Germline Specific Expression of a vasa Homologue Gene in the Viviparous Fish Black Rockfish (Sebastes schlegelii) and Functional Analysis of the vasa 3' Untranslated Region.

Li Zhou,Qinghua Liu,Haixia Zhao,Zongcheng Song,Jun Li,Jiachen Yu,Xueying Wang,Shuran Du,Yanfeng Wang,Lele Wu,Tengfei Du

doi:10.3389/fcell.2020.575788

Abstract

Germ cells play a key role in gonad development. As precursors, primordial germ cells (PGCs) are particularly important for germline formation. However, the origination and migration patterns of PGCs are poorly studied in marine fish, especially for viviparous economic species. The vasa gene has been widely used as a germ cell marker to identify a germline because vasa RNA is a component of germ plasm. In this study, we described the expression pattern of black rockfish (Sebastes schlegelii) vasa (Ssvas) in gonadal formation and development by in situ hybridization. The results showed that Ssvas failed in localization at the cleavage furrows until the late gastrula stage, when PGCs appeared and migrated to the genital ridge and formed elongated gonadal primordia at 10 days after birth. This study firstly revealed the PGCs origination and migration characteristics in viviparous marine fish. Furthermore, we microinjected chimeric mRNA containing EGFP and the 3′untranslated region (3′UTR) of Ssvas into zebrafish (Danio rerio) and marine medaka (Oryzias melastigma) fertilized eggs for tracing PGCs. We found that, although Sebastes schlegelii lacked early localization, similar to red seabream (Pagrus major) and marine medaka, only the 3′UTR of Ssvas vasa 3′UTR of black rockfish was able to label both zebrafish and marine medaka PGCs. In comparison with other three Euteleostei species, besides some basal motifs, black rockfish had three specific motifs of M10, M12, and M19 just presented in zebrafish, which might play an important role in labeling zebrafish PGCs. These results will promote germ cell manipulation technology development and facilitate artificial reproduction regulation in aquaculture.

Highlights

As highly specialized cells, germ cells play a key role in germline development (Xu et al, 2010)
In phylogeny, compared to Osteriophysans species like Danio rerio, Sebastes schlegelii was closer to some Euteleostei fish, such as Thunnus orientalis, Scophthalmus maximus, Pagrus major, Oryzias latipes, and Oncorhynchus mykiss (Figure 1B)
The present study reported that the vasa identified the germline in Sebastes schlegelii

Summary

Introduction

Germ cells play a key role in germline development (Xu et al, 2010). Many maternal-effect genes such as vasa, dnd, dazl, and nanos localized in germplasm have been identified and extensively used as germ cell markers to study origination and migration of PGCs in fish (Xu et al, 2007; Lindeman and Pelegri, 2010; Yoshizaki et al, 2010; Hong et al, 2016). This reveals that the PGC migration routes and gonadal formation times vary from fish species. Under the control of the endocrine regulation and the external environment, gonads gradually develop to maturity and produce sexual gametes

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