Trp2 regulates entry of Ca2(+) into mouse sperm triggered by egg ZP3

In many cells, receptor activation initiates sustained Ca2+ entry which is critical in signal transduction(1). Mammalian transient receptor potential (Trp) proteins, which are homologous to the Drosophila photoreceptor-cell T rp protein, have emerged as candidate subunits of the ion channels that med iate this influx. As a consequence of over-expression, these proteins produ ce cation currents that open either after depletion of internal Ca2+ stoves or through receptor activation(2). However, determining the role of endoge nous Trp proteins in signal transduction is complicated by the absence of s elective antagonists. Here we examine Trp function during sperm-egg interac tion, The sperm acrosome reaction is a Ca2+-dependent secretary event that must be completed before fertilization. in mammals, exocytosis is triggered during gamete contact by ZP3, a glycoprotein constituent of the egg's extr acellular matrix, or zona pellucida (ZP). ZP3 activates trimeric G proteins and phospholipase C and causes a transient Ca2+ influx into sperm through T-type Ca2+ channels(3). These early responses promote a second Ca2+-entry pathway, thereby producing sustained increases in intracellular Ca2+ concen tration ([Ca2+](i)) that drive acrosome reactions(4). Our results show that Trp2 is essential for the activation of sustained Ca2+ influx into sperm b y ZP3.