The Forkhead Transcription Factor FOXC2 Is Required for Maintaining Murine Spermatogonial Stem Cells

Continuous spermatogenesis from puberty to old age in males relies on spermatogonial stem cells (SSCs) that possess the property of self-renewal and differentiation. The delicate balance between self-renewal and differentiation is of great importance. In mice, SSCs exist as a subpopulation of undifferentiated spermatogonia. SSCs are controlled by intrinsic molecular pathways that can be activated by extrinsic signals. Our results here first show that the expression of forkhead box C2 (FOXC2) is restricted to GFRα1-positive spermatogonia in the testis. Whole-mount immunofluorescence results reveal that FOXC2 is expressed predominately in A_s and A_pr spermatogonia. Reduction of Foxc2 gene expression by shRNA lentivirus treatment significantly impairs the maintenance of SSCs in vitro. Furthermore, knock-down of Foxc2 decreases SSC colonization to only 10.42% compared to the control by transplantation. Reverse transcription and real-time quantitative PCR gene analyses following knock-down of Foxc2 indicate that Foxc2 may act as a suppressor for SSC differentiation. Extrinsic stimuli treatments show that glial cell line-derived neurotrophic factor and retinoic acid act in opposite ways to regulate FOXC2 expression and subsequent SSC property. These results suggest that FOXC2 is a critical intrinsic regulator of SSC self-renewal and differentiation.