Effects of perturbation of cell polarity on molecular markers of sperm-eggbinding sites on mouse eggs

The mouse germinal vesicle (CV)-intact oocyte is a symmetric cell, with the CV centrally localized and with components of the plasma membrane and cort ex symmetrically distributed around the periphery of the oocyte. During ooc yte maturation, two distinct regions of the egg plasma membrane and cortex develop: the amicrovillar region overlying the meiotic spindle and the micr ovillar region. The development of this polarity is significant, since sper m bind to and fuse with the microvillar region. We are interested in the de velopment of egg polarity and have characterized the localizations of sever al markers for egg polarity in normal metaphase II eggs and CV-intact oocyt es. The asymmetric distributions of these markers including actin, cortical granules, binding sites for the sperm proteins fertilin alpha and fertilin beta, and two different beta(1) integrin epitopes) develop during oocyte m aturation in vitro, and this polarity can be perturbed by treatments that d isrupt the actin microfilaments or microtubules. In addition, immunoelectro n microscopy reveals that binding sites for recombinant fertilin beta are s pecifically localized to the microvillar region, suggesting that the bindin g sites for this sperm ligand are either specifically localized or activate d in this region, these results indicate that structural remodeling of the mouse egg plasma membrane is accompanied by molecular remodeling, resulting in the localization or activation of specific molecules in subdomains of t he plasma membrane.