CHARACTERIZATION OF THE HEPATIC ASIALOGLYCOPROTEIN RECEPTOR IN RAT LATE-STAGE SPERMATIDS AND EPIDIDYMAL SPERM

Northern blot analysis of rat testicular (Te) poly(A)(+)RNA reveals th at a transcript homologous to the major form of the asialoglycoprotein receptor (ASGP-R), designated RHL-1, is expressed as early as one wee k postnatally and that steady-state levels are approx. 8-times higher in the Te of an 8-week-old rat (sexually mature) as compared to an 84- week-old rat (aged). Partial cDNAs encoding RHL-1 and the minor form o f the ASGP-R, designated RHL-2/3, have been cloned from two rat Te/epi didymal (Ep) cDNA libraries and rat Te poly(A)(+)RNA. Sequence analysi s of the Te/Ep RHL-1 cDNA and the Te/Ep RHL-2/3 cDNA indicates that th ese cDNAs are identical to the forms expressed in rat liver. Western b lot analysis demonstrates the presence of a 49-kDa Te/Ep RHL-1-related protein band and a 54-kDa Te/Ep RHL-2/3-related protein band in both rat Te membrane fractions (MF) and rat Ep sperm MF. The RHL-1-related protein has been localized to late-stage Te spermatids at the time of release from the seminiferous tubules and to Ep sperm in the region of the sperm tail, referred to as the middle piece. Taken collectively, these data indicate that the authentic RHL-1 and RHL-2/3 genes of the ASGP-R are expressed in late-stage spermatids; however, the Te/Ep RHL- 1-related protein differs in size from the hepatic RHL-1 polypeptide, possibly indicating a specific function of the RHL-1-related protein i n spermatogenesis.