Sci. STKE, 28 January 2003
Fertilization Starting Out with a New Second Messenger
Churchill et al. put the final piece into place to designate nicotinic acid adenine dinucleotide phosphate (NAADP) as a second messenger. Although the Ca2+-mobilizing agent NAADP fulfills many criteria for a second messenger, its concentration inside cells has never been shown to increase after a physiologically relevant stimulus. Churchill et al. investigated the role of NAADP in sea urchin egg fertilization. The authors used a radioreceptor assay to demonstrate a biphasic increase in NAADP in extracts of eggs and sperm after fertilization. An increase in NAADP similar in magnitude to the earlier peak occurred in sperm incubated with egg jelly, indicating that this increase was due to NAADP production in sperm. Fertilization depleted NAADP-sensitive Ca2+ stores in egg homogenates, but not Ca2+ stores mobilized by inositol-1,4,5-trisphosphate (IP3) or cyclic adenosine diphosphate ribose (cADPR). Intra-oocyte photorelease of NAADP--but not IP3, Ca2+, or cADPR--elicited an increase in Ca2+ throughout the egg cortex (a cortical flash) that depended on Ca2+ influx, as is seen after fertilization. Repeated release of NAADP led to desensitization of the NAADP-triggered cortical flash and also inhibited the cortical flash to fertilization. These data suggest that exposure to the egg elicits NAADP production by the sperm, which then introduces the NAADP into the egg, triggering the cortical flash. The increase in NAADP after fertilization, combined with the similarity in the response of the egg to NAADP to the sequelae of fertilization, establish NAADP as a bona fide second messenger in the sea urchin oocyte.
G. C. Churchill, J. S. O'Neill, R. Masgrau, S. Patel, J. M. Thomas, A. A. Genazzani, A. Galione, Sperm deliver a new second messenger: NAADP. Curr. Biol. 13, 125-128 (2003). [Online Journal]
Citation: Starting Out with a New Second Messenger. Sci. STKE 2003, tw40 (2003).
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