Looking both ways: new research on old theories

times of excitement when an unexpected discovery spurs one to more exploration and discovery. One of his such moments was that despite its three macroscopical anatomical divisions and 10 histological, connective tissue-defined segments, the mouse epididymis showed unexpectedly six major clusters of gene activity. The location of gene expression did not correspond to the histological segments, as had been speculated from his own work on the possibly restrictive barriers to growth factors of connective tissue septa, but rather overlapped them. Taking a clue from this reappraisal of current knowledge, he also urged us to continue to challenge dogma. In the remaining meeting, work was presented on sperm proteins that undergo changes during the maturation process. Mark Baker’s work5 on the fertility-related testicular sperm protein IZUMO1 showed posttranslational modification involving glycosylation, which, when prevented by point mutation, leads to subfertility, with parallel changes to the protein’s location on the equatorial segment, as a sperm-egg interaction interface. Its phosphorylation is related to a testis-specific kinase, and its degradation is dipeptidase-related. The receptors for IZUMO1 on eggs are CD9 and Juno, of which Juno is shed postfusion, an event preventing polyspermy. To date, the protein has not yet been related to human infertility. Paty Cuasnicú6 summed up the history of the early-discovered secreted epididymal protein known then as protein D/E, but now as a member of the CRISP family. Various CRISP proteins are produced in the epididymis, with Crisp1 being involved in capacitation, sperm-zona binding and sperm-egg fusion. Crisp1 is both loosely attached by ionic forces and dependent on concentrations of zinc, when it may function as a decapacitation factor, and as a tightly attached GPI-anchored form that moves to the equatorial segment upon the acrosome reaction, when it may be involved in egg interactions via its N terminal 12 amino acids. A relationship to fertility has been shown by mouse knockouts of Crisp1 (leading to reduced egg interaction if cumulus-free, but not in-cumulus, eggs are used) and of Crisp4 (the males are fertile but their spermatozoa exhibit lower binding to the zona pellucida). Immunization of male monkeys with an antihuman CRISP1 leads to reversible infertility. Julia Dorin7 presented her lab’s. work on the large family of β-defensins; antimicrobials which interact with immune cells and which are present at high expression in the epididymis. These proteins are involved in sperm maturation since selective deletion of a cluster of defensin genes in mice produces a low siring rate, but infertility after several generations of back-crossing. In the latter defensin cluster-free animals, epididymal histology and sperm numbers appeared normal, but the spermatozoa showed reduced motility, precocious capacitation, spontaneous acrosome reactions, and an inability to bind to oocytes. Flagellar fragility indicated by decapitated spermatozoa confirmed a major role of defensins in male fertility. Human infertility may also reflect defensin abnormalities since men with a frame-shift mutation in DEFB126 have low paternity, and infertile men with low sperm motility have low amounts of sperm human β-defensin 1. Several papers presented new data on the forms of epididymosomes and the modes of transfer of their cargo to spermatozoa. Patricia Martin‐DeLeon8 has continued her study of hydrophobic, GPI-linked proteins of epididymal origin on the sperm surface by demonstrating transfer by vesicular and nonvesicular routes. Membrane-bound epididymosomes dock on the sperm surface whereas lipid carriers in the membrane-free fluid fractions mediate direct insertion; the latter transfer process being more efficient. Looking both ways: new research on old theories