Intercellular bridges are a conserved feature of spermatogenesis in mammalian germ cells and derive from arresting cell abscission at the final stage of cytokinesis. However, it remains to be fully understood how germ cell abscission is arrested in the presence of general cytokinesis components. The TEX14 (testis-expressed gene 14) protein is recruited to the midbody and plays a key role in the inactivation of germ cell abscission. To gain insights into the structural organization of TEX14 at the midbody, we have determined the crystal structures of the EABR [endosomal sorting complex required for transport (ESCRT) and ALIX-binding region] of CEP55 bound to the TEX14 peptide (or its chimeric peptides) and performed functional characterization of the CEP55-TEX14 interaction by multiexperiment analyses. We show that TEX14 interacts with CEP55-EABR via its AxGPPx 3 Y (Ala793, Gly795, Pro796, Pro797, and Tyr801) and PP (Pro803 and Pro804) sequences, which together form the AxGPPx 3 YxPP motif. TEX14 competitively binds to CEP55-EABR to prevent the recruitment of ALIX, which is a component of the ESCRT machinery with the AxGPPx 3 Y motif. We also demonstrate that a high affinity and a low dissociation rate of TEX14 to CEP55, and an increase in the local concentration of TEX14, cooperatively prevent ALIX from recruiting ESCRT complexes to the midbody. The action mechanism of TEX14 suggests a scheme of how to inactivate the abscission of abnormal cells, including cancer cells.TEX14 | intercellular bridges | CEP55 | germ cells | cytokinesis I ntercellular bridges are a distinct feature of spermatogenesis in mammalian germ cells. Although observations of intercellular bridges were reported more than 100 y ago, their molecular function is largely unknown and we have only recently begun to learn how they form at the molecular level. Interestingly, stable bridges have recently been recognized as providing a unique means of intercellular communication, because cytoplasmic molecules can pass through them (1). The loss of germ cell intercellular bridges disrupts spermatogenesis and causes sterility (2).The most direct method of cell-to-cell communication is to connect the separate cytosols of cells using a tunnel that allows macromolecules to pass from one cell to another. Various organisms achieve this type of direct intercellular transfer using tunneling nanotubes (3), intercellular bridges (also called ring canals) (1), and bacterial intercellular nanotubes (4). Somatic ring canals have also been found to equilibrate the levels of some proteins between connected cells in invertebrates such as Drosophila (5). Among these mechanisms, it has been shown that intercellular bridges having channels that are 0.5-3 μm in diameter are formed by the arrest of cell abscission at the final stage of cytokinesis in the germ cells of vertebrates (1).Whether the process of cell abscission is completed or not depends on the cell type. In the somatic cells of vertebrates, cell abscission occurs at the midbody (6), a structure that tethers two...
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.
Humans are occasionally exposed to extreme environmental heat for a prolonged period of time. Here, we investigated testicular responses to whole‐body heat exposure by placing mice in a warm chamber. Among the examined tissues, the testis was found to be most susceptible to heat stress. Heat stress induces direct responses within germ cells, such as eukaryotic initiation factor 2α phosphorylation and stress granule (SG) formation. Prolonged heat stress (42°C for 6 hr) also disturbed tissue organization, such as through blood‐testis barrier (BTB) leakage. Germ cell apoptosis was induced by heat stress for 6 hr in a cell type‐ and developmental stage‐specific manner. We previously showed that spermatocytes in the early tubular stages (I–VI) form SGs for protection against heat stress. In the mid‐tubular stages (VII–VIII), BTB leakage synergistically enhances the adverse effects of heat stress on pachytene spermatocyte apoptosis. In the late tubular stages (IX–XII), SGs are not formed and severe leakage of the BTB does not occur, resulting in mild apoptosis of late‐pachytene spermatocytes near meiosis. Our results revealed that multiple stress responses are involved in germ cell damage resulting from prolonged heat stress (42°C for 6 hr).
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