Abstract
Spermatogenesis is a highly complex developmental process that occurs primarily in seminiferous tubules of the testes and requires additional maturation steps in the epididymis and beyond. Mutations in many different genes can lead to defective spermatozoa and hence to male infertility. Some of these genes encode for ion channels and transporters that play roles in various processes such as cellular ion homeostasis, signal transduction, sperm motility, and the acrosome reaction. Here we show that germ cell–specific, but not Sertoli cell–specific, disruption of Lrrc8a leads to abnormal sperm and male infertility in mice. LRRC8A (leucine-rich repeat containing 8A) is the only obligatory subunit of heteromeric volume-regulated anion channels (VRACs). Its ablation severely compromises cell volume regulation by completely abolishing the transport of anions and osmolytes through VRACs. Consistent with impaired volume regulation, the cytoplasm of late spermatids appeared swollen. These cells failed to properly reduce their cytoplasm during further development into spermatozoa and later displayed severely disorganized mitochondrial sheaths in the midpiece region, as well as angulated or coiled flagella. These changes, which progressed in severity on the way to the epididymis, resulted in dramatically reduced sperm motility. Our work shows that VRAC, probably through its role in cell volume regulation, is required in a cell-autonomous manner for proper sperm development and explains the male infertility of Lrrc8a−/− mice and the spontaneous mouse mutant ébouriffé.
Highlights
Spermatogenesis is a highly complex developmental process that occurs primarily in seminiferous tubules of the testes and requires additional maturation steps in the epididymis and beyond
Our work shows that volume-regulated anion channels (VRACs), probably through its role in cell volume regulation, is required in a cell-autonomous manner for proper sperm development and explains the male infertility of Lrrc8a؊/؊ mice and the spontaneous mouse mutant ébouriffé
It is generally believed that VRAC is ubiquitously expressed in all vertebrate tissues and cells [11, 20, 31], which is consistent with the wide expression pattern of all LRRC8 genes gleaned from EST database analysis [21]
Summary
Head shape and the assembly of a mitochondrial sheath around the axoneme of the flagellum. The general importance of LRRC8 channels became evident from the severe phenotypes of Lrrc8aϪ/Ϫ mice, which were reported shortly after the identification of LRRC8A as an obligatory VRAC constituent [28]. These mice display high pre- and postnatal mortality, growth retardation, curly hair, and abnormalities in several tissues. The first characterization of ébouriffé mice focused on their male sterility, which was attributed to structural defects of sperm cells [29] It remains, unclear whether a complete loss of LRRC8A would have similar consequences and whether these pathologies are cellautonomous outcomes of a reduction of VRAC currents in germ cells or in Sertoli cells. Spermatozoa showed flagellar coiling or angulation, features that were previously described with abnormal cell swelling upon RVD failure [7]
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