RESUMO
Testicular cell proliferation and differentiation is critical for development of normal testicular function and male reproductive maturity. The objective of the current study was to evaluate histoarchitecture and expression of genes marking specific cells and important functions as well as testosterone production of the developing goat testes. Testes were harvested from Alpine bucks at 0, 2, 4, 6, and 8 mo of age (n = 5/age group). Paired testes weight increased from 2 to 4 (P < 0.001) and 4 to 6 mo (P < 0.01). The greatest increases in seminiferous tubule and lumen diameters and height of the seminiferous epithelium occurred between 2 and 4 mo (P < 0.001). Genes expressed in haploid germ cells (Protamine1 [PRM1], Outer Dense Fiber protein 2 [ODF2], and Stimulated by Retinoic Acid gene 8 [STRA8]) increased dramatically at the same time (P < 0.001). Expression of other genes decreased (P < 0.05) during testicular maturation. These genes included P450 side chain cleavage (CYP11A1), Sex determining region Y-box 9 (SOX9), Insulin-like Growth Factor 1 Receptor (IGF1R), and Heat Shock Protein A8 (HSPA8). The Glutathione S-Transferase A3 (GSTA3) gene, whose product was recently recognized as a primary enzyme involved in isomerization of androstenedione in man and livestock species including goats, sheep, cattle, pigs, and horses, uniquely peaked in expression at 2 mo (P < 0.05). Follicle-Stimulating Hormone Receptor (FSHR) mRNA abundance tended to steadily decrease with age (P = 0.1), while Luteinizing Hormone Receptor (LHCGR) mRNA abundance in testes was not significantly different across the ages. Testosterone content per gram of testicular tissue varied among individuals. However, testosterone content per testis tended to increase at 6 mo (P = 0.06). In conclusion, major changes in cellular structure and gene expression in goat testes were observed at 4 mo of age, when spermatogenesis was initiated. Male goats mature rapidly and represent a good model species for the study of agents that enhance or impair development of testicular functions.