Intercellular channels in teleosts: functional characterization of two connexins from Atlantic croaker

Gap junction channels, composed of protein subunits termed connexins, are believed to play a critical role in the process of oocyte differentiation and maturation. We have used the paired Xenopus oocyte assay to characterize functionally two connexin genes, connexin-32.2 and connexin-32.7, recently cloned from the ovary of the Atlantic croaker (Micropogonia undulatus), a species that has emerged as a useful model to study the process of maturation of the ovarian follicle. We have found that, while both connexin proteins were expressed at comparable levels in Xenopus oocytes, only one, connexin-32.2, was functionally competent to induce the formation of intercellular channels. Connexin-32.2 channels exhibited voltage-dependent closure that was similar to, but distinct from that of previously characterized mammalian connexins. In addition, the silent connexin-32.7 was unable to functionally interact with connexin-32.2, either in heterotypic channels or as dominant negative inhibitor. Because connexin-32.2 expression is strikingly regulated during oocyte maturation, these data provide further evidence for a role of intercellular channels in the control of oocyte-follicular cell interactions.