Whole-Transcriptome Landscape Deciphers a ceRNA-Mediated “De-Repression–Activation” Circuit Governing Continuous Estrus in Ovine

Abstract

Simple Summary Seasonal breeding restricts lamb production in many parts of the world, limiting the profitability and flexibility of sheep farming. Small Tail Han sheep, a Chinese breed that reproduces year-round, provide a valuable opportunity to understand how the ovary controls continuous cycling. In this study, we compared ovarian gene expression between Small Tail Han sheep and seasonally breeding Ujumqin sheep during both estrus and diestrus. Our results show that Small Tail Han ovaries change the expression of over 1800 genes between the two cycle stages, while Ujumqin ovaries change only 23—an 82-fold difference. This suggests that year-round breeders maintain highly flexible ovarian transcription, whereas seasonal breeders actively restrict it. We further identified two classes of regulatory molecules, termed “brake-releasers” and “accelerators,” that work together to control cycle transitions. Three key regulators—miR-199a-5p, miR-204-3p and miR-199b—emerged as central hubs linking these two systems. These findings shift the focus from single gene mutations to broader regulatory networks, offering new targets for breeding sheep that reproduce more consistently. This knowledge could help farmers reduce seasonal production gaps, improve lamb supply throughout the year, and enhance the resilience of sheep operations under changing environmental conditions.