Variability of sperm nuclear basic proteins in the three-spined stickleback and related species of Gasterosteoidei

Abstract

In the present study we have examined the sperm nuclear basic proteins (SNBPs) from mature testes of the three-spined stickleback Gasterosteus aculeatus and three related teleosts in the suborder Gasterosteoidei. Acid/urea polyacrylamide gel electrophoresis (PAGE) of SNBPs from Gasterosteus wheatlandi and Pungitius pungitius (family Gasterosteidae), as well as Aulorhynchus flavidus (family Aulorhynchidae), shows the largest variability of SNBPS in any suborder of teleosts thus far examined. Amino acid analysis reveals a new type of protamine-like SNBP with a high level of arginine (37 mol% in G. aculeatus) along with the presence of histidine and lysine, in agreement with cytochemical results. A PAGE developmental profile shows that the SNBP from freshwater G. aculeatus may undergo post-translational modification during spermiogenesis or, alternatively, may be produced from a higher molecular weight precursor. SNBP variability within the G. aculeatus species complex is much more limited. Although small differences exist between SNBPs from anadromous and freshwater G. aculeatus in lysine/arginine ratios and in the number of multiple electrophoretic bands, small or no differences are detected among SNBPs from different geographically distinct freshwater populations. An exception is in sticklebacks from Paxton Lake and Enos Lake, BC, where relatively recent divergent populations of benthic and limnetic populations are found. Here, G. aculeatus benthic populations show higher levels of residual somatic histones in testes along with the SNBPs, suggesting that chromatin condensation in these mature sperm may differ from that in limnetics.