Hirata A, Shimoda C
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Yeast. 1994 Feb;10(2):173-83. doi: 10.1002/yea.320100205.
In order to characterize the morphological steps defined by sporulation (spo) genes during the formation of ascospores in the fission yeast Schizosaccharomyces pombe, we performed an electron microscopic study of the ultrastructure of the spindle pole body (SPB) and of the development of the forespore membrane during the second meiotic division (meiosis II) in sporulation-deficient (spo) mutants (spo4, spo5, spo14 and spo18). No difference was found in terms of the function and the structure of the SPB during the first meiotic division (meiosis I) between the four mutants and wild-type cells. However, during meiosis II, the spo4 and spo18 mutants underwent nuclear division but in neither case were the SPBs modified nor were forespore membranes formed. The SPBs of the spo18 mutant diminished in size after meiosis II and eventually disappeared after 18 h in sporulation medium. By contrast, the SPBs of the spo4 mutant remained unchanged even after an 18-h incubation. The outer plaques of SPBs of spo5 and spo14 mutants were sufficiently modified to allow them to initiate development of the forespore membrane, but the membrane had an abnormally expanded lumen and did not enclose the nuclei during meiosis II. The spo5 mutant produced anucleate spore-like bodies while the spo14 mutant formed unorganized structures with irregular peripheries which, presumably, contained spore-wall precursors, instead of anucleate spore-like bodies. We conclude that the modification of the SPB is essential for the formation of ascospores and at least two genes (spo5 and spo14) participate in the development of the forespore membrane. The defective phenotypes define discrete steps in the development of ascospores, which proceeds via steps defined by the mutant spo4, spo18, spo14 and spo5 genes respectively. Our observations provide further substantial evidence that the SPB plays a pivotal role in the normal development of ascospores in yeasts.
为了描述裂殖酵母粟酒裂殖酵母在形成子囊孢子过程中由孢子形成（spo）基因所定义的形态学步骤，我们对孢子形成缺陷（spo）突变体（spo4、spo5、spo14和spo18）在第二次减数分裂（减数分裂II）期间纺锤极体（SPB）的超微结构以及前孢子膜的发育进行了电子显微镜研究。在四个突变体与野生型细胞之间，第一次减数分裂（减数分裂I）期间SPB的功能和结构未发现差异。然而，在减数分裂II期间，spo4和spo18突变体进行了核分裂，但在这两种情况下，SPB均未发生改变，也未形成前孢子膜。spo18突变体的SPB在减数分裂II后尺寸减小，在孢子形成培养基中培养18小时后最终消失。相比之下，spo4突变体的SPB即使在培养18小时后仍保持不变。spo5和spo14突变体的SPB外板发生了充分改变，使其能够启动前孢子膜的发育，但该膜的管腔异常扩张，在减数分裂II期间未包裹细胞核。spo5突变体产生了无核的类孢子体，而spo14突变体形成了外周不规则的无组织结构，推测其含有孢子壁前体，而非无核的类孢子体。我们得出结论，SPB的修饰对于子囊孢子的形成至关重要，并且至少有两个基因（spo5和spo14）参与前孢子膜的发育。缺陷表型定义了子囊孢子发育中的离散步骤，子囊孢子发育分别通过由突变体spo4、spo18、spoI4和spo5基因所定义的步骤进行。我们的观察结果提供了进一步的重要证据，表明SPB在酵母子囊孢子的正常发育中起关键作用。
