Adverse conditions (oxidative stress, imbalanced lipid, glucose or calcium levels, or inflammation) induce the accumulation of abnormal proteins resulting in ER stress. The Unfolded Stress Response (UPR) is activated to restore cellular homeostasis, but severe or chronic stress results in apoptotic cell death. Uncontrolled UPR signaling promotes many human diseases (diabetes, Parkinson's, Alzheimer's, liver disease, cancer...), but nothing is known about its implication in adult male sterility. Spermatozoa production relies on Spermatogonial Stem Cells (SSC) which are maintained by self-renewal throughout life. We have shown that the clonogenic activity of SSC is drastically impaired after ER stress through differentiation entry. An HTS screen has highlighted 2 of the 3 UPR branches as being involved in the clonogenic activity of SSC in vitro. The role of these 2 UPR pathways will be further investigated in SSC cultures of mice to determine whether they are involved in the induction of cell death or in the balance between self renewal and differentiation. In treated SSC cultures, cell death, cell cycle, induction of differentiation and synergy between UPR pathways will be analyzed. As the effect of each pathway is mediated by transcriptional factors, the target genes will be characterized by RNAseq in order to identify the gene networks controlled by UPR effectors and involved in the fate of SSC. For the most relevant pathway, an in vivo study will confirm the role of the UPR effector in CSS property.