Abstract
Simple Summarydmy is considered to be the male-determining gene in Japanese medaka (Oryzias latipes) and Hainan medaka (Oryzias. curvinotus), both of which have the XX/XY sex-determination system. Here, we found a group of medaka in the Sanya River (named SY-medaka) and confirmed that SY-medaka belongs to O. curvinotus by morphological characteristics and mitochondrial phylogenetic analysis. Through genetic sex identification, genome re-sequencing and gonadal transcriptome analysis, it was preliminary confirmed that SY-medaka did not contain dmy. Our results provide a basis for further studies of the mechanism underlying sex determination in Oryzias and functional genomics and reproduction biology in O. curvinotus.Hainan medaka (Oryzias curvinotus) is distributed in the coastal waters of the South China Sea and is able to adapt to a wide range of salinities. In this study, we characterized O. curvinotus in Sanya River (SY-medaka), which lacks dmy (a male sex-determining gene in O. latipes and O. curvinotus). In a comparison of SY-medaka and Gaoqiao medaka (GQ-medaka), the morphological difference between the two populations does not reach the subspecies level and they can be considered two geographic populations of O. curvinotus. A mitochondrial cytochrome oxidase subunit I (CoI) sequence alignment showed that the sequence identities between SY-medaka and other geographic populations of O. curvinotus are as high as 95%. A phylogenetic analysis of the mitochondrial genome also indicated that SY-medaka belongs to O. curvinotus. Molecular marker-based genetic sex assays and whole genome re-sequencing showed that SY-medaka does not contain dmy. Further, in RNA-Seq analyses of the testis and ovaries of sexually mature SY-medaka, dmy expression was not detected. We speculate that high temperatures resulted in the loss of dmy in SY-medaka during evolution, or the lineage has another sex-determining gene. This study provides a valuable dataset for elucidating the mechanism underlying sex determination in Oryzias genus and advances research on functional genomics or reproduction biology in O. curvinotus.
Highlights
In addition to dmy, which acts as a male sexdetermining gene in O. latipes [3,4], gsdfy is a sex-determining gene in O. luzonensis [10], and sox3 serves as a sex-determining gene in O. dancena, O. marmoratus, and O. profundicola [30,57,58]
In addition to dmy, which acts as a male sexspecific molecular markers and whole genome re-sequencing indicated that the SY-medaka determining gene in O. latipes [3,4], gsdfy is a sex-determining gene in O. luzonensis [10], genome lacks dmy
We completed the first RNA-Seq analysis of the testis and ovary and sox3 serves as a sex-determining gene in O. dancena, O. marmoratus, and O. profunof SY-medaka and identified numerous differentially expressed genes (DEGs) related to sex determination and gonadal dicola [30,57,58]
Summary
O. curvinotus employs a XX/XY sex chromosome system and has the sex-determining gene dmy [3,4,5]. It has the potential to become a model for studies of sex determination and differentiation in marine fish. Various sex-determining genes in fish have been identified, including dmy RNA-seq is a rapid method to obtain gene expression data in the absence of sequenced genomes [13]. This approach has been used to identify sex-related genes and for transcriptome profiling in relation to gonadal development and gametogenesis in fish, including Oreochromis niloticus [14], Scatophagus argus [15], and Sillago sihama [16]. We found a population of medaka (named SY-medaka) in the Sanya River, southern Hainan province, which is suspected to be O. curvinotus
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