A chromosome‐level genome of black rockfish, Sebastes schlegelii, provides insights into the evolution of live birth

Abstract

The black rockfish (Sebastes schlegelii) is a teleost in which eggs are fertilized internally and retained in the maternal reproductive system, where they undergo development until live birth (viviparity). In the present study, we report a chromosome‐level black rockfish genome assembly. High‐throughput transcriptome analysis (RNA‐seq and ATAC‐seq) coupled with in situ hybridization (ISH) and immunofluorescence reveal several candidate genes for maternal preparation, sperm storage and release, and hatching. We propose that zona pellucida (ZP) proteins retain sperm at the oocyte envelope, while genes in two distinct astacin metalloproteinase subfamilies serve to release sperm from the ZP and free the embryo from chorion at prehatching stage. We present a model of black rockfish reproduction, and propose that the rockfish ovarian wall has a similar function to the uterus of mammals. Together, these genomic data reveal unprecedented insights into the evolution of an unusual teleost life history strategy, and provide a sound foundation for studying viviparity in nonmammalian vertebrates and an invaluable resource for rockfish ecological and evolutionary research.

The Bdkrb2 Gene Family Provides a Novel View of Viviparity Adaptation in Sebastes schlegelii

“…We previously reported that the NO-sGc-cGMP signaling pathway was identi ed in WGCNA co-expression module of ovarian wall, and proposed that the rock sh ovarian wall has a similar function to the uterus of mammals [4]. The chemical messenger NO is an endothelium derived relaxing factor, which participates in the control of vasorelaxation in fetoplacental vessels [47].…”

“…In a previous study, we revealed the adaptation of black rock sh to viviparity based on both the genomic and transcriptomic evidences. We found genes related to placental development, cell adhesion, trophoblast invasion, calcium-sensing receptors, the NO-sGc-cGMP signalling pathway, and blood vessel function were co-expressed in the ovarian wall [4]. We thus hypothesized that the ovarian wall of black rock sh had the function similar to the mammalian uterus.…”

“…The time course of copulation up to birth spans about 8 months. It takes 6 months for oocytes to mature and fertilized with stored sperm in the ovary [1,4]. The gestation period is about 50 days [5,6].Contrast to mammals, where embryonic development occurs in the uterus, embryos develop in the ovary in black rock sh.…”

Transcriptome-wide identification and validation of reference genes of Black rockfish (Sebastes schlegelii) for quantitative RT-PCR

“…Embryos at six different stages (1-cell, 32-cell, blastula, gastrula, somite and pre-hatching) were collected as described in our previous study [12]. Then, they were stored at -80℃ for further use.…”

“…The black rockfish (S.schlegelii, hereafter denoted 'rockfish') evolving live birth, is a good model of teleost to study the adaption to viviparity [12]. Some studies have been carried out focusing on the genes related to development, growth, immunity, and reproduction in this group of fish [13][14][15].…”