TELOMERE-TELOMERE INTERACTIONS AND CANDIDATE TELOMERE BINDING PROTEIN(S) IN MAMMALIAN SPERM CELLS

We have used fluorescent in situ hybridization to localize telomeres w ithin the nuclei of sperm from six mammals (human, rat, mouse, stallio n, boar, and bull). In minimally swollen sperm of mouse and rat, most of the telomeres are clustered within a limited area in the posterior part of nuclei. In sperm of other species, telomeres associate into te trameres and dimers. On swelling of sperm cells with heparin/dithiotri ethol, telomere associations disperse, and hybridization signals becom e smaller in size and their numbers approach or correspond to the numb er of chromosome ends in a haploid genome. Quantitation of telomere lo ci indicates that dimeric associations are prominent features of mamma lian sperm nuclear architecture. Higher order telomere-telomere intera ctions and organization develop during-meiotic stages of human spermat ogenesis. At this stage, telomeres also become associated with the nuc lear membrane. In an attempt to elucidate the molecular mechanisms und erlying telomere interactions in sperm, we have identified a novel pro tein activity that binds to the double-stranded telomeric repeat (TTAG GG)(n). Sperm telomere binding protein(s) (STEP) was extracted from hu man and bull sperm by 0.5 M NaCl. STEP does not bind single-stranded t elomeric DNA and is highly specific for single base substitutions in a duplex DNA sequence. Depending on the conditions of binding, we obser ved the formation of several nucleoprotein complexes. We have shown th at there is a transition between complexes, which indicates that the s lower migrating complex is a multimer of the higher mobility one. We p ropose that STEP participates in association between the telomere doma ins which were microscopically observed in mammalian spermatozoa. (C) 1997 Academic Press.