Scholars@Duke

Research in my laboratory is aimed at understanding the molecular basis of gamete interaction leading to fertilization. Our current work is focussed on a key regulatory event of this process: triggered exocytotic release of the sperm's acrosomal vesicle to enable penetration of the egg-specific extracellular matrix, the zona pellucida (zp). Initial sperm interaction with the zp is mediated by ZP3; we have identified a receptor tyrosine kinase, located at the sperm plasma membrane, that serves as a ZP3-receptor. Activation of this receptor, which we have termed zona receptor kinase (ZRK), by liganding ZP3 stimulates its intrinsic tyrosine kinase activity and sets into motion the cascade(s) responsible for acrosomal exocytosis. We have cloned and sequenced human ZRK and found it to be a novel sperm-specific receptor tyrosine kinase. The ZRK extracellular domain of the receptor appears unique and, using synthetic peptides, we have identified epitopes for ZP3 binding. Key to the success of this approach for analysis of human gamete interaction is the availability of the corresponding ligand, human ZP3; toward this end we have constructed an efficient expression system for the production of the human ZPproteins, ZP1, ZP2, and ZP3 in eukaryotic cells. In addition, the intracellular domain of ZRK provides significant sstructural information to permit a productive analysis of downstream activation of signalling cascades involved in regulated exocytosis, which we are pursuing by transfection of mutated kinases in he mammalian testis during early development has revealed an important site of regulated signalling between somatic cells and developing gametes and comprises a research area that we are eager to expand.