Late-stage spermatids are characterized by expression of the "liver-specific" asialoglycoprotein receptor, RHL-1.

The major and minor forms of the asialoglycoprotein receptor (ASGP-R), designated in the rat as RHL-1 and RHL-2/3, respectively, have traditionally been considered to be expressed exclusively in hepatic parenchymal cells. Northern blot analysis now demonstrates that rat and mouse testis express a receptor similar to the RHL-1 ASGP-R but not the RHL-2/3 receptor. In situ hybridization studies demonstrate that late-stage mouse and rat spermatids are the testicular cells that express the RHL-1 ASGP-R. The rat spermatid RHL-1 receptor has functional binding capability, with a KD of approximately 1.4 x 10(-8) M, and similar characteristics, compared with the hepatic RHL-1 receptor, regarding ligand binding specificity and ion dependence. These findings have major implications for therapeutic procedures attempting to target cytotoxic agents or DNA to hepatocytes using the ASGP-R. In addition, these findings demonstrate that late-stage spermatids are transcriptionally active and suggest that the RHL-1 receptor may have a functional role in sperm maturation and/or fertilization.