Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation of a Doublesex Gene in the Sex-Determining Pathway

Abstract

Sex-determining mechanisms are diverse among animal lineages and can be broadly divided into two major categories: genetic and environmental. In contrast to genetic sex determination (GSD), little is known about the molecular mechanisms underlying environmental sex determination (ESD). The Doublesex (Dsx) genes play an important role in controlling sexual dimorphism in genetic sex-determining organisms such as nematodes, insects, and vertebrates. Here we report the identification of two Dsx genes from Daphnia magna, a freshwater branchiopod crustacean that parthenogenetically produces males in response to environmental cues. One of these genes, designated DapmaDsx1, is responsible for the male trait development when expressed during environmental sex determination. The domain organization of DapmaDsx1 was similar to that of Dsx from insects, which are thought to be the sister group of branchiopod crustaceans. Intriguingly, the molecular basis for sexually dimorphic expression of DapmaDsx1 is different from that of insects. Rather than being regulated sex-specifically at the level of pre–mRNA splicing in the coding region, DapmaDsx1 exhibits sexually dimorphic differences in the abundance of its transcripts. During embryogenesis, expression of DapmaDsx1 was increased only in males and its transcripts were primarily detected in male-specific structures. Knock-down of DapmaDsx1 in male embryos resulted in the production of female traits including ovarian maturation, whereas ectopic expression of DapmaDsx1 in female embryos resulted in the development of male-like phenotypes. Expression patterns of another D. magna Dsx gene, DapmaDsx2, were similar to those of DapmaDsx1, but silencing and overexpression of this gene did not induce any clear phenotypic changes. These results establish DapmaDsx1 as a key regulator of the male phenotype. Our findings reveal how ESD is implemented by selective expression of a fundamental genetic component that is functionally conserved in animals using GSD. We infer that there is an ancient, previously unidentified link between genetic and environmental sex determination.

Sex chromosome evolution in moths and butterflies

“…Instead, the male-specific BmIMP (B. mori homologue of IGF-II mRNA binding protein) together with BmPSI (B. mori homologue of P-element somatic inhibitor) are known to regulate splicing of Bmdsx . Orthologs of dsx with sexspecific splicing are known from all investigated insects and even from a crustacean, Daphnia magna (Kato et al 2011). The sex-specific Bmdsx transcripts code for two protein isoforms, a female form, BmDSXF, and a male form, BmDSXM.…”

Molecular cloning, characterization and expression analysis of a Doublesex gene from Daphnia carinata (Crustacea: Cladocera) during different reproductive stages

“…The carapace is equivalent to the carapace of other crustaceans, which cannot only be used to protect thoracic limbs, which lose the ability to move and become the tool of food intake, but can also be used to incubate their young (Shi, 2000). Some studies on the Dsx gene suggest that Dsx expression affects organ formation (Fujii and Shimada, 2007;Kato et al, 2011). Therefore, visible expression in such important organs could suggest a regulatory role of DapcaDsx2 in the growth and development of D. carinata.…”

“…However, most of the studies focused on temperature, food, population density, metabolites, and other external environmental factors (Martinez et al, 1994;Alekseev and Lampert, 2001;Pedrozo and Bohrer, 2003). Previously, Kato et al (2011) identified two Doublesex (Dsx) genes (DapmaDsx1 and DapmaDsx2) from a freshwater branchiopod crustacean, Daphnia magna. And Toyota et al (2013) …”

Endocrinology: Advances through omics and related technologies

“…Further supporting the Daphnia model, researchers from Japan (Kato et al, 2011) used Daphnia to reveal how environmental sex determination is implemented by selective expression of a fundamental genetic component that is functionally conserved in animals using genetic sex determination, inferring that there is an ancient link between genetic and environmental sex determination.…”