Abstract
Evolution of sex determination and differentiation in fishes involves a broad range of sex strategies (hermaphroditism, gonochorism, unisexuality, environmental and genetic sex determination). Annual fishes inhabit temporary ponds that dry out during the dry season when adults die. The embryos exhibit an atypical developmental pattern and remain buried in the bottom mud until the next rainy season. To elucidate genomic factors involved in the sex determination in annual fish, we explored the presence of a candidate sex-specific gene related to the cascade network in Austrolebias charrua. All phylogenetic analyses showed a high posterior probability of occurrence for a clade integrated by nuclear sequences (aprox. 900 bp) from both adults (male and female), with partial cDNA fragments of A. charrua from juveniles (male) and the dsx D. melanogaster gene. The expressed fragment was detected from blastula to adulthood stages showing a sexually dimorphic expression pattern. The isolated cDNA sequence is clearly related to dsx D. melanogaster gene and might be located near the top of the sex determination cascade in this species.
Highlights
In vertebrates different master genes acting on sex determination have been identified
Four strong master sex determining candidate genes were identified in fish: amhy in Odontesthes hatchei, gsdf in Oryzias luzonensis, amhr2 in Takifugu rubripes and sdY in Oncorhynchus mykiss
Phylogenetic analysis based on ML and Bayesian inference (BI) phylogenetic tree reconstruction (Figure 2) showed a topology with three main supported clades integrated by: 1) autosomic Dmrt1 sequences from O. latipes, O. hatcheri and Monopterus albus, Dmrt1bY from O. latipes, dmy from O. curvinotus and the isolated genomic sequences from A. charrua (70% bootstrap support); 2) Dmrt2 sequences from Danio rerio, Xiphophorus maculatus and Takifugu rubripes (100% boostrap support) and 3) Dmrt3 sequences from D. rerio and T. rubripes; Dmrt4 sequences from X. maculatus and T. rubripes genes and Dmrt5 sequences from O. latipes, X. maculatus, D. rerio and T. rubripes (63% boostrap support)
Summary
In vertebrates different master genes acting on sex determination have been identified. Sry (testis-determining gene) located in the Y chromosome is the transcription factor that triggers the testis determining cascade. The first non-mammalian master gene was discovered in fish (Oryzias latipes dmy). Four strong master sex determining candidate genes were identified in fish: amhy in Odontesthes hatchei, gsdf in Oryzias luzonensis, amhr in Takifugu rubripes and sdY in Oncorhynchus mykiss. Three of the four sex determining candidate genes (amhy, gsdf and amhr2) code for growth factors and one of their receptors demonstrating that novel actors, other than transcription factors, can be recruited at the top of the sex determination cascade (reviewed by Kikuchi and Hamaguchi, 2013)
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