ESTABLISHMENT OF SPERMATOGENESIS FOLLOWING TESTICULAR TISSUE ECTOPIC XENOGRAFTING IN ALPACA
Elzawam, Aymen Z.
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Sperm production depends on development, puberty and germ cell differentiation. Puberty age of alpaca varies and little is known of factors regulating this process. The species is also known for a high incidence of congenital testicular abnormalities and consequently poor fertility. Studies included in this dissertation were designed to investigate male development and testis function in alpaca. The endocrinological aspects of puberty were investigated through analysis of testosterone and estrogen in blood samples collected before after treatment with human chorionic gonadotropin (hCG, Chorulon®, 3000 IU, IV). Administration of hCG to 60 males aged from 6 to 60 months resulted in a 2 to 4.5 fold increase (P < 0.05) in serum testosterone concentration after 2 hours. Testicular sensitivity to hCG resulted in rapid response in males between 9 and 14 months of age and a second increased responsiveness after 21 months of age suggesting biphasic Leydig cell differentiation. To investigate the cellular aspects of testicular development, 104 male alpacas were castrated and testicular tissues were processed for morphometric and gene expression analysis. The males were divided into five age groups based on months of age: 1.6-10, 2. 11-15, 3. 16-20, 4. 21-24, and 5. over 25. Morphological assessment in these groups was carried out by counting different cell types, seminiferous epithelium development and testosterone concentration. Gene expression analysis suggested that germ cell differentiation is the most variable aspect of alpaca testis development. Last, pieces of alpaca testis were xenografted onto nude mice and harvested after 24 weeks. Evaluation of germ cell differentiation was achieved by histological examination of grafts and analysis of mouse blood testosterone. Prepubertal animals at 6 to 10 months were selected as donors for testis tissue xenografting. Alpaca testis xenografts produced testosterone and elongated spermatids. Graft survival ranged from 79.1% to 83.3% and grafts with elongating spermatids were 6.8, 4.3, 1.1, 1.1 and 1.7% from donor alpacas aged 6, 7, 8,9,10 months, respectively. These studies suggest that variations of alpaca testis development are associated with Leydig cell maturation and germ cell differentiation. Novel approaches such as testis xenografting can be utilized to investigate factors regulating these processes.