Ovarian follicle development is a crucial physiological process in animal reproduction, which occurs throughout the lifespan. Chicken is a widely recognized model for investigating ovarian development of humans due to its prolific ovulation [1], as well as an ideal model for studying human ovarian diseases, as it is the only non-human animal known to develop ovarian tumors [2]. Disordered ovarian follicle development is closely related to ovarian diseases, including Polycystic Ovary Syndrome (PCOS) [3] and Premature Ovarian Failure (POF) [4], which leads to a significant impact on women's health. On the other hand, the development of chicken ovarian follicles is also important due to its egg production for human protein foods. Thus, it is essential to investigate the underlying mechanisms of ovarian follicle development to improve chicken reproductive performance and provide a new therapeutic strategy for ovarian disease occurrence.

GCs are critical components of follicles, and they not only maintain the normal growth of the follicle but also control follicle atresia [5]. The proliferation and apoptosis of GCs play a vital role in ovarian follicular development. Recent studies have shown that endogenous RNAs, including microRNAs (miRNAs) and circRNAs, are extensively involved in GCs development in different species. For example, CiRS-126 represses GCs proliferation through the miR-21-PDCD4-ROS axis in a PCOS model [6], while circular RNA aplacirc_13267 promotes GCs apoptosis by targeting apla-miR-1-13 in ducks [7]. Additionally, circRNAs can regulate steroid hormone synthesis and secretion in GCs, thereby further participating in ovarian follicle development [8,9].

The RPS19 gene encodes a ribosomal protein that forms an essential part of the small 40S subunit of ribosomes. Reports indicate that mutations in RPS19 lead to Diamond-Blackfan anemia, a type of erythropenia [10], suggesting that the gene is involved in the control of cell proliferation in addition to its ribosomal function. Moreover, differential expression of RPS19 during tilapia gonad development suggests a potential role in animal reproduction [11]. Importantly, an increase in a circular RNA originating from the RPS19 gene, circRPS19, was observed during chicken ovarian follicle maturation [12], while RPS19 messenger RNA expression did not differ significantly during follicle development [13]. We thus hypothesize that circRPS19 significantly affects the control of ovarian follicle development in chickens. Accordingly, this study aims to investigate the potential involvement of circRPS19 in the proliferation and steroid hormone synthesis of chicken GCs, to further elucidate its role in chicken ovarian follicle development.