The Perkins Lab -- Neurospora Genetics and Biology
Department of Biological Sciences, Stanford University
Normal meiosis and ascospore development in heterothallic species of Neurospora. (N.B. Raju)
Dodge (1927) initiated studies on ascus development, and McClintock (1945) and Singleton (1953) showed that meiosis and chromosome behavior
in Neurospora are very similar to those of higher plants and animals (see Raju 1980, 1992). After fertilization, haploid nuclei from the two
parents proliferate in ascogenous hyphae. These give rise to asci in which two nuclei of opposite mating type fuse to produce a diploid nucleus. The
diploid nucleus immediately undergoes meiosis (two divisions) and a postmeiotic mitosis resulting in eight haploid nuclei, which are then sequestered
into eight ascospores. A second mitosis in the young ascospores makes them binucleate, and four or five additional mitoses occur later as the black
ascospores mature. Each perithecium produces over 200 asci. The alignment of spindles at the three divisions and the linear ordering of ascospores in
the elongated narrow asci make Neurospora ideal for visually demonstrating the cytological basis of crossing over at the four-strand stage in
meiotic prophase. Ascus development and nuclear events are nearly identical in all eight-spored species of Neurospora except N. pannonica
(Raju 2000), where the immature asci are swollen, and the ascospore order in mature asci may not reflect nuclear events in the ascus.
A nearly complete sequence of chromosome behavior in asci and ascospores is illustrated here with two diagrams and 48 photographs:
38 from N. crassa and 10 from N. discreta (Figs. 13, 14, 22-24, 32, 33, 35, 38, 42).
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Fig 1. Schematic ascus diagrams
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Fig 2. Croziers, young ascus
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Fig 3. Croziers, young asci
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Fig 4. Pachytene, hematoxylin stain
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Fig 5. Pachytene, acriflavin stain
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Fig 6. Pachytene, orcein stain
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Fig 7. Pachytene, orcein stain
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Fig 8. McClintock’s drawings |
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Fig 9. Diplotene |
Fig 10. Diplotene, acriflavin stain
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Fig 11. Diakinesis, acriflavin stain
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Fig 12. Diakinesis, orcein stain
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Permission and Copyright
You may use any of these photos for educational purposes (not for profit). We ask that you use a credit line citing the original reference and the photographer. High-resolution versions of these photos are available upon request from N.B. Raju’s photo collection, see Contacts. If previously published photos are to be used in publication, permission will, of course, be required from the publisher (see the captions of enlarged photos).
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