GALACTOSYL RECEPTOR IN HUMAN TESTIS AND SPERM IS ANTIGENICALLY RELATED TO THE MINOR C-TYPE (CA2-DEPENDENT) LECTIN VARIANT OF HUMAN AND RAT-LIVER()

Galactosyl receptor, a cell surface Ca2+-dependent lectin with binding affinity for galactose, was evaluated by immunoblotting, immunoprecip itation, Northern blotting, and immunocytochemistry in human liver, te stis, and sperm. Polyclonal antisera raised against the minor asialogl ycoprotein receptor variant of rat hepatocytes (designated rat hepatic lectin-2/3, RHL-2/3), and its human liver-equivalent (designated H2), recognize native galactosyl receptor in the testis and sperm in immun oblotting, immunoprecipitation, and immunocytochemical experiments. An equivalent to the major hepatocyte asialoglycoprotein receptor varian t (rat RHL-1 and human H1) was not detected. Human testis and sperm ga lactosyl receptor was resolved, after immunoprecipitation and immunobl otting, as a single protein component of molecular mass 50 kD. The sin gle protein component in human testis and sperm contrasted with the do ublet nature of rat testis and sperm galactosyl receptor, consisting o f two components of molecular masses of 54 and 49 kD. Northern blottin g experiments using radiolabeled H1 and H2 cDNA probes confirmed the p resence of H2 mRNA and the lack of Hi mRNA in the human testis. Immuno cytochemical studies detected specific antigenic sites on the entire s urfaces of spermatogenic cells. However, immunoreactivity in epididyma l and ejaculated sperm was confined to head surfaces overlying the acr osome. Results from these studies, and from previous studies in the ra t, suggest that the testis/sperm galactosyl receptor is a C-type Ca2+- dependent lectin with possible roles in cell-cell interaction during s permatogenesis and sperm-zona pellucida binding at fertilization. (C) 1995 Wiley-Liss, Inc.