Expression of multiple Src family kinases in sea urchin eggs and their function in Ca release at fertilization

Egg activation at fertilization in deuterostomes requires a rise in intracellular Ca2+, which is released from the egg's endoplasmic reticulum. In sea urchins, a Src Family Kinase (SpSFK1) is necessary for the PLCg-mediated signaling event that initiates this Ca2+ release (Giusti, A.F., O'Neill, F.J., Yamasu, K., Foltz, K.R. and Jaffe, L.A., 2003. Function of a sea urchin egg Src family kinase in initiating Ca2+ release at fertilization. Dev. Biol. 256, 367-378.). Annotation of the Strongylocentrotus purpuratus genome sequence led to the identification of additional, predicted SFKs (Bradham, C.A., Foltz, D.R., Beane, W.S., Amone, M.I., Rizzo, F., Coffman, J.A., Mushegian, A., Goel, M., Morales, J., Geneviere, A.M., Lapraz, F., Robertson, A.J., Kelkar, H., Loza-Coll, M., Townley, I.K., Raisch, M., Roux, M.M., Lepage, T., Gache, C., McClay, D.R., Manning, G., 2006. The sea urchin kinome: a first look. Dev. Biol. 300, 180-193.; Roux, M.M., Townley, I.K., Raisch, M., Reade, A., Bradham, C., Humphreys, G., Gunaratne, H.J., Killian, C.E., Moy, G., Su, Y.H., Ettensohn, C.A., Wilt, F., Vacquier, V.D., Burke, R.D., Wessel, G. and Foltz, K.R., 2006. A functional genomic and proteomic perspective of sea urchin calcium signaling and egg activation. Dev. Biol. 300, 416-433.). Here, we describe the cloning and characterization of these 4 additional SFKs and test their function during the initial Ca2+ release at fertilization using the dominant-interfering microinjection method coupled with Ca2+ recording. While two of the new SFKs (SpFrk and SpSFK3) are necessary for Ca2+ release, SpSFK5 appears dispensable for early egg to embryo transition events. Interestingly, SpSFK7 may be involved in preventing precocious release of Ca2+. Binding studies indicate that only SpSFK1 is capable of direct interaction with PLCg. Immunolocalization studies suggest that one or more SpSFK and PLCg are localized to the egg cortex and at the site of sperm-egg interaction. Collectively, these data indicate that more than one SFK is involved in the Ca2+ release pathway at fertilization.