Abstract

This study, by combining histological observation and transcriptome sequencing, systematically reveals the developmental characteristics and molecular regulatory mechanisms of the testes of one- and two-year-old Kazakh horses during the critical period of sexual maturity. In the testes of one-year-old horses, histological analysis found no obvious lumen, and the interior mainly comprised supporting cells and spermatogonia on the basement membrane. In the testes of two-year-old horses, the lumina were complete, and spermatogonia, spermatocytes, and sperm could be observed, indicating that spermatogenic function was approaching maturity. Functional enrichment analysis indicated biological processes, including multicellular organism development and cell membrane structural composition, related to the differentially expressed genes and significant enrichment of key pathways, including calcium signaling and cell adhesion molecules. The protein interaction network identified core genes, including TNF and CATSPER2 . These findings elucidate the dynamic changes in testicular development at both the tissue and molecular levels, providing theoretical references and candidate genes for genetic improvement related to reproductive performance in Kazakh horses. This study systematically elucidated the developmental characteristics and molecular regulatory mechanisms of the testis during the critical period of sexual maturation in Kazakh horses by combining histological observation of one- and two-year-old testicular tissues with transcriptomic sequencing. In the testes of one-year-old horses, no obvious lumen was observed, and the interior is mainly comprising supporting cells and spermatogonia on the basement membrane; in contrast, in the testes of two-year-old horses, the tubular lumen was complete with spermatogonia, spermatocytes, and spermatozoa, indicating that spermatogenic function had approached maturity. Transcriptome profiling identified 979 differentially expresse