EXPRESSION AND IMMUNOLOCALIZATION OF P59(C-FYN) TYROSINE KINASE IN RAT EGGS

Fertilization overcomes meiotic arrest by triggering a series of bioch emical events, resulting in activation of the egg. A small group of pr otein tyrosine kinases (PTKs) have been identified in eggs of inverteb rates and lower vertebrates and inhibitor studies have suggested that they play a role in late events of egg activation. A recent study usin g the sea urchin system demonstrated that Fyn kinase was expressed in eggs and was activated within minutes of fertilization. In the present study, Western blot analysis as well as immune complex kinase assay d emonstrated that p59(c-fyn) kinase was expressed in both unfertilized and fertilized rat eggs. Immunofluorescence confocal microscopy demons trated that Fyn kinase was localized to the egg cortex but also to the polar body and the fertilizing cone which are elevated from the corti cal cytoplasm of the activated egg. Surprisingly, Fyn was also found t o be highly concentrated over the meiotic and mitotic spindles. To dat e, Fyn is the first PTK demonstrated to be present in the mammalian eg g. Localization of Fyn to the egg cortex as well as the spindle microt ubules indicates that this protein kinase may have multiple functions within the egg. (C) 1998 Academic Press.