Reproductive Genetics of neurospora tetrasperma

雅各布森97-13015不同于粗毛核菌，它是异倍体，产生两种不同交配型的单倍体子囊孢子，而四种核型核菌是自育的，因为每个子囊柄接收每个交配型的一个核。这种生殖系统被称为假同源生殖，因为偶尔单一交配型孢子是自交不育和异交的，这表明自然界中存在异交的可能性。在一个水平上，四种拟同源异株的机制似乎非常简单。第二次减数分裂的纺锤体重叠，再加上随后的程序性核运动，导致每个子囊产生四个异核子囊孢子，而不是粗毛拟青霉和其他真正异源物种的八个典型的子囊孢子。尽管这种产生自交可育的子囊孢子的机制看起来很简单，但现在很清楚的是，假同源异体具有重要而复杂的含义。最近的一项研究表明，实验室中与地理上不同的四种奈瑟曼菌株异交会导致高度的性功能障碍。另一项研究表明，与在真正的异源物种中观察到的重组相比，四种核桃的交配型染色体之间的重组受到了抑制；它还表明，四种核型的交配型染色体和常染色体反映了非常不同的进化历史。矛盾的是，交配型染色体上的重组被抑制，再加上四精核菌独特的性发育途径，产生了在交配型染色体上具有高度异质性的野生型菌株，但在常染色体上的序列实际上是完全同源等位的。这两项研究的结果似乎非常相关。例如，性功能障碍的一个方面似乎涉及由某些基因座的异等位基因带来的原生质不相容。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基因可能反映了这种不相容的避免。这项研究将探讨(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意义。这项研究将为今后的遗传学研究开发四种核型生物作为实验有机体。

Jacobson 97-13015 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 chromosome, 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.