Abstract
The razor clam, Sinonovacula constricta is a commercially important bivalve in the western Pacific Ocean, yet little is known about the mechanisms of sex determination/differentiation and gametogenesis. In the present study, the comparative transcriptome analysis of adult gonads (female gonads and male gonads) was conducted to identify potential sex-related genes in S. constricta. The number of reads generated for each target library (three females and three males) ranged from 31,853,422 to 37,750,848, and 20,489,472 to 26,152,448 could be mapped to the reference genome of S. constricta (the map percentage ranging from 63.71 to 71.48%). A total of 8,497 genes were identified to be differentially expressed between the female and male gonads, of which 4,253 were female-biased (upregulated in females), and 4,244 were male-biased. Forty-five genes were identified as potential sex-related genes, including DmrtA2, Sox9, Fem-1b, and Fem-1c involved in sex determination/differentiation and Vg, CYP17A1, SOHLH2, and TSSK involved in gametogenesis. The expression profiles of 12 genes were validated by qRT-PCR, which further confirmed the reliability and accuracy of the RNA-Seq results. Our results provide basic information about the genes involved in sex determination/differentiation and gametogenesis, and pave the way for further studies on reproduction and breeding in S. constricta and other marine bivalves.
Highlights
The razor clam, Sinonovacula constricta is a marine bivalve, living in the lower to mid intertidal zones along the western Pacific Ocean coast (Morton, 1984; Wang and Xu, 1997)
By analyzing the female and male gonad transcriptome of S. constricta, we identified at least 45 sex-related genes, including DmrtA2, Sox9, Fem-1b, Fem-1c, and Beta-catenin potentially involved in sex determination or differentiation, and Vg, CYP17A1, TSSK, and SOHLH2 potentially involved in gametogenesis
Zebrafish DmrtA2 expression was restricted in developing germ cells and brain, especially in spermatogonia, spermatocytes, spermatids, and sperm cells, which suggested that DmrtA2 was potentially involved in gonadal development and spermatogenesis (Guo et al, 2004; Xu et al, 2013)
Summary
The razor clam, Sinonovacula constricta is a marine bivalve, living in the lower to mid intertidal zones along the western Pacific Ocean coast (Morton, 1984; Wang and Xu, 1997). In China, S. constricta has become one of the most commercially important cultured clam species and has huge market potential. Compared with other economically important molluscan species, S. constricta is diecious (i.e., with fixed gender; individuals do not change sex), and the gonad maturation period is from September to October (Wu and Xu, 2000). It is difficult to differentiate between female and male clams with external morphological characteristics, especially before sex maturity (Wang et al, 1993). Gonadal maturity and synchronicity cannot be estimated by appearance, yet they are important factors for successful artificial reproduction. In the artificial reproduction conditions of bivalves, the successful hatching of selected spat relies on production of gametes and embryos from synchronous breeders. The mechanisms that underlie gonad development and sex determination/differentiation in S. constricta are poorly understood, and there is no gene yet identified as an actor involved in gonad development or sex determination
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