The zona pellucida is an extracellular matrix that is composed of three glycoproteins, which is a major secretory product of growing oocytes and can also be found on ovulated eggs and early embryos. The fertilized ovum is surrounded by this matrix of mucoproteins, which separates the egg from a layer of follicle cells that provide nourishment to the egg.
Three components of the mouse zona pellucida have been identified (ZP1, ZP2, and ZP3) and contain a signal sequence that directs the protein into a secretory pathway and is cleaved from the mature protein, and a transmembrane domain. In mice these three genes are expressed in a coordinate, oocyte-specific manner during the growth of oogenesis. See, for example, Epifano, O. et al., Development 121: 1947-1956, 1995.
In the mouse model of fertilization, the ZP3 protein first binds the sperm, followed by the binding of ZP2. ZP1 then crosslinks ZP3 and ZP2 dimers. The interaction of these three proteins with the sperm result in the induction of the acrosome reaction (Bork, P. et al., FEBS 300:237-240, 1992). Thus the zona pellucida plays a critical role in fertilization and the post-fertilization block to polyspermy.
Thus genes of the zona pellucida (ZP) family and their encoded proteins are critical in understanding the process of fertilization. The identification of additional members of this family is needed to study this process and to develop methods to modulate it. The present invention provides a novel member of the zona pellucida proteins and related compositions whose uses will be apparent to those skilled in the art from the teachings herein.