Construction and differential analysis of testicular atlas between 10-week-old and 23-week-old ducks using single-cell RNA sequencing.

While spermatogenesis has been extensively characterized in mammals, its molecular underpinnings in avian species remain largely unexplored. To address this knowledge gap, we performed single-cell transcriptomic profiling of duck testes across developmental stages (10-week immature vs. 23-week mature). Our analysis generated a comprehensive cellular atlas comprising 54,702 cells, resolving eight germ cell clusters (three spermatogonia [SPG], three spermatocytes [SPC], two spermatozoa [SPT]) and nine somatic populations, including peritubular myoid cells, immune subsets (T cells, macrophages, granulocytes), endothelial cells, Leydig cells, and three Sertoli cell subtypes, each defined by unique marker gene signatures. Furthermore, novel marker genes were identified, including EXFABP for granulocyte, ARHGAP15 for T cell regulation, FDX1 specific to Leydig cells (LC), and TSSK3/TSSK2 linked to elongated spermatid formation (SPT). Notably, we identified some novel molecular markers distinguishing these populations. Pseudotemporal trajectory reconstruction of germline development revealed stage-specific enrichment of ribosome, endoplasmic reticulum protein processing, and autophagy pathways. Core regulators MRPL13, MRPL2, MRPL22, MRPS14, MRPS7 (ribosome), HSPA5 (ER stress response), and PIK3C3 (autophagy) emerged as molecular hubs showing progressive downregulation during differentiation. Comparative transcriptomic analysis of germ cells and Sertoli cells between immature (IMT) and mature (MT) testes revealed significant enrichment of the spliceosome pathway in both germ and Sertoli cells. Critical spliceosome components SNRPG, SF3B3, and SNRPF exhibited coordinated downregulation during testicular maturation, suggesting their role as negative regulators of spermatogenic progression. This study establishes the first high-resolution cellular blueprint of avian spermatogenesis, delineating regulatory networks of duck testis cell development. Our findings provide valuable datasets and mechanistic insights into the evolutionary specialization of reproductive strategies in poultry.