Septins are polymerizing GTP binding proteins required for cortical organization during cytokinesis and other cellular processes. A mammalian septin gene Sept4 is expressed mainly in postmitotic neural cells and postmeiotic male germ cells. In mouse and human spermatozoa, SEPT4 and other septins are found in the annulus, a cortical ring which separates the middle and principal pieces. Sept4-/- male mice are sterile due to defective morphology and motility of the sperm flagellum. In Sept4 null spermatozoa, the annulus is replaced by a fragile segment lacking cortical material, beneath which kinesin-mediated intraflagellar transport stalls. The sterility is rescued by injection of sperm into oocytes, demonstrating that each Sept4 null spermatozoon carries an intact haploid genome. The annulus/septin ring is also disorganized in spermatozoa from a subset of human patients with asthenospermia syndrome. Thus, cortical organization based on circular assembly of the septin cytoskeleton is essential for the structural and mechanical integrity of mammalian spermatozoa.

SLC15A4 is a lysosome-resident, proton-coupled amino-acid transporter that moves histidine and oligopeptides from inside the lysosome to the cytosol of eukaryotic cells. SLC15A4 is required for Toll-like receptor 7 (TLR7)- and TLR9-mediated type I interferon (IFN-I) productions in plasmacytoid dendritic cells (pDCs) and is involved in the pathogenesis of certain diseases including lupus-like autoimmunity. How SLC15A4 contributes to diseases is largely unknown. Here we have shown that B cell SLC15A4 was crucial for TLR7-triggered IFN-I and autoantibody productions in a mouse lupus model. SLC15A4 loss disturbed the endolysosomal pH regulation and probably the v-ATPase integrity, and these changes were associated with disruption of the mTOR pathway, leading to failure of the IFN regulatory factor 7 (IRF7)-IFN-I regulatory circuit. Importantly, SLC15A4's transporter activity was necessary for the TLR-triggered cytokine production. Our findings revealed that SLC15A4-mediated optimization of the endolysosomal state is integral to a TLR7-triggered, mTOR-dependent IRF7-IFN-I circuit that leads to autoantibody production.

SummaryIncreasing demand for clinical retinal degeneration therapies featuring human ESC/iPSC-derived retinal tissue and cells warrants proof-of-concept studies. Here, we established two mouse models of end-stage retinal degeneration with immunodeficiency, NOG-rd1-2J and NOG-rd10, and characterized disease progress and immunodeficient status. We also transplanted human ESC-derived retinal sheets into NOG-rd1-2J and confirmed their long-term survival and maturation of the structured graft photoreceptor layer, without rejection or tumorigenesis. We recorded light responses from the host ganglion cells using a multi-electrode array system; this result was consistent with whole-mount immunostaining suggestive of host-graft synapse formation at the responding sites. This study demonstrates an application of our mouse models and provides a proof of concept for the clinical use of human ESC-derived retinal sheets.

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Docosahexaenoic acid (DHA) is one of the essential ω-3 polyunsaturated fatty acids with a wide range of physiological roles important for human health. For example, DHA renders cell membranes more flexible and is therefore important for cellular function, but information on the mechanisms that control DHA levels in membranes is limited. Specifically, it is unclear which factors determine DHA incorporation into cell membranes and how DHA exerts biological effects. We found that lysophosphatidic acid acyltransferase 3 (LPAAT3) is required for producing DHA-containing phospholipids in various tissues, such as the testes and retina. In this study, we report that LPAAT3-KO mice display severe male infertility with abnormal sperm morphology. During germ cell differentiation, the expression of LPAAT3 was induced, and germ cells obtained more DHA-containing phospholipids. Loss of LPAAT3 caused drastic reduction of DHA-containing phospholipids in spermatids that led to excess cytoplasm around its head, which is normally removed by surrounding Sertoli cells via endocytosis at the final stage of spermatogenesis. In vitro liposome filtration assay raised the possibility that DHA in phospholipids promotes membrane deformation that is required for the rapid endocytosis. These data suggest that decreased membrane flexibility in LPAAT3-KO sperm impaired the efficient removal of sperm content through endocytosis. We conclude that LPAAT3-mediated enrichment of cell membranes with DHA-containing phospholipids endows these membranes with physicochemical properties needed for normal cellular processes, as exemplified by spermatogenesis.