Ion measurements in sea urchin sperm

Monoclonal antibodies to a membrane glycoprotein induce the phosphorylation of histone H1 in sea urchin spermatozoa

Two groups of mAbs reacting with external domains of a major sea urchin sperm membrane glycoprotein of 210 kD were isolated. Previous studies have shown that group I mAbs inhibit the acrosome reaction induced by egg jelly and also cause large increases in intracellular Ca2+ [( Ca2+]i). Group II mAbs, at comparable levels of cell surface binding, neither inhibit the egg jelly-induced acrosome reaction nor cause increases in [Ca2+]i. In this paper, we investigate the ability of these mAbs to induce the cAMP-dependent phosphorylation of sperm histone H1. Group I mAbs induce H1 phosphorylation to the same level and on the same peptide, as occurs upon treatment of sperm with egg jelly. These mAbs also activate adenylate cyclase to the same extent as egg jelly. Group II mAbs do not induce H1 phosphorylation and are only poor activators of adenylate cyclase. Group I mAbs compete with each other, but not with group II mAbs, for binding to the cell surface. These data indicate that the activation of adenylate cyclase is an initial event in the pathway leading from the binding of mAbs to a specific domain of the 210-kD protein at the cell surface, to the discrete phosphorylation of histone H1 in highly condensed sperm chromatin. The domain on the 210-kD protein recognized by group I mAbs plays a critical role in signal transduction during the early events of fertilization.

Monoclonal antibodies increase intracellular Ca2+ in sea urchin spermatozoa

Changes in intracellular free Ca2+ ([Ca2+]i) of sea urchin (Strongylocentrotus purpuratus) spermatozoa were measured using the fluorescent Ca2+ indicators fura-2 and indo-1. The intracellular pH (pHi) of sperm was also determined. The fucose sulfate-rich glycoconjugate component of egg jelly induced increases in [Ca2+]i and pHi in sperm and induced the acrosome reaction. Monoclonal antibodies (mAbs) to external domains of a 210-kDa glycoprotein of the sperm plasma membrane induced a 23-fold increase in [Ca2+]i (vs. 9-fold for fucose sulfate-rich glycoconjugate), but the mAbs did not cause the pHi to increase and did not induce the acrosome reaction. When the mAb treatment which induced an increase in [Ca2+]i was combined with an NH4Cl treatment, which increased the pHi, the acrosome reaction was induced. mAb-induced increases in [Ca2+]i were dependent on millimolar concentrations of extracellular Ca2+ and were reversed by placing sperm in Ca2+-free seawater or by chelating Ca2+ with EGTA. The mAb-induced [Ca2+]i increase was sensitive to the pH of the seawater, although mAb binding was not. The data show that increased [Ca2+]i and pHi are necessary for induction of the acrosome reaction and suggest that the 210-kDa protein may play a role in regulating Ca2+ entry into the spermatozoan. These mAbs make it possible to separate the increase in [Ca2+]i from the increase in pHi and may be useful in the elucidation of the regulatory role of Ca2+ in sperm physiology.