Abstract
BackgroundAcipenser dabryanus, an endemic Chinese species, has been listed as a first-class protected animal in China. Sturgeons are among the oldest and most primitive group of existing fish in the world and occupy a special place in the evolutionary history of fish. Thus, a study of the reproduction and sex differentiation of sturgeon will be of great value for fish as well as the whole vertebrate group.MethodsIn this study, we conducted comparative analysis of the testes and ovaries transcriptomes of A. dabryanus to screen for sex-differentiation and sexual development-related genes.ResultsThe transcriptome sequencing of six cDNA libraries generated 265 million clean reads, encompassing 79 Gb of sequences. The N50 and mean length of the identified 91,375 unigenes were 1,718 and 989 bp, respectively. A total of 6,306, 9,961, 13,170, 15,484, and 23,588 unigenes were annotated in the clusters of orthologous groups, gene ontology categories, Kyoto Encyclopedia of Genes and Genomes Pathway, euKaryotic orthologous groups, and NCBI non-redundant protein databases, respectively. A total of 5,396 differentially expressed genes were found between the two sexes, with 1,938 predicted to be up-regulated in ovaries and 3,458 in testes. A total of 73 candidate genes known to be involved in sex differentiation and sexual development were searched in the transcriptome of A. dabryanus of which 52 showed significant similarity. We highlighted six genes that are differentially expressed between the two sexes and may play important roles in sex differentiation and gonad maintenance. In addition, 24,271 simple sequence repeats (SSRs) and 550,519 single-nucleotide polymorphisms (SNPs) were detected.DiscussionThis work represents the first transcriptome study comparing the ovary and testis in A. dabryanus. The putative differentially expressed genes between the gonads provide an important source of information for further study of the sex-differentiation related genes and the sex-differentiation mechanism in sturgeons. The SSRs or SNPs identified in this study will be helpful in the discovery of sex-related markers in A. dabryanus.
Highlights
Sex is regarded as the queen of problems in evolutionary biology (Lewispye & Montalban, 2015)
In 9-month-old sturgeon, gonads started to differentiate and spermatophore can be observed in testis and oogonium began to form in ovary (Figs. 1A and 1D)
The connective tissue and microvessels are rich in ovary tissue, the follicular shape is irregular and loose and oogonium can be observed inside the follicle (Figs. 1D, 1E and 1F)
Summary
Sex is regarded as the queen of problems in evolutionary biology (Lewispye & Montalban, 2015). The study of sex determination and differentiation in fish will help to reveal the formation and evolution of sex determination mechanisms of the whole vertebrate group. Considering the special evolutionary position of sturgeons, study on their reproduction and sex differentiation will be of great theoretical value for fish as well as vertebrates. Growers usually wait 3–4 years before fish are sexed via an invasive surgical examination of the gonads (Doroshov, Moberg & Van Eenennaam, 1997) This limits the effective protection and artificial propagation of A. dabryanus. A study of the reproduction and sex differentiation of sturgeon will be of great value for fish as well as the whole vertebrate group. Methods: In this study, we conducted comparative analysis of the testes and ovaries transcriptomes of A. dabryanus to screen for sex-differentiation and sexual development-related genes. The SSRs or SNPs identified in this study will be helpful in the discovery of sex-related markers in A. dabryanus
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