Abstract Sexual characteristics and reproductive systems are dynamic traits in many taxa, but the developmental modifications that allow change and innovation are largely unknown. A leading model for this process is the evolution of self-fertile hermaphrodites from male/female ancestors. However, these studies require direct analysis of sex-determination in male/female species, as well as in the hermaphroditic species that are related to them. In Caenorhabditis nematodes this has only become possible recently, with the discovery of new species. Here, we use gene editing to characterize major sex-determination genes in C. nigoni, a sister to the widely studied hermaphroditic species C. briggsae. These two species are close enough to mate and form partially fertile hybrids. First, we find that tra-1 functions as the master regulator of sex in C. nigoni, in both the soma and the germ line. Surprisingly, these mutants make only sperm, in contrast to tra-1 mutants in related hermaphroditic species. Moreover, the XX mutants display a unique defect in somatic gonad development that is not seen elsewhere in the genus. Second, the fem-3 gene acts upstream of tra-1 in C. nigoni, and the mutants are females, unlike in the sister species C. briggsae, where they develop as hermaphrodites. This result points to a divergence in the role of fem-3 in the germ line of these species. Third, tra-2 encodes a transmembrane receptor that acts upstream of fem-3 in C. nigoni. Outside of the germ line, tra-2 mutations in all species cause a similar pattern of partial masculinization. However, heterozygosity for tra-2 does not alter germ cell fates in C. nigoni, as it can in sensitized backgrounds of two hermaphroditic species of Caenorhabditis. Finally, the epistatic relationships point to a simple, linear germline pathway in which tra-2 regulates fem-3 which regulates tra-1, unlike the more complex relationships seen in hermaphrodite germ cell development. Taking these results together, the regulation of sex determination is more robust and streamlined in the male/female species C. nigoni than in related species that make self-fertile hermaphrodites, a conclusion supported by studies of interspecies hybrids using sex-determination mutations. Thus, we infer that the origin of self-fertility not only required mutations that activated the spermatogenesis program in XX germ lines, but prior to these there must have been mutations that decanalized the sex-determination process, allowing for subsequent changes to germ cell fates.

Jonathan P Harbin

Yongquan Shen

Shin-Yi Lin

Kevin Kemper

Eric S Haag

Erich M Schwarz

Ronald E Ellis

Genetics

GENETICS 由美国遗传学会出版，这是一个学术团体，旨在通过促进我们对遗传学的理解来加深我们对生活世界的理解。自 1916 年以来，GENETICS 发表了高质量的原创研究，展示了与遗传学和基因组学有关的新发现。该杂志发表了从微生物到人类的有机体的实证研究以及理论工作。虽然它有着辉煌的历史，但 GENETICS 已经随着它所服务的社区而发生了变化：它不是你导师的期刊。编辑们迅速做出决定– 在大约 30 天内 – 在不牺牲该期刊长期以来所享有的卓越和学术成就的情况下。GENETICS 是一个同行评审、同行编辑的期刊，具有国际影响力和日益增加的知名度和影响力。所有的编辑决定都是通过合作做出的至少有两名从事科学家工作的编辑。GENETICS 不断创新：扩展的内容类型包括评论、评论（遗传学家当前感兴趣的问题）、观点（历史）、引物（将主要文献引入课堂）、工具箱评论、加上 YEASTBOOK、FLYBOOK 和 WORMBOOK（将于 2016 年春季推出）。对于对时间特别敏感的结果，我们会发布 COMMUNICATIONS。作为我们的一部分以服务我们的社区为使命，我们出版了主题合集，包括基因组选择、多亲群体、小鼠合作杂交和性遗传学。

Genetics is an academic journal published by the American Society of Genetics, aimed at deepening our understanding of the living world through the promotion of genetics. Since its inception in 1916, Genetics has published high-quality original research showcasing new discoveries related to genetics and genomics. The journal features empirical studies and theoretical work on organisms ranging from microbes to humans. While it has a rich history, Genetics has evolved with the community it serves: it is not your mentor's journal. The editors make swift decisions—typically within about 30 days—without compromising the excellence and academic achievements that the journal has long enjoyed. Genetics is a peer-reviewed, editor-reviewed journal with international influence and an increasing reputation and impact. All editorial decisions are made collaboratively by at least two editors engaged in scientific work. Genetics continuously innovates, expanding its content types to include reviews, commentaries on current issues of interest to geneticists, historical perspectives, primers that introduce key literature, toolbox reviews, as well as YEASTBOOK, FLYBOOK, and WORMBOOK (to be launched in Spring 2016). For results that are particularly time-sensitive, we publish communications. As part of our mission to serve our community, we publish thematic collections on topics such as genomic selection, multiparental populations, mouse collaborative crosses, and sexual genetics.

《Genetics》是由美国遗传学会出版的一本学术期刊，旨在通过促进对遗传学的理解，深化我们对生命世界的认识。自1916年以来，《Genetics》发表了高质量的原创研究，展示了与遗传学和基因组学相关的新发现。该期刊涵盖了从微生物到人类的实证研究以及理论工作。尽管拥有辉煌的历史，《Genetics》已随着服务的社区而不断演变：它不是你导师的期刊。编辑们迅速做出决定，通常在约30天内，且不牺牲该期刊长期以来享有的卓越和学术成就。《Genetics》是一个具有国际影响力的同行评审、同行编辑的期刊，知名度和影响力日益增加。所有编辑决定均由至少两名从事科学研究的编辑通过合作做出。《Genetics》不断创新，扩展了内容类型，包括评论、遗传学家当前感兴趣的问题的评论、历史观点、引导文献的引导、工具箱评论，以及YEASTBOOK、FLYBOOK和WORMBOOK（将于2016年春季推出）。对于时间特别敏感的结果，我们会发布通讯。作为服务社区的一部分，我们出版了主题合集，包括基因组选择、多亲群体、小鼠合作杂交和性遗传学。

Category	Quartile
生物学	3
生物学, 遗传学	3

Robust sex determination in the Caenorhabditis nigoni germ line

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