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. Mammalian transient receptor potential (Trp) proteins, which are homologous to the Drosophila photoreceptor-cell Trp protein, have emerged as candidate subunits of the ion channels that mediate this influx. As a consequence of overexpression, these proteins produce cation currents that open either after depletion of internal Ca2+ stores or through receptor activation. However, determining the role of endogenous Trp proteins in signal transduction is complicated by the absence of selective antagonists. Here we examine Trp function during sperm-egg interaction. The sperm acrosome reaction is a Ca2+-dependent secretory event that must be completed before fertilization. In mammals, exocytosis is triggered during gamete contact by ZP3, a glycoprotein constituent of the egg's extracellular 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. These early responses promote a second Ca2+-entry pathway, thereby producing sustained increases in intracellular Ca2+ concentration ([Ca2+]i) that drive acrosome reactions. Our results show that Trp2 is essential for the activation of sustained Ca2+ influx into sperm by ZP3.
Jungnickel
M K
MK
Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Marrero
H
H
Birnbaumer
L
L
Lémos
J R
JR
Florman
H M
HM
D020101:Acrosome Reaction; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D005089:Exocytosis; D005306:Fertilization; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D008969:Molecular Sequence Data; D010063:Ovum / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011956:Receptors, Cell Surface; D015398:Signal Transduction; D013094:Spermatozoa / Q000378:metabolism*; D050052:TRPC Cation Channels; D019284:Thapsigargin / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D000072216:Zona Pellucida Glycoproteins
D004527:Egg Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D050052:TRPC Cation Channels; C113139:Trp2 protein, vertebrate; C491858:Trpc2 protein, mouse; D000072216:Zona Pellucida Glycoproteins; C000606521:Zp3 protein, mouse; D019284:Thapsigargin; D010738:Type C Phospholipases; D002118:Calcium