Abstract
Meiosis in the basidiomycete Coprinus cinereus was analyzed by three dimensional reconstructions of nuclei covering the period from leptotene to telophase II. Crosses involving three different strains (JR52, PR2301 and E991) were used.
The analysis of 94 completely reconstructed nuclei arranged in a temporal sequence according to the morphology of the synaptonemal complex, the centromeres and the centrosomes permitted the following observations and conclusions: (1) The haploid chromosome number of Coprinus cinereus is 13. (2) Reciprocal translocations have been identified in strains PR2301 and E991. In the former strain, the translocation is between chromosomes 3 and 5 and in the latter between chromosomes 1 and 9. (3) Interlockings and chromosome breaks are present during zygotene but at a lower frequency than in organisms with longer chromosomes. The translocation quadrivalents are more often than normal bivalents involved in interlockings and have more chromosome breaks. (4) Transformation of a translocation quadrivalent into two heteromorphic bivalents was only observed once in agreement with the contention that the turnover of the synaptonemal complex required for this transformation is prevented in bivalent regions where crossing over has occurred. (5) Correction of interlockings by the «breakage-reunion» mechanism is complete before mid-late pachytene. (6) The presence of two apparently normal bivalents replacing the translocation quadrivalent in at least one, possibly several, cases suggests that a «retranslocation» has taken place, possibly by a mechanism similar to that responsible for the resolution of interlockings. The implications of this possibility are discussed. (7) During early diplotene the synaptonemal complexes are eliminated from the bivalent arms while synaptonemal complex constituents often remain associated with the centromeres and the chiasmata until late diplotene. (8) Homologous centromere regions remain fused at least until early diakinesis. It is the suggested that this association may serve the same function as chiasmata in maintaining the bivalent configuration up to metaphase I and hence improve the chances of a regular disjunction in bivalents without chiasmata. (9). Recombination nodules are readily identified in the central region of the synaptonemal complex from early zygotene to late diplotene. The total number of nodules expected upon completion of synaptonemal complex formation at late zygotene amounts to 37 and is the same as that observed at early pachytene. The total number of nodules is reduced to 26 before midlate pachytene, a reduction similar to that reported in other organisms. (10) An increasing fraction of the nodules becomes larger and surrounded by chromatin during pachytene—diplotene and by late diplotene, all nodules are replaced by small chromatin condensations—chiasmata. (11) The distribution of nodules among and along the bivalents has been analyzed by comparing the observed distributions and those produced by computer simulation of a random positioning of nodules. The analysis reveals a nearly random distribution at late zygotene while during early pachytene and especially pronounced at mid-late pachytene, the distribution of nodules deviates from a random distribution. The comparison furthermore indicates that the placement of recombination nodules on the bivalents of a nucleus is controlled by nodule/bivalent (bivalent arm) interactions while the interaction between nodules appears to be of less importance.
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Abbreviations
- sd:
-
standard deviation
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Holm, P.B., Rasmussen, S.W., Zickler, D. et al. Chromosome pairing, recombination nodules and chiasma formation in the basidiomycete coprinus cinereus. Carlsberg Res. Commun. 46, 305 (1981). https://doi.org/10.1007/BF02906519
DOI: https://doi.org/10.1007/BF02906519