Unique Sertoli cell adaptations support enhanced spermatogenesis in chickens.

BACKGROUND: The cellular basis of testicular development and spermatogenesis for the extreme sperm density in chickens (100-fold higher than mammals) remains poorly defined. A comprehensive understanding of the molecular characteristics driving poultry testicular development is crucial for explaining this enhanced spermatogenic capacity. RESULTS: Here, we first established a single-cell transcriptome profile of chicken testes from hatching to maturity, identifying the dynamic transcriptional characteristics of germ cell fate transition and exploring the developmental characteristics of Sertoli cells and Leydig cells. Multi-species comparisons revealed a higher proportion of germ cells and the unique adaptations of Sertoli cells in chicken testes. Most importantly, our results demonstrated that Sertoli cells dominated in somatic composition of mature chicken testes, and proliferating Sertoli cells persisted in chicken testes even after sexual maturity, while no proliferating Sertoli cells in mammals. We also found a richer interaction network between chicken testicular cells, especially the specific activation of Sertoli cell interaction signals, such as TGF-β, BMP, EGF, and activin. These adaptations of Sertoli cells may support the spermatogenic superiority in chickens. Additionally, our results indicated that cAMP responsive element binding protein 5 (CREB5) played a crucial role in maintaining the maturation and function of chicken Sertoli cells, and circadian rhythm promoted testosterone secretion and the development of Leydig cells. CONCLUSION: Our study revealed that the sustained proliferative capacity of Sertoli cells, their enriched signaling network, and the regulatory roles of CREB5 and circadian rhythms collectively represented unique testicular adaptations in chickens. These findings may hold extraordinary significance in understanding the molecular characteristics of poultry testicular development, and provide a plausible framework for explaining enhanced spermatogenesis in poultry.