LncRNA RORB-IT1 Encoding a Micropeptide Regulates Progesterone Synthesis, Proliferation and Apoptosis in Chicken Granulosa Cells

Ovarian follicular development determines the egg-laying performance in chickens. Besides hormonal signaling, epigenetic and post-transcriptional regulators, long non-coding RNAs (lncRNAs) also play a vital role in follicular development. We previously identified that RAR-related orphan receptor B-intronic transcript 1 (<i>RORB-IT1</i>), a novel lncRNA located in the intron of <i>RORB</i>, was differentially expressed in chicken pre-hierarchical and hierarchical follicular granulosa cells (Post-GCs). However, it remains unknown whether <i>RORB-IT1</i> participates in regulating the development of chicken ovarian follicles. In this study, we further characterized the expression pattern of <i>RORB-IT1</i> and explored its role in regulating the progesterone synthesis, proliferation and apoptosis of chicken Post-GCs. The results showed that <i>RORB-IT1</i>, with a full length of 383 bp, exhibits a uniform distribution in both the cytoplasm and nucleus of chicken Post-GCs. <i>RORB-IT1</i> was specifically expressed in Post-GCs and upregulated by follicle-stimulating hormone (FSH), progesterone (P4) and estradiol (E2) in a dose-dependent manner. Functionally, <i>RORB-IT1</i> promoted P4 synthesis and proliferation, while inhibiting the apoptosis of Post-GCs. Furthermore, we demonstrated that <i>RORB-IT1</i> encoded a functional micropeptide exhibiting dual localization in both cytoplasmic and nuclear compartments. This micropeptide enhanced progesterone synthesis and proliferation, but paradoxically induced the apoptosis of Post-GCs when overexpressed independently. Collectively, this study uncovered the expression pattern and function of <i>RORB-IT1</i> in chicken Post-GCs and provided a theoretical basis for improving the egg-laying performance in chickens.