Transcriptome Sequencing and Differential Analysis of Testes in One- and Two-Year-Old 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 expressed genes (DEGs), with 209 up-regulated genes, including CYP11A1 and CATSPER2, and 770 down-regulated genes, including CD9. Gene Ontology (GO) annotation indicated primary enrichment of DEGs in biological processes related to multicellular organism development, cell membrane composition, and ion binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed significant enrichment of DEGs in the calcium signaling pathway, cell adhesion molecules, and neuroactive ligand–receptor interaction, among other key pathways. Protein–protein interaction (PPI) network analysis further highlighted core genes, including TNF, CATSPER2, and CDH13. Validation by RT-qPCR confirmed the reliability of the RNA-Seq data. Our findings reveal the dynamics of testicular development in Kazakh horses through histological and molecular analyses, thereby providing a theoretical framework and candidate genes to further elucidate regulatory mechanisms and guide genetic improvement in reproductive traits.