Conserved binding recognition elements of sperm chromatin, sperm lipophilic structures and nuclear envelope precursor vesicles

Abstract

Detergent-resistant, lipophilic structures (LSs) at the apex and base of the conical sea urchin sperm nucleus are targets for cytoplasmic membrane vesicle (MV) binding and fuse with these vesicles to form a nuclear envelope in vitro. We report similar LSs associated with trout, frog and mammalian (mouse and bovine) sperm nuclei. The LSs are located at the implantation fossae of all species examined, as well as in the ventral hook region of mouse sperm nuclei. LSs can be removed from, and reconstituted back to, their original sites on nuclei. LS removal prevents MV binding, and reconstitution restores MV binding and GTP-induced fusion activities. Binding of LSs to chromatin or to MVs is mediated, at least in part, by proteins on each structure. Inter-specific LS-chromatin reconstitutions using sea urchin, fish, frog, and mammalian LSs indicate that site-specific binding is not dependent on species. All LSs also bind to MVs of sea urchin or bovine origin, but sea urchin MVs will only fuse with sea urchin LSs, and mammalian MVs only with mammalian LSs. These results demonstrate the conservation between echinoderms, fish, amphibians, and mammals of recognition elements for LS-chromatin and LS-MV binding. The mechanism for fusion of LSs with cytoplasmic MVs, however, is apparently not conserved, and close apposition of MVs on the chromatin surface mediated by LSs is not sufficient to permit MV-MV fusion in the presence of GTP.