enzym-Hypothese ab, die heute allerdings nur noch eingeschränkt gültig ist.

Im April 2003 wurde in Nature das Genom von N. crassa als durchsequenziert veröffentlicht. Es ist etwa 40 Megabasen groß und enthält rund 10.000 Gene.^[1]

Systematik

N. crassa dient als Repräsentant für die Klade um das Taxon der Nucletmycea.^[2]

Einzelnachweise

1. ↑ J. E. Galagan, S. E. Calvo, K. A. Borkovich et al.: The genome sequence of the filamentous fungus Neurospora crassa. Nature, Nr. 422, 2003, S. 859–868, doi:10.1038/nature01554 (HTML Online).
2. ↑ S. M. Adl, A. G. B. Simpson, C. E. Lane, J. Lukeš, et al.: The Revised Classification of Eukaryotes. Journal of Eukaryotic Microbiology, Nr. 59(5), 2012, S. 429–493, doi:10.1111/j.1550-7408.2012.00644.x (PDF Online).

Neurospora crassa is a type of red bread mold of the phylum Ascomycota. The genus name, meaning 'nerve spore' in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestation of French bakeries in 1843.^[1]

Neurospora crassa is used as a model organism because it is easy to grow and has a haploid life cycle that makes genetic analysis simple since recessive traits will show up in the offspring. Analysis of genetic recombination is facilitated by the ordered arrangement of the products of meiosis in Neurospora ascospores. Its entire genome of seven chromosomes has been sequenced.^[2]

Neurospora was used by Edward Tatum and George Wells Beadle in their experiments for which they won the Nobel Prize in Physiology or Medicine in 1958. Beadle and Tatum exposed N. crassa to x-rays, causing mutations. They then observed failures in metabolic pathways caused by errors in specific enzymes. This led them to propose the "one gene, one enzyme" hypothesis that specific genes code for specific proteins. Their hypothesis was later elaborated to enzyme pathways by Norman Horowitz, also working on Neurospora. As Norman Horowitz reminisced in 2004,^[3] "These experiments founded the science of what Beadle and Tatum called 'biochemical genetics'. In actuality, they proved to be the opening gun in what became molecular genetics and all developments that have followed from that."

In the 24 April 2003 issue of Nature, the genome of N. crassa was reported as completely sequenced.^[4] The genome is about 43 megabases long and includes approximately 10,000 genes. There is a project underway to produce strains containing knockout mutants of every N. crassa gene.^[5]

In its natural environment, N. crassa lives mainly in tropical and sub-tropical regions.^[6] It can be found growing on dead plant matter after fires.

Neurospora is actively used in research around the world. It is important in the elucidation of molecular events involved in circadian rhythms, epigenetics and gene silencing, cell polarity, cell fusion, development, as well as many aspects of cell biology and biochemistry.

The sexual cycle

Neurospora crassa life cycle. The haploid mycelium reproduces asexually by two processes: (1) simple proliferation of existing mycelium, and (2) formation of conidia (macro- and micro-) which can be dispersed and then germinate to produce new mycelium. In the sexual cycle, mating can only occur between individual strains of different mating type, A and a. Fertilization occurs by the passage of nuclei of conidia or mycelium of one mating type into the protoperithecia of the opposite mating type through the trichogyne. Fusion of the nuclei of opposite mating types occurs within the protoperithecium to form a zygote (2N) nucleus.

Sexual fruiting bodies (perithecia) can only be formed when two mycelia of different mating type come together (see Figure). Like other Ascomycetes, N. crassa has two mating types that, in this case, are symbolized by A and a. There is no evident morphological difference between the A and a mating type strains. Both can form abundant protoperithecia, the female reproductive structure (see Figure). Protoperithecia are formed most readily in the laboratory when growth occurs on solid (agar) synthetic medium with a relatively low source of nitrogen.^[7] Nitrogen starvation appears to be necessary for expression of genes involved in sexual development.^[8] The protoperithecium consists of an ascogonium, a coiled multicellular hypha that is enclosed in a knot-like aggregation of hyphae. A branched system of slender hyphae, called the trichogyne, extends from the tip of the ascogonium projecting beyond the sheathing hyphae into the air. The sexual cycle is initiated (i.e. fertilization occurs) when a cell (usually a conidium) of opposite mating type contacts a part of the trichogyne (see Figure). Such contact can be followed by cell fusion leading to one or more nuclei from the fertilizing cell migrating down the trichogyne into the ascogonium. Since both A and a strains have the same sexual structures, neither strain can be regarded as exclusively male or female. However, as a recipient, the protoperithecium of both the A and a strains can be thought of as the female structure, and the fertilizing conidium can be thought of as the male participant.

The subsequent steps following fusion of A and a haploid cells, have been outlined by Fincham and Day^[9] and Wagner and Mitchell.^[10] After fusion of the cells, the further fusion of their nuclei is delayed. Instead, a nucleus from the fertilizing cell and a nucleus from the ascogonium become associated and begin to divide synchronously. The products of these nuclear divisions (still in pairs of unlike mating type, i.e. A/a) migrate into numerous ascogenous hyphae, which then begin to grow out of the ascogonium. Each of these ascogenous hypha bends to form a hook (or crozier) at its tip and the A and a pair of haploid nuclei within the crozier divide synchronously. Next, septa form to divide the crozier into three cells. The central cell in the curve of the hook contains one A and one a nucleus (see Figure). This binuclear cell initiates ascus formation and is called an "ascus-initial" cell. Next the two uninucleate cells on either side of the first ascus-forming cell fuse with each other to form a binucleate cell that can grow to form a further crozier that can then form its own ascus-initial cell. This process can then be repeated multiple times.

After formation of the ascus-initial cell, the A and a nucleus fuse with each other to form a diploid nucleus (see Figure). This nucleus is the only diploid nucleus in the entire life cycle of N. crassa. The diploid nucleus has 14 chromosomes formed from the two fused haploid nuclei that had 7 chromosomes each. Formation of the diploid nucleus is immediately followed by meiosis. The two sequential divisions of meiosis lead to four haploid nuclei, two of the A mating type and two of the a mating type. One further mitotic division leads to four A and four a nucleus in each ascus. Meiosis is an essential part of the life cycle of all sexually reproducing organisms, and in its main features, meiosis in N. crassa seems typical of meiosis generally.

As the above events are occurring, the mycelial sheath that had enveloped the ascogonium develops as the wall of the perithecium, becomes impregnated with melanin, and blackens. The mature perithecium has a flask-shaped structure.

A mature perithecium may contain as many as 300 asci, each derived from identical fusion diploid nuclei. Ordinarily, in nature, when the perithecia mature the ascospores are ejected rather violently into the air. These ascospores are heat resistant and, in the lab, require heating at 60 °C for 30 minutes to induce germination. For normal strains, the entire sexual cycle takes 10 to 15 days. In a mature ascus containing eight ascospores, pairs of adjacent spores are identical in genetic constitution, since the last division is mitotic, and since the ascospores are contained in the ascus sac that holds them in a definite order determined by the direction of nuclear segregations during meiosis. Since the four primary products are also arranged in sequence, a first division segregation pattern of genetic markers can be distinguished from a second division segregation pattern.

Fine structure genetic analysis

Because of the above features N. crassa was found to be very useful for the study of genetic events occurring in individual meioses. Mature asci from a perithecium can be separated on a microscope slide and the spores experimentally manipulated. These studies usually involved the separate culture of individual ascospores resulting from a single meiotic event and determining the genotype of each spore. Studies of this type, carried out in several different laboratories, established the phenomenon of "gene conversion" (e.g. see references^[11][12][13]).

As an example of the gene conversion phenomenon, consider genetic crosses of two N. crassa mutant strains defective in gene pan-2. This gene is necessary for the synthesis of pantothenic acid (vitamin B5), and mutants defective in this gene can be experimentally identified by their requirement for pantothenic acid in their growth medium. The two pan-2 mutations B5 and B3 are located at different sites in the pan-2 gene, so that a cross of B5 ´ B3 yields wild-type recombinants at low frequency.^[12] An analysis of 939 asci in which the genotypes of all meiotic products (ascospores) could be determined found 11 asci with an exceptional segregation pattern. These included six asci in which there was one wild-type meiotic product but no expected reciprocal double-mutant (B5B3) product. Furthermore, in three asci the ratio of meiotic products was 1B5:3B3, rather than in the expected 2:2 ratio. This study, as well as numerous additional studies in N. crassa and other fungi (reviewed by Whitehouse^[14]), led to an extensive characterization of gene conversion. It became clear from this work that gene conversion events arise when a molecular recombination event happens to occur near the genetic markers under study (e.g. pan-2 mutations in the above example). Thus studies of gene conversion allowed insight into the details of the molecular mechanism of recombination. Over the decades since the original observations of Mary Mitchell in 1955,^[11] a sequence of molecular models of recombination have been proposed based on both emerging genetic data from gene conversion studies and studies of the reaction capabilities of DNA. Current understanding of the molecular mechanism of recombination is discussed in the Wikipedia articles Gene conversion and Genetic recombination. An understanding of recombination is relevant to several fundamental biologic problems, such the role of recombination and recombinational repair in cancer (see BRCA1) and the adaptive function of meiosis (see Meiosis).

Adaptive function of mating type

That mating in N. crassa can only occur between strains of different mating type suggests that some degree of outcrossing is favored by natural selection. In haploid multicellular fungi, such as N. crassa, meiosis occurring in the brief diploid stage is one of their most complex processes. The haploid multicellular vegetative stage, although physically much larger than the diploid stage, characteristically has a simple modular construction with little differentiation. In N. crassa, recessive mutations affecting the diploid stage of the life cycle are quite frequent in natural populations.^[15] These mutations, when homozygous in the diploid stage, often cause spores to have maturation defects or to produce barren fruiting bodies with few ascospores (sexual spores). The majority of these homozygous mutations cause abnormal meiosis (e.g. disturbed chromosome pairing or disturbed pachytene or diplotene).^[16] The number of genes affecting the diploid stage was estimated to be at least 435^[15] (about 4% of the total number of 9,730 genes). Thus, outcrossing, promoted by the necessity for union of opposite mating types, likely provides the benefit of masking recessive mutations that would otherwise be deleterious to sexual spore formation (see Complementation (genetics)).

Current research

Neurospora crassa is not only a model organism for the study of phenotypic types in knock-out variants, but a particularly useful organism widely used in computational biology and the circadian clock. It has a natural reproductive cycle of 22 hours and is influenced by external factors such as light and temperature. Knock out variants of wild type N. crassa are widely studied to determine the influence of particular genes (see Frequency (gene)).

See also

• Charles Yanofsky – American geneticist (1925–2018)
• David Perkins – American geneticist
• Edward Tatum – American geneticist
• Fluffy transcription factor – Gene of Neurospora crassa required for asexual sporulation
• George Beadle – American geneticist
• Norman Horowitz – American geneticist
• One gene–one enzyme hypothesis – Theory in genetics
• Robert Metzenberg – American geneticist

Notes and references

References

Neurospora crassa es una especie de hongo moho de la división Ascomycota que suele estar presente en panes. El nombre de su género, significa "espora nerviosa" en griego, ya que se refiere a las estrías características de sus esporas. La primera vez que se detectó a este hongo fue en 1843 cuando infectó a panes de una panadería francesa.^[1]​

En investigación científica, Neurospora crassa se usa como organismo modelo porque es fácil de cultivar y tiene un ciclo de vida haploide que simplifica el análisis genético ya que sus genes recesivos aparecen en la descendencia. El análisis de la recombinación genética se ve facilitado por la disposición ordenada de los productos de meiosis en las ascosporas de Neurospora crassa. Se ha secuenciado todo su genoma en siete cromosomas.^[2]​

Neurospora crassa fue utilizado por Edward Tatum y George Wells Beadle en sus experimentos donde ganaron el Premio Nobel de Medicina y Fisiología de 1958. Beadle y Tatum expuesieron a Neurospora crassa a rayos X, causando mutaciones. Luego observaron fallas en las vías metabólicas causadas por errores en enzimas específicas. Esto los llevó a proponer la hipótesis de "un gen, una enzima" de que genes específicos codifican proteínas específicas. Posteriormente, Norman Horowitz elaboró su hipótesis sobre las rutas enzimáticas, trabajando también con Neurospora crassa.^[3]​

En un artículo del 24 de abril de 2003 publicado por Nature, se informó que el genoma de Neurospora crassa estaba completamente secuenciado. El genoma tiene aproximadamente 43 megabases de largo e incluye aproximadamente 10,000 genes. Hay un proyecto en marcha para producir cepas que contienen mutantes en cada gen de Neurospora crassa. ^[4]​^[5]​

En su entorno natural, Neurospora crassa vive principalmente en regiones tropicales y subtropicales. También se puede encontrar creciendo en materia vegetal muerta después de incendios.^[6]​

Neurospora crassa se utiliza activamente en investigaciones celulares del mundo. Es importante en la elucidación de los eventos moleculares implicados en ritmos circadianos, epigenética y silenciamiento de los genes, la polaridad celular, la fusión celular, el desarrollo, así como muchos aspectos de la biología celular y bioquímica.^[7]​

Referencias

Neurospora crassa est une espèce de champignons filamenteux de la division des Ascomycota. Sa première observation documentée est basée sur une infestation de boulangeries françaises en 1843^[1].

Dans son environnement naturel, N. crassa vit surtout en région tropicale et subtropicale^[2]. On en trouve par exemple sur de la matière végétale morte après un incendie.

Étymologie

Le nom du genre, qui signifie "spore nerveuse" en grec, se réfère aux rayures caractéristiques des spores qui ressemblent à des axones.

Organisme modèle

N. crassa est un organisme modèle très utilisé en science pour plusieurs raisons :

• Il pousse facilement et rapidement.
• Son cycle de vie haploïde simplifie l'analyse génétique, car les traits récessifs se manifesteront dans la descendance.
• Son génome de 7 chromosomes a été entièrement séquencé en 2003^[3].

Neurospora a notamment permis :

• à Edward Tatum et George Wells Beadle, lors d'expériences qui leur valurent le Prix Nobel de physiologie ou médecine, d'exposer des N. crassa à des rayons X, ce qui provoque des mutations puis des déficiences des voies métaboliques dues à des erreurs sur des enzymes spécifiques. Cela entraîna l'hypothèse « un gène, une enzyme », qui stipule que des gènes spécifiques encodent des protéines spécifiques. Cette hypothèse a été solidifiée par le travail de Norman Horowitz travaillant aussi sur la Neurospora.
• de démontrer pour la première fois chez un champignon l'existence d'une horloge biologique circadienne et endogène^{[4],[5],[6],[7]} et de plusieurs oscillateurs responsables de ce rythme circadien^[8],[9].
  De plus, quand sa seule source d'azote est le nitrate, une enzyme (nitrate réductase) se comporte quand elle est active comme un oscillateur endogène (en situation continue d'obscurité ou de lumière). C'est une boucle de rétroaction négative qui entretient ce rythme, avec l'implication probable de glutamine qui inhiberait l'activité du gène de la nitrate réductase ; c'est le premier exemple d'un rythme endogène nycthéméral nutritionnellement induit^[10].
• d'étudier de nombreux aspects de la biologie cellulaire et la biochimie et en particulier d'élucider des événements moléculaires impliqués dans l'épigénétique, la désactivation de certains gènes, la polarité cellulaire, la fusion cellulaire, le développement...
  Cultivé en boite de Petri dans une obscurité constante, ce champignon forme autour du point d'inoculation de très nettes vagues successives et régulières de conidiation (formation de spores asexuées), sur un rythme (quasi-circadien) de 22 h. Au contraire, en pleine lumière, la conidiation est constante. Une souche mutante montre l'importance du gène VVD (codant le photorécepteur impliqués dans la photo-adaptation) ^[11],[12].

Génomique

Dans son édition du 24 avril 2003, la revue Nature annonçait que le génome de N. crassa était complètement séquencé.
Le génome a une longueur d'environ 43 mégabases et comporte environ 10 000 gènes.

Recherche actuelle

Outre être un organisme modèle exploité dans l'étude de caractéristiques phénotypiques, la Neurospora crassa est aussi un organisme particulièrement utile et largement utilisé en bio-informatique et en lien avec l'horloge circadienne. Son cycle reproductif naturel dure 22 heures et peut être affecté par des facteurs externes comme la luminosité^[13].

Notes et références

Voir aussi

Neurospora crassa adalah sejenis kapang roti merah yang termasuk dalam filum Ascomycota. Nama genus, yang berarti "spora saraf" dalam bahasa Yunani, mengacu pada karakteristik striasi pada spora. Laporan pertama yang dipublikasikan tentang jamur ini berasal dari serangan kapang di toko roti di Prancis pada tahun 1843.^[1]

N. crassa digunakan sebagai organisme model karena mudah tumbuh dan memiliki siklus hidup haploid yang membuat analisis genetik sederhana karena sifat resesif akan muncul pada keturunannya. Analisis rekombinasi genetik difasilitasi oleh pengaturan tertata dari hasil meiosis di askospora Neurospora. Seluruh genomnya yang terdiri dari tujuh kromosom telah diurutkan.^[2]

Neurospora digunakan oleh Edward Tatum dan George Wells Beadle dalam eksperimen mereka yang memenangkan Penghargaan Nobel Fisiologi atau Kedokteran pada tahun 1958. Beadle dan Tatum memaparkan N. crassa ke sinar-X, menyebabkan mutasi. Mereka kemudian mengamati kegagalan pada jalur metabolisme yang disebabkan oleh kesalahan pada enzim tertentu. Hal ini menyebabkan mereka mengajukan hipotesis "satu gen, satu enzim" bahwa gen tertentu mengkode untuk protein tertentu. Hipotesis mereka kemudian dikembangkan nenjadi jalur enzim oleh Norman Horowitz, juga menggunakan Neurospora. Seperti yang dikenang Norman Horowitz pada tahun 2004^[3] "Eksperimen ini mendirikan ilmu tentang apa yang oleh Beadle dan Tatum disebut 'genetika biokimia'. Sebenarnya, mereka terbukti menjadi senjata pembuka dalam hal yang kemudian menjadi genetika molekuler dan semua perkembangan yang mengikutinya."

Dalam edisi 24 April 2003 Nature, genom N. crassa dilaporkan telah sepenuhnya diurutkan.^[4] Genom ini panjangnya sekitar 43 megabasa dan mencakup sekitar 10.000 gen. Ada sebuah proyek yang sedang berjalan untuk menghasilkan strain yang mengandung mutan knockout setiap gen N. crassa.^[5]

Di lingkungan alaminya, N. crassa tinggal terutama di daerah tropis dan subtropis.^[6] N. crassa dapat ditemukan tumbuh pada materi tanaman mati setelah kebakaran.

Neurospora secara aktif digunakan dalam penelitian di seluruh dunia. N. crassa penting dalam penjelasan peristiwa molekuler yang terlibat dalam ritme sirkadian, epigenetika dan peredaman gen, polaritas sel, fusi sel, perkembangan, serta banyak aspek biologi sel dan biokimia.

Strain dan bahan lainnya untuk bekerja dengan Neurospora tersedia di Fungal Genetics Stock Center.

Catatan

Referensi

Pranala luar

• Neurospora crassa genome [1]
• "The Neurospora Homepage". Fungal Genetics Stock Center (FGSC). Diakses tanggal December 27, 2005.
• "The Neurospora Compendium". Fungal Genetics Stock Center (FGSC). Diakses tanggal December 27, 2005.
• "The Neurospora-Fungal Genome Initiative". Neurospora Genome Project. Diakses tanggal June 12, 2015.
• "Trans-NIH Neurospora Initiative". National Institutes of Health (NIH — United States). Diakses tanggal December 27, 2005.
• [2] Montenegro-Montero A. (2010) "The Almighty Fungi: The Revolutionary Neurospora crassa". A historical view of the many contributions of this organism to molecular biology.

Templat:Model Organisms

La Neurospora crassa è una specie di muffa del pane appartenente alla famiglia Sordariaceae (phylum Ascomycota).^[1] In natura la si trova soprattutto in regioni tropicali e subtropicali.

Il ciclo vitale

N. crassa è un importante organismo modello in campo scientifico, perché è facile da crescere e si sviluppa con un ciclo vitale aplonte, che quindi per la maggior parte è aploide, il che rende facile l'analisi genetica: un allele recessivo sarà facilmente individuabile perché non viene "coperto" dall'allele dominante. Il ciclo vitale completo prevede la produzione di spore chiamate conidi, le quali danno origine ad un micelio, dal quale si svilupperanno altri conidi. Questa fase del ciclo vitale è a riproduzione asessuale e procede tramite divisioni mitotiche. Esistono due tipi di conidi:

• macroconidi: contengono da 4 a 8 nuclei e sono in maggioranza;
• microconidi: contengono un solo nucleo e sono molto meno frequenti.

In condizioni di stress (ad esempio su terreni impoveriti) mating types diversi di N. crassa possono incrociarsi, analogamente a quanto avviene per lieviti mat a e mat α, anche se con un meccanismo diverso. L'incrocio di mating types diversi porta alla formazione di corpi fruttiferi, i quali producono aschi contenenti ascospore. Questo tipo di riproduzione è una riproduzione sessuale, in quanto fondata sulla meiosi. Le ascospore sono ovviamente aploidi. Esse hanno la capacità di riprendere

Il genoma

L'intero genoma di N. crassa è stato sequenziato e pubblicato sul numero di Nature del 24 aprile 2003. Il genoma consta di circa 43 Mb e circa 10 000 geni. È attualmente in corso un progetto che mira alla produzione di mutanti knock-out per ogni gene di N. crassa.

Note

Schematisch voorbeeld van een ascogonium en antheridium met trichogyne

Neurospora crassa is een rode broodschimmel, die behoort tot de ascomyceten. De eerste gepubliceerde vermelding betrof aantastingen in Franse bakkerijen in 1843.^[1]

Het is in de biologie een bekend modelorganisme, die gemakkelijk op een kunstmatig groeimedium te kweken is. Door de haploïde levenscyclus is een genetische analyse eenvoudig uit te voeren, omdat de expressie van recessieve genen direct zichtbaar is bij de nakomelingen. De analyse van de recombinatie is gemakkelijker door de volgorde van de meiose producten in de ascospore. De ascosporen liggen namelijk op één rij.

Neurospora crassa werd door Edward Tatum en George Wells Beadle als onderzoeksmodel gekozen. Voor hun werk verkregen ze in 1958 de Nobelprijs voor de Fysiologie of Geneeskunde. Voor het opwekken van mutaties werd de schimmel bestraald met ionisierende stralen. Aansluitend werd de stofwisseling onderzocht op defecte enzymatische activiteit. Uit de onderzoeksresultaten werd door hen de één gen op één enzym hypothese opgesteld, één gen codeert voor één enzym. Deze hypothese blijkt tegenwoordig nog maar beperkt te gelden (zie:Desoxyribonucleïnezuur#Functies). Hun hypothese werd later door Norman Horowitz gebruikt bij zijn onderzoek naar metabole reactiepaden van enzymen. Ook hij gebruikte Neurospora crassa bij zijn onderzoek, waarnaar hij verwees bij zijn publicatie in 2004^[2] Deze experimenten vormden het fundament voor wat Beadle en Tatum de ‘biochemische genetica’ noemden.

In april 2003 werd in Nature het gesequenste genoom van N. crassa gepubliceerd. Het is ongeveer 43 megabasen groot en bevat afgerond 10.000 genen.^[3]

Neurospora crassa komt van nature vooral voor in de tropische en subtropische gebieden en overwegend op dood plantenmateriaal. Op hostie kleurt de schimmel deze rood wat de verkeerde indruk van een bloedwonder geeft.^[4]

Stammen en ander materiaal van Neurospora crassa zijn te verkrijgen bij het Fungal Genetics Stock Center^[5]

Levenscyclus

De perithecia worden alleen gevormd als twee mycelia met een verschillend paringstype met elkaar in contact komen. Er zijn twee paringstypen: type A en type a. Morfologisch zijn deze twee typen niet van elkaar te onderscheiden. Protoperithecia worden in het laboratorium gemakkelijk gevormd op een vast agarmedium met een relatief laag stikstofgehalte.^[6] Gebrek aan stikstof is noodzakelijk voor de genexpressie van genen die betrokken zijn bij de seksuele ontwikkeling^[7] Bij compatibiliteit vormen zich op de schimmeldraden gametangiën, de bouwcellen voor de gameten, waarin zich talrijke celkernen verzamelen. Uit een zeer fijne, vertakte, gespiraliseerde, meercellige schimmeldraad, de trichogyne, die uit een van de gametangiën, nu ascogonium genoemd, ontstaat, vormt zich een verbinding waardoor de celkernen uit het andere gametangium, nu antheridium genoemd, zich naar het ascogonium kunnen bewegen.

De opeenvolgende stappen in het fusieproces van A en a haploide cellen zijn beschreven door Fincham and Day^[8] en Wagner en Mitchell.^[9] Na de fusie van de cellen volgt niet direct de fusie van de kernen. Eerst gaan de bij elkaar horende kernen van de bevruchtende cel (het antheridium) en die van het ascogonium zich synchroon delen. Vervolgens kromt de top en vormt zo aan de top een haak in de vorm van een bisschopsstaf. Daarna worden er twee tussenwanden gevormd. De middelste cel bevat één kern type A en één kern type a. Deze tweekernige cel start de vorming van een ascus en wordt de “initiële ascuscel” genoemd. De twee overgebleven eenkernige cellen smelten vervolgens samen. Deze tweekernige cel kan op zich ook weer haakvormig worden en een eigen initiële ascuscel vormen. Dit proces kan zich vele malen herhalen.

Na de vorming van de initiële ascuscel smelten de twee kernen samen en vormen een diploïde cel. Dit is het enige diploïde stadium van de schimmel. De diploïde kern bevat 14 chromosomen. Direct na de vorming van de diploïde kern gaat deze zich delen door een eerste meiotische deling en worden er na een tweede meiotische deling vier haploïde kernen gevormd, twee van het type A en twee van het type a. Na vervolgens een mitotische deling zijn er in elke ascus vier kernen van het type A en vier kernen van het type a.

Het mycelium dat het ascogonium omgeeft vormt tijdens bovengenoemd proces de wand van het perithecium, wordt geïmpregneerd met melanine en kleurt zwart. Het rijpe perithecium heeft een flesvormige structuur.

In een volgroeid perithecium kunnen wel 300 asci voorkomen, afkomstig van gefuseerde diploïde kernen. In de natuur worden de rijpe ascosporen met kracht de lucht in geschoten. Deze ascosporen zijn hitte resistent en in het laboratorium moeten ze voor de kieming gedurende 30 minuten verhit worden bij 60 °C. Voor gewone stammen duurt de volledige seksuele cyclus 10 tot 15 dagen. In een rijpe ascus met acht ascosporen hebben de naast elkaar liggende sporen dezelfde genetische samenstelling, omdat de laatste deling een mitotische is en de ascosporenzak de sporen op hun plaats houdt. De volgorde van de sporen in de sporenzak is bepaald door de kerndelingen tijdens de meiose. Omdat de vier primaire producten ook op volgorde liggen kan het eerste splitsingspatroon (meiose) van genetische merkers onderscheiden worden van het tweede splitsingspatroon (mitose).

Systematiek

N. crassa dient als vertegenwoordiger van de clade van het taxon Nucletmycea.^[10]

Externe links

• (en) Foto's
• (en) Systematic Study of Chaetosphaeria and Lasiosphaeria geraadpleegd op 2013-03-27
• (de) Schimmel met Jetlag^{[dode link]}

Zie de categorie Neurospora crassa van Wikimedia Commons voor mediabestanden over dit onderwerp.

Neurospora crassa – gatunek grzybów z rzędu Sordariales^[1]. Typ czerwonej pleśni z gromady workowców (Ascomycota), tworzącej się głównie na chlebie, występujący również w terenach podmokłych i tropikalnych. Grecka nazwa oznacza "grzyb nerwowy", odnosi się do charakterystycznego prążkowania strzępek. Pierwsze opublikowane doniesienia o tym gatunku, pochodzą z zarażenia w jednej z francuskich piekarni w 1843 roku^[2].

Systematyka i nazewnictwo

Pozycja w klasyfikacji według Index Fungorum: Neurospora, Sordariaceae, Sordariales, Sordariomycetidae, Sordariomycetes, Pezizomycotina, Ascomycota, Fungi^[1].

Znaczenie

N. crassa jest wykorzystywana w biologii jako organizm modelowy. Edward Lawrie Tatum i George Wells Beadle wykorzystali promieniowanie rentgenowskie do mutagenezy N. crassa i wykazali, że uzyskane w ten sposób mutacje powodowały zmiany w funkcjonowaniu enzymów zaangażowanych w metabolizm. Na podstawie tych badań sformułowali hipotezę "jeden gen = jeden enzym". W 1958 r. za swoje badania otrzymali Nagrodę Nobla w dziedzinie fizjologii i medycyny.

W 2003 poznano cały genom tego organizmu, który ma ok. 43 miliony par zasad i zawiera ok. 10000 genów na 7 chromosomach^[3]. Realizowany jest projekt badający efekty uszkodzenia po kolei każdego genu tego organizmu^[4].

Przypisy

Neurospora crassa é uma espécie de fungo pertencente ao filo Ascomycota.

É uma espécie importante devido ao seu uso intensivo em ciência: é portanto classificado como um organismo modelo.

Este uso intensivo advém das suas características:

• Fácil manuseio e reprodução;
• Ciclo de vida haplóide.

Por ser haplóide, as análises genéticas estão facilitadas porque a descendência irá revelar os traços recessivos.

Em 24 de Abril de 2003, a revista Nature anunciou o sequenciamento completo do genoma desta espécie. O seu genoma tem aproximadamente 43 milhões de bases, compreendendo cerca de 10 000 genes.

Referências

• Osherov, N & May, GS (2001), "The molecular mechanisms of conidial germination", FEMS Microbiol Lett, vol. 199(2):153-60. PMID 11377860 (em inglês)
• Froehlich, AC, Noh, B & Vierstra, RD, Loros J & Dunlap JC (2005), "Genetic and molecular analysis of Phytochromes from the filamentous fungus Neurospora crassa", Eukaryot Cell, vol. 4(12):2140-52. PMID 16339731 (em inglês)
• Horowitz, NH (1991), "Fifty years ago: the Neurospora revolution", Genetics. PMID 1827628 (em inglês)
• Horowitz, NH, Berg, P & Singer, M, Lederberg J, Susman M, Doebley J & Crow JF. (2004), "A centennial: George W. Beadle, 1903-1989", Genetics, vol. 166(1):1-10. PMID 15020400 (em inglês)
• Kaldi, K, Gonzalez, BH & Brunner, M (2005), "Transcriptional regulation of the Neurospora circadian clock gene wc-1 affects the phase of circadian output", EMBO Rep. PMID 16374510 (em inglês)
• Pittalwala, Iqbal (2003), "UC Riverside scientists contribute to study that unveils genome sequence of bread mold", Newsroom (University of California, Riverside) (em inglês)
• Ruoff, P, Loros, JJ & Dunlap, JC (2005), "The relationship between FRQ-protein stability and temperature compensation in the Neurospora circadian clock", Proc Natl Acad Sci USA. PMID 16314576 (em inglês)

Neurospora crassa je grzib^[1], co go ôpisoł Shear & B.O. Dodge 1927. Neurospora crassa nŏleży do zorty Neurospora i familije Sordariaceae.^[2][3] Żŏdne podgatōnki niy sōm wymianowane we Catalogue of Life.^[2]

Przipisy

Galeryjŏ fotografiji

Neurospora crassa, asklı mantarlara ait bir kırmızı ekmek mantarı türüdür. "Sinir sporu" anlamına gelen Neurospora ismi sporların üzerindeki çizgilerin aksonlara benzemesinden dolayıdır.

Tarih

N. crassa, laboratuvarda kolay büyütülebildiği ve haploit hayat döngüsü genetik analizi kolay kıldığı için bilimde bir model organizma olarak ün yapmıştır. Neurospora genetiği üzerinde araştırma yapan Edwart Tatum ve George Wells Beadle Nobel Fizyoloji veya Tıp Ödülü'nü kazanmıştır. Beadle ve Tatum, N. crassa'yı X ışınlarına maruz bırakıp mutasyonlara yol açmış, sonra da belli enzimlerde bozukluklardan kaynaklanan metabolik bozukluklar gözlemlemişlerdir. Bu deneyler, iki araştırmacıyı belli genlerin belli proteinleri kodladığı sonucuna ulaştırmış, "bir gen, bir enzim" hipotezine ortaya çıkarmıştır. Enzimlerin birden fazla proteinden oluştuğu fark edilince bu deyim "bir gen, bir polipeptit" olarak değiştirilmiştir.

Neurospora'da yapılan araştırmalar genetik ve epigenetik susturmanın örneklerini göstermiş, ritmik sporülasyonun çalışılması sonucunda güncel ritim mekanızmasının anlaşılmasında önemli ilerlemeler kaydedilmiştir.

N. crassa'nın genomunun dizini 2003'te çözülmüştür. Yedi kromozomdan oluşan genom toplam 43 megabaz uzunluğunda olup yaklaşık 10.000 genden oluşmaktadır. Bu organizmadaki her bir gende ayrı birer mutasyon oluşturulmasını amaçlayan proje sürmektedir.

Doğal ortamında N. crassa tropik ve subtropikal bölgelerde yaşar. Orman yangınlarından sonra bitkilerin üzerinde büyüdüğü sıkça görülür.

Model organizma olarak avantajları

• Genetik analiz yapmak kolaydır. Askosporların izole edilmesi yoluyla haploid hücreler kolayca elde edilebilir, tetrad analizi ile mayoz bölünmenin dört ürünü ayırdedilebilir. Ask ince uzun olduğu için Metafaz I'de birbirinden ayrılan hücreler yan yana dururlar. Bu özellik genlerin haritalanmasını yarar.
• Konidyum adlı keselerde cinsiyetsiz sporlar üretilir. Bu sporlar ilginç Neurospora genotiplerinin izole edilmesini sağlar.
• Genetik ve fizik kromozom haritaları mevcuttur.
• Beslenme gereksinimleri basittir, büyüme hızı yüksek, kültürleme ucuz, jenerasyon süresi 3 haftadan kısadır.
• Hayat döngüsünün vejetatif ve eşeysel evrelerinde farklı hücre tıpleri mevcuttur. Yaşamının çoğu haploit olduğu için gen ifadesini çalışmak kolaydır, baskın ve çekinik genler sorun yaratmaz.
• Çeşitli moleküler ve genetik teknikler mevcuttur, örneğin ayarlanabilir promotörler, belli genomik konumlara DNA sokma yöntemleri, ve gerekli gen mutasyonlarının ölümcül olmamasını sağlama yöntemleri gibi.
• Bilimsel camiaya açık, on binden fazla suştan oluşan bir kültür koleksiyonu gen mutasyonları, kromozom düzenlenmeleri ve doğal populasyonlardan izolatlar içermektedir.
• Genetik transformasyon çok verimli olarak yapılabilir. Yeni genlerin nakavt mutasyonları genom projesi dahilinde sipariş edilebilir.
• Pek çok millete yayılmış bir araştırma komünitesi bilimsel kaynaklarını ve sonuçlarını paylaşmaktadır.

Kaynakça

• Trans-NIH Neurospora Initiative (İngilizce)

Dış bağlantılar

• The Neurospora Homepage
• The Neurospora Compendium
• Neurospora crassa Release 7
• Neurospora Genome Project
• Neurospora Initiative
• Neurospora'nın hayat döngüsü
• TAXONOMIC CLASSIFICATION: AN OVERVIEW
• videolar

• 1 Биологические особенности
• 2 Использование в генетических исследованиях
• 3 Другие виды нейроспоры
• 4 Литература
• 5 Ссылки

粉色麵包黴菌（Neurospora crassa，又譯紅麵包黴菌等）是一種屬於子囊菌門（Ascomycota）的黴菌。由於生長容易，且擁有單倍體世代，使隱性遺傳可直接展現，進而使遺傳學分析較為簡易，因此是一種生物學上的模式生物。本屬名字意為“神經孢子”，指的是孢子 中的特徵條紋。這種真菌的第一次發布是於1843年從法國麵包店的侵染。^[1]

N. crassa的早期研究者喬治·比德爾（George Wells Beadle）與愛德華·塔特姆（Edward Tatum），在實驗中利用X射線照射使N. crassa發生突變，進而觀察到因酵素失效而遭破壞的生化代謝途徑，並由此確立了基因編碼與蛋白質的關係。兩人因此獲得1958年諾貝爾生理學或醫學獎。

N. crassa擁有的全部7條染色體，完整的基因組已經大致定序完成^[2]。並於2003年4月24日發表於《自然》期刊^[3]。其基因組大小約43Mb，含有約1萬個基因。目前正在進行每一個N. crassa基因的基因敲除（knockout）測試。^[4]

在自然環境中，N. crassa主要生活在熱帶和亞熱帶地區^[5]。它被發現可以在火災後死去的植物物質裡生長。

N. crassa被積極應用於世界各地的研究。它是在參與晝夜節律，表觀遺傳學和基因沉默（英语：Gene silencing），細胞極性（英语：Cell polarity），細胞融合，發育，以及細胞生物學和生物化學的許多方面闡明重要的分子事件。

菌株和N. crassa工作的其他材料都可以從真菌遺傳學現貨中心(Fungal Genetics Stock Center)獲得。

參看

• 乔治·韦尔斯·比德尔（George Wells Beadle)
• 爱德华·劳里·塔特姆 (Edward Lawrie Tatum)

參考文獻

アカパンカビ（学名: Neurospora crassa）は、子嚢菌門に属する糸状菌の一種。モデル生物としても重要である。

特徴[編集]

アカパンカビは小さな球状の子実体を作る子のう菌の1種で、古典的には子嚢菌門核菌綱タマカビ目（Sphaeriales）に分類してきた。分子系統解析に基づく現在の分類では、子嚢菌門フンタマカビ綱フンタマカビ目フンタマカビ科となる。

アカパンカビ（red bread mould）の名は、分生子が赤みを帯びていることに由来する。したがって、和名そのものはこの菌のアナモルフ(不完全世代)に与えられたものである。

通常の分生子は分節型で、この形のものは不完全菌としてはMonilia属に含まれる。気中に伸び、枝分かれした菌糸が、寸断されるようにして、個々には楕円形の分生子の鎖になる。寒天培地上では非常に生育が早く、径10cmのシャーレが一日でいっぱいになる。菌糸は主として寒天表面か気中に伸びて、ふわふわとした姿で、すみやかに分生子を形成するので、全体に赤みを帯びる。

自家不和合性で、性的に和合性を有する菌株同士が摂食したときにのみ有性生殖が行われ、子実体が形成される。

子実体はほぼ球形・黒色で、頂端がやや突出した壷状をなし、その先端に内部への入り口が開く。内部には細長い子嚢が束になって形成され、子嚢内には子嚢胞子が八個入っている。

フンタマカビ科の近縁種に、同じ生活環および形状はほぼ同様であるが分生子が黄色を呈するキパンカビ(キイロパンカビ)がある^[要出典]。

利用[編集]

古くから遺伝学の研究に用いられている。これは以下の特徴によるものである。

• 人工培養が簡単であること。
• 栄養要求がごく単純であり、その分析が容易であること。
• 子嚢が細長く、その内部の胞子が一列に並ぶことは、減数分裂の結果として形成された遺伝子型の異なる胞子を、遺伝子型を特定しつつ選択的に取り出すのに好都合であること。
• 分生子にX線を照射して突然変異を誘発するのが簡単である。

特に突然変異で生じた栄養要求株の研究は一遺伝子一酵素説の基礎となり、遺伝子の機能やその実体の解明への糸口となった事は有名である。また、最初にゲノム配列が解読された糸状菌でもある。

他方、分生子が簡単に空中に飛散し、分生子形成や成長も早い性質は、微生物培養においてはやっかいなものである。望まない場合にこの菌が侵入すると、たちまちのうちにあちこちの培地に侵入し、しかもすぐに広がって分生子をまき散らすので、もっとも恐るべき雑菌の一つである。

その他[編集]

ヨーロッパではごく普通に出現するカビである。非常に成長が早く、分生子形成も素速く行なうため、一夜にしてパンが全体に薄赤く染まる、といった現象を引き起こす。また、子のう胞子が熱を受けると発芽しやすくなる性質があるので、たき火のあとなどに発生することも多く、パン工場なども発生が多い。日本では出現頻度は高くないが高湿な時期にキパンカビが発生した例がある。アカパンカビ、キパンカビともに前述のとおり焚き火の燃えさしや焦げた穀類の種皮などから発生するので、元来山火事跡や野火跡のような環境に適応して派生した子嚢菌ではないかという説もある。

붉은빵곰팡이는 빵곰팡이속에 속하며 학명은 Neurospora crassa이다. 옥수수 속이나 빵 표면에 다핵의 다세포 균사체가 성장하여, 분생 포자 자루 위에 분홍색의 큰 달걀형 분생 포자가 생겨 무성적으로 번식하게 된다. 한편, 유성 생식에서는 장낭기에서 수정모가 자라고 이것과 분생 포자가 접합하여 장낭사가 만들어져 어두운 빛깔의 자낭과가 된다. 오늘날에는 이러한 붉은빵곰팡이가 유전자와 효소 작용과의 관계 연구에 이용되고 있다.

외부 링크

• Neurospora crassa genome [1]
• “The Neurospora Homepage”. 《Fungal Genetics Stock Center (FGSC)》. 2005년 12월 27일에 확인함.
• “The Neurospora Compendium”. 《Fungal Genetics Stock Center (FGSC)》. 2005년 12월 27일에 확인함.
• “The Neurospora-Fungal Genome Initiative”. 《Neurospora Genome Project》. 2016년 3월 4일에 원본 문서에서 보존된 문서. 2015년 6월 12일에 확인함.
• “Trans-NIH Neurospora Initiative”. 《National Institutes of Health (NIH — United States)》. 2005년 12월 27일에 확인함.
• [2] Montenegro-Montero A. (2010) "The Almighty Fungi: The Revolutionary Neurospora crassa". A historical view of the many contributions of this organism to molecular biology.

이 문서에는 다음커뮤니케이션(현 카카오)에서 GFDL 또는 CC-SA 라이선스로 배포한 글로벌 세계대백과사전의 "붉은빵곰팡이" 항목을 기초로 작성된 글이 포함되어 있습니다.