A sensitized genetic background reveals evolution near the terminus of the Caenorhabditis germline sex determination pathway.
A sensitized genetic background reveals evolution near the terminus of the Caenorhabditis germline sex determination pathway.
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DOI：
10.1111/j.1525-142x.2009.00340.x
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发表时间：
2009-07
影响因子：
2.9
通讯作者：
Haag ES
中科院分区：
文献类型：
--
作者：
Hill RC;Haag ES
秀丽线虫和布氏线虫都是能自我繁殖的两性线虫，它们是从雄性/雌性祖先独立进化而来的。在线虫中，通过促进男性抑制转录因子TRA-1的蛋白分解，FmM-1、Fm-2和Fm-3决定了男性的命运。Tra-1和fem突变体的表型在胞体中符合这一简单的线性模型，但在胚系中不符合。虽然XX和XO tra-1(Lf)突变体都有功能正常的雄性Soma，但它们既能产生精子，也能产生卵母细胞。此外，所有三个tra-1；fem双重突变体都保留了预期的雄性胞体，但只产生卵母细胞(胚系fem表型)。因此，特征不佳的tra-1活性对于持续的男性精子发生是重要的，并且fem基因影响生殖系的性别命运，而不是它们在调节tra-1中的作用。Briggsae tra-1突变体在表型上与其对应的线虫相同，而fem突变体在生殖系上不同：xx和xo线虫fem突变体是真正的雌性，但在briggsae中它们是自育的两性。为了进一步探索桥藻两性体如何调节生殖系性别，我们分析了CB-tra-1/CB-fem的相互作用。Cb-tra-1在胚系中与Cb-Fem-2完全上位，不同于同源线虫组合。相反，Cb-Fem-3将Cb-tra-1(Lf)胚系表型转变为在男性体细胞性腺中几乎正常的两性。这表明Cb-Fem-3对Cb-tra-1(Lf)是上位的(与线虫中一样)，并且Cb-fem-3下游的独立因子Cb-tra-1是布里格萨XX生精的正常控制目标。CB-FEM-3(Lf)对Cb-tra-1(Lf)的影响不是通过CB-tra-1可能的直接胚系靶点CB-FOG-3表达的变化来介导的。由于Cb-Fem-2和Cb-Fem-3具有相同的单一突变表型，Cb-tra-1提供了一个敏感的背景，揭示了它们如何促进雄性生殖系发育的差异。这些结果代表了另一种方式，即桥隐杆线虫的种系性别决定与外表相似的线虫的性别决定不一致。
Caenorhabditis elegans and C. briggsae are both self-fertile hermaphroditic nematodes that evolved independently from male/female ancestors. In C. elegans, FEM-1, FEM-2, and FEM-3 specify male fates by promoting proteolysis of the male-repressing transcription factor, TRA-1. Phenotypes of tra-1 and fem mutants are consistent with this simple linear model in the soma, but not in the germ line. While both XX and XO tra-1(lf) mutants have functional male somas, they produce both sperm and oocytes. Further, all three tra-1; fem double mutants retain the expected male soma, but make only oocytes (the germline fem phenotype). Thus, a poorly characterized tra-1 activity is important for sustained male spermatogenesis, and the fem genes affect germline sexual fate independently of their role in regulating TRA-1. C. briggsae tra-1 mutants are phenotypically identical to their C. elegans counterparts, while the fem mutants differ in the germline: XX and XO C. elegans fem mutants are true females, but in C. briggsae they are self-fertile hermaphrodites. To further explore how C. briggsae hermaphrodites regulate germline sex, we analyzed Cb-tra-1/Cb-fem interactions. Cb-tra-1 is fully epistatic to Cb-fem-2 in the germ line, unlike the orthologous C. elegans combination. In contrast, Cb-fem-3 shifts the Cb-tra-1(lf) germline phenotype to that of a nearly normal hermaphrodite in the context of a male somatic gonad. This suggests that Cb-fem-3 is epistatic to Cb-tra-1(lf) (as in C. elegans), and that the normal control of C. briggsae XX spermatogenesis targets Cb-tra-1-independent factors downstream of Cb-fem-3. The effect of Cb-fem-3(lf) on Cb-tra-1(lf) is not mediated by change in the expression of Cb-fog-3, a likely direct germline target of Cb-tra-1. As Cb-fem-2 and Cb-fem-3 have identical single mutant phenotypes, Cb-tra-1 provides a sensitized background that reveals differences in how they promote male germline development. These results represent another way in which C. briggsae germline sex determination is incongruent with that of the outwardly similar C. elegans.