Importance of eIF2α phosphorylation as a protective mechanism against heat stress in mouse male germ cells.

Mammalian male germ cells are exceptionally labile to heat stress. A temporal arrest of translation is one immediate response to heat, which involves heat-induced phosphorylation of eukaryotic initiation factor 2α (eIF2α) to block the formation of the translational initiation complex. Here, we investigated the protective mechanisms against heat stress in mouse male germ cells. All known eIF2α kinases were expressed in lineage- and developmental stage-specific manners in the testis; noteworthy was the presence of Gcn2 (General control nonderepressible 2 kinase) in spermatocytes of all seminiferous tubules. Multiple eIF2α kinases are likely activated upon heat stress in male germ cells. ISRIB (Integrated stress response inhibitor) was then used to determine the events downstream of eIF2α phosphorylation. ISRIB significantly reduced the rate of stress granule formation in spermatocytes at early-stage (III-IV) seminiferous tubules, and induced a number of apoptotic germ cells at late-stage (XI-XII) seminiferous tubules near the onset of meiosis. Thus, stress granule formation is a downstream event of eIF2α phosphorylation that may not directly protect cells from apoptosis, at least in spermatocytes of seminiferous tubules in early stages. Mol. Reprod. Dev. 84: 265-274, 2017. © 2017 Wiley Periodicals, Inc.