Transcriptional and translational dynamics during maternal-to-zygotic transition in early chicken development

Maternal-to-zygotic transition (MZT) is the critical process for the establishment of embryonic identity across vertebrates. During this period, the massive transcriptional activation, called zygotic genome activation (ZGA), is mediated by maternally stored factors, and maternal mRNA clearance by conserved zygotic microRNAs (miRNAs) occurs; however, the important transition in avian species was identified by morphologic perspectives only. In this study, we performed transcriptome analysis to examine the molecular transitions of intrauterine development in chickens. On the basis of coexpression analyses on RNA sequencing data, 2 waves of ZGA-mediated MZT were observed across the early embryonic stages and were associated with transcriptional and translational dynamics. Furthermore, definite transitions were observed according to the distinct developmental characteristics between cleavage and the area pellucida formation period in the functional analysis. Finally, epigenetic modification and the evolutionarily conserved miRNA expression suggest that certain MZT proceeds from Eyal-Giladi and Kochav stage VIII in early chicken development. We expect our study to provide an evolutionary link among vertebrates from the perspective of MZT regulation.