Variation And Signification Of Glial Cell Line-derived Neurotrophic Factor (GDNF) And GDNF Family Receptor-alpha 1(GFRα1) Gene Expression In The Recovery Of Spermatogenesis Of Busulfan-treated Mice

Objective: To evaluate the variation and signification of glial cell line-derived neurotrophic factor(GDNF) and GDNF family receptor alpha 1 (GFR1) gene expression in the recovery of mice's spermatogenesis, and their relation to the self-renewal and differation of spermatogonial stem cells.Methods: Adult kunming mice were injected introperitoneally with two doses of busulfan (10mg/kg bodyweight) 24 days apart so as to establish the recovery spermotogenesis model. Testis were harvested pre- injection and 1 week,2 weeks,3 weeks, 4 weeks, 6 weeks, 8 weeks , 10 weeks after the second injection. Morphological studies of spermatogonia were observed by light and electron microscopy, GDNF mRNA and GFR 1 mRNA were measured by semi-quaantitative reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization.Results: The surviving single A spermatogonia underwent a phase of active self-renewal in 1-2 weeks after the second injection, it's number increased. Type B spermatogonia appeared and the paired , aligned spermatogonia can been observed by electron microscopy in 3-4 weeks after the second injection, spermatogonia appeared in groups in the seminiferous epithelia. Primary spermatocyte and round spermatids appeared in 6~8 weeks. Normal spermatogenesis was fully recovered on seminiferous tubules in the 10 week. The expression of GDNF mRNA and GFR1 mRNA after the second injection increased in 1~2 weeks, they reached their peaks at 2 weeks (113.1 19.29% and 104.72 + 24.4%; P<0.05 and P<0.05 vs pre-injection); their expression reduced in 3-4 weeks and reached their valleies at 4 weeks (16.5 4.62% and 20.77 4.25%, P<0.01 vs pre-injection), then increased gradually and recovered to their baseline values at the 8th week after the second injection. The GDNF mRNA was expressed by sertoli cells and the GFR1 mRNAwas expressed by undifferentiated spermatogonia. The expression of GFR ?1 mRNA was postive associated with the expression of GDNF mRNA, r=0.834.Conclusions: The single A spermatogonia is the spermatogonial stem cell in mouse, the self-renewal and differentiation of spermatogonial stem cells abide by Huckin model, and their process can been divided into three phases in the recovery of mice's spermatogenesis: (1) active self-renewal, (2) active differentiation, (3) balance of self-renewal and differentiation. The bodies have much greater potential to regulate stem cell self-renewal and differentiation. The dosage of GDNF produced by sertoli cells regulates the direction of the stem cells.