Reproductive Genetics of Neurospora Tetrasperma

Natvig 96-03902与N. crassa为异宗配合，产生两种不同交配型的单倍体子囊孢子;四精子是自花受精的，因为每个子囊孔接受每个交配类型的一个核。 这种生殖系统被称为假同宗配合，因为偶尔的单交配型孢子是自交不育和异宗配合的，这表明自然界中有异交的潜力。 从一个水平上探讨了N.四精子看起来很简单 在第二次减数分裂时纺锤体的重叠，以及随后的程序化核运动，导致每个孢子囊有4个异生子囊孢子，而不是N. crassa和其他真正的异宗配合物种。 尽管这种产生自花受精子囊孢子的机制看似简单，但现在清楚的是，N。四精子具有重要而复杂的意义。 最近的一项研究表明，实验室异交与地理上不同的N。四精子症导致高水平的性功能障碍。 另一个证明了N.四子草交配型染色体相对于真正异宗配合的物种，如N. crassa的交配型染色体和常染色体，并证明了N.四精子反映了非常不同的进化历史。 巧合的是，在交配型染色体上的抑制重组，加上独特的性发育途径的N。tetrasperma产生了野生型菌株，其在交配型染色体组上具有高水平的异等位性，但在常染色体上的序列上具有几乎完全的同源等位性。 这两项研究的结果似乎是密切相关的。 例如，性功能障碍的一个方面似乎涉及由某些位点的异等位性引起的原生质不相容性。 在野生型菌株中观察到的常染色体序列的高水平同源等位性可能反映了避免这种不相容性。 本研究将探讨（1）性功能障碍的遗传基础和（2）交配型染色体上抑制重组的机制和生物学意义。 我们的研究集中在发育和生命周期生物学的几个基本方面，因此它对高等生物的生殖遗传学具有广泛的影响。 本研究将对N.作为未来遗传学研究的实验生物。

Natvig 96-03902 Unlike N. crassa, which is heterothallic and produces haploid ascospores of two separate mating types, N. tetrasperma is self fertile as a consequence of each ascopore receiving one nucleus of each mating type. This reproductive system has been termed pseudohomothallism, because occasional single mating-type spores are self sterile and heterothallic, suggesting the potential for outcrossing in nature. At one level, the mechanism of pseudohomothallism in N. tetrasperma appears quite simple. An overlap of spindles at the second meiotic division, together with subsequent programmed nuclear movements, leads to four heterokaryotic ascospores per ascus, instead of the eight typical of N. crassa and other truly heterothallic species. Despite this deceptively simple mechanism for creating self-fertile ascospores, it is now clear that pseudohomothallism in N. tetrasperma has important and complex implications. One recent study revealed that laboratory outcrossing with geographically diverse strains of N. tetrasperma results in high levels of sexual dysfunction. Another demonstrated that recombination between N. tetrasperma mating-type chromosomes is suppressed relative to that observed for truly heterothallic species, such as N. crassa; and it demonstrated that the mating-type chromosomes and autosomes of N. tetrasperma reflect very different evolutionary histories. Paradoxically, suppressed recombination on the mating-type chromosome, coupled with the unique sexual developmental pathway of N. tetrasperma, has produced wild-type strains with high levels of heteroallelism on the mating-type chromoqome, but with virtually complete homoallelism for sequences on autosomes. The results of these two studies appear to be very much interrelated. For example, one aspect of sexual dysfunction seems to involve protoplasmic incompatibility brought about by heteroallelism at certain loci. The high levels of homoallelism observed for autosomal sequences in wild type strains may reflect an avoidance of this incompatibility. This research will investigate (1) the genetic bases of sexual dysfunction and (2) the mechanism and biological significance of suppressed recombination on the mating-type chromosome. Our study focuses on several fundamental aspects of developmental and life-cycle biology, and it therefore has broad implications for reproductive genetics in higher organisms. This study will go far toward developing N. tetrasperma as an experimental organism for future genetic studies.