June 2013 (No. 2)
Relationships of serum thyroid hormones and follicle-stimulating hormone concentrations to Sertoli cell differentiation during the first wave of spermatogenesis in euthyroid ram lambs
Olutobi A. Oluwole, Pawel M. Bartlewski*, Ann Hahnel
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Canada
The main purpose of this study was to determine if temporal relationships exist between serum concentrations of free fractions of thyroxin (fT4) and triiodothyronine (fT3), follicle stimulating hormone (FSH) levels, and Sertoli cell differentiation in euthyroid ram lamb testes. Additionally, testicular thyroid hormone (TH) receptors (TRs) were identified using immunohistochemistry and Western blot analysis. Weekly testicular biopsies and jugular blood samples were collected from 12 ram lambs over the 9 weeks of study. Hormone concentrations and the numbers of dividing Sertoli cells per seminiferous tubule (ST) area were analyzed relative to chronological age of animals and the two distinctive stages of Sertoli cell differentiation: (a) tight junction/ST lumen formation and (b) the onset of support mechanisms for the development of multiple germ cell types (presence of primary spermatocytes in >95% STs). Circulating FSH concentrations increased ( p < 0.05) immediately after first detection of ST lumen and reached a nadir ( p < 0.05) just prior to the end of the first wave of spermatogenesis. A decline in both fT4 and fT3 levels (p < 0.05) occurred after Sertoli cells had formed the ST lumen and began supporting germ cell differentiation. There was a positive correlation between the numbers of proliferating Sertoli cells and serum fT4 (r = 0.51, p < 0.001) and fT3 (r = 0.52, p < 0.001) concentrations. TRs were expressed throughout the study period; however, prior to the formation of ST lumen, two isoforms were detected while only one TR isoform was present by the end of the first wave of spermatogenesis. Overall, the exit of Sertoli cells from the cell cycle that presages their final differentiation begins when THs and FSH levels are high, suggesting a permissive role of these hormones in the maturation of STs in prepubertal ram lambs.
Reproductive Biology 2013 13 2: 150–160.
* Corresponding author: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road, Guelph, ON N1G 2W1, Canada; e-mail address: firstname.lastname@example.org