Sexually Dimorphic Expression of vasa Isoforms in the Tongue Sole (Cynoglossus semilaevis)

Zhongkai Wang,Yan Sun,Quanqi Zhang,Jinning Gao,Xiaomeng Wu,Jie Qi,Zhigang Wang,Huayu Song,Haiyang Yu,László Orbán

doi:10.1371/journal.pone.0093380

Abstract

The vasa gene encodes an ATP-dependent RNA helicase of the DEAD box protein family that functions in a broad range of molecular events involving duplex RNA. In most species, the germline specific expression of vasa becomes a molecular marker widely used in the visualization and labeling of primordial germ cells (PGCs) and a tool in surrogate broodstock production through PGC transplantation. The vasa gene from tongue sole (Cynoglossus semilaevis) was characterized to promote the development of genetic breeding techniques in this species. Three C. semilaevis vasa transcripts were isolated, namely vas-l, vas-m, and vas-s. Quantitative real-time PCR results showed that C. semilaevis vasa transcripts were prevalently expressed in gonads, with very weak expression of vas-s in other tissues. Embryonic development expression profiles revealed the onset of zygotic transcription of vasa mRNAs and the maternal deposit of the three transcripts. The genetic ZW female juvenile fish was discriminated from genetic ZZ males by a pair of female specific primers. Only the expression of vas-s can be observed in both sexes during early gonadal differentiation. Before PGCs started mitosis, there was sexually dimorphic expression of vas-s with the ovary showing higher levels and downward trend. The results demonstrated the benefits of vasa as a germline specific marker for PGCs during embryonic development and gonadal differentiation. This study lays the groundwork for further application of C. semilaevis PGCs in fish breeding.

Highlights

DEAD (Asp–Glu–Ala–Asp) box protein families are ATPdependent RNA helicases present in almost all organisms
Molecular characterization of three vasa isoforms A longer 1232 bp cDNA fragment containing the two contigs that was screened from the C. semilaevis transcriptome was obtained using scaf-FW/RV primers
Similar to the studies in European sea bass [12], Senegalese sole [13], and winter flounder [74], we proposed that the total length (TL) of the juveniles has more pronounced effect on gonadal differentiation than the teleost age. quantitative real-time PCR (qRT–PCR) results indicated that only the vas-s transcript can be detected during early gonadal differentiation

Summary

Introduction

DEAD (Asp–Glu–Ala–Asp) box protein families are ATPdependent RNA helicases present in almost all organisms. Since the first isolation of the Drosophila vasa gene [3], vasa-like genes have been identified from invertebrates (e.g., hydra [2], planarian [4], nematode [5], and ascidian [6]) to vertebrates (e.g., Xenopus [7], chicken [8], mouse [9], and human [10]). With these observations, recent studies have revealed that the vasa gene and its products are restricted to the germ cell lineage in most species. Extragonadal vasa expression was reported in teleosts, such as rainbow trout [11], European sea bass [12], and Senegalese sole [13]

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