Temporal Transcriptome Analysis Reveals Dynamic Expression Profiles of Gametes and Embryonic Development in Japanese Flounder (Paralichthys olivaceus).

Xiancai Hao,Bo Feng,Jilun Hou,Kaiqiang Liu,Qian Wang,Changwei Shao

doi:10.3390/genes12101561

Abstract

The maternal-to-zygotic transition (MZT) is a crucial event in embryo development. While the features of the MZT across species are shared, the stage of this transition is different among species. We characterized MZT in a flatfish species, Japanese flounder (Paralichthys olivaceus). In this study, we analyzed the 551.57 GB transcriptome data of two types of gametes (sperms and eggs) and 10 embryo developmental stages in Japanese flounder. We identified 2512 maternal factor-related genes and found that most of those maternal factor-related genes expression decreased at the low blastula (LB) stage and remained silent in the subsequent embryonic development period. Meanwhile, we verified that the zygotic genome transcription might occur at the 128-cell stage and large-scale transcription began at the LB stage, which indicates the LB stage is the major wave zygotic genome activation (ZGA) occurs. In addition, we indicated that the Wnt signaling pathway, playing a diverse role in embryonic development, was involved in the ZGA and the axis formation. The results reported the list of the maternal genes in Japanese flounder and defined the stage of MZT, contributing to the understanding of the details of MZT during Japanese flounder embryonic development.

Highlights

The occurrence of vertebrate animals begins with the zygote by the fertilization of egg and sperm, and in this process, the egg and sperm each provide a set of chromosomes [1]
The maternal factor degradation occurred at the 2-cell stage of embryonic development, and the minor wave of zygotic genome activation (ZGA) was detected in 1-cell embryos
The pou5f1 and nanog are responsible for the clearance of maternal messenger RNA (mRNA), which activates zygotic gene expression during the maternal-to-zygotic transition (MZT) [11,38], implying that nanog and pou5f1 may be involved in the elimination of maternal gene products in Japanese flounder

Summary

Introduction

The occurrence of vertebrate animals begins with the zygote by the fertilization of egg and sperm, and in this process, the egg and sperm each provide a set of chromosomes [1]. The egg does not immediately start the transcription of the zygotic genome until the completion of one to more than a dozen mitosis [2]. The maternal factor degradation occurred at the 2-cell stage of embryonic development, and the minor wave of ZGA was detected in 1-cell embryos. In Drosophila, maternal gene products were degraded immediately after egg activation. When the embryo is divided into the 13th division cycle (blastula stage), the major wave of ZGA occurs, and the maternal gene products are degraded significantly [3]. The stage of elimination of maternal gene products and large-scale zygotic activation occurs in the 10th division cycle (blastula stage) in zebrafish [14,15]

Methods

Results

Discussion

Conclusion