Functional Gap Junctions in the Early Sea Urchin Embryo Are Localized to the Vegetal Pole

Abstract

Using the whole-cell voltage-clamp technique we have studied electrical coupling and dye coupling between pairs of blastomeres in 16- to 128-cell-stage sea urchin embryos. Electrical coupling was established between macromeres and micromeres at the 16-cell stage with a junctional conductance (G(j)) of 26 nS that decreased to 12 nS before the next cleavage division. G(j) between descendants of macromeres and micromeres was 12 nS falling to 8 nS in the latter half of the cell cycle. Intercellular current intensity was independent of transjunctional voltage, nondirectional, and sensitive to 1-octanol and therefore appears to be gated through gap junction channels. There was no significant coupling between other pairs of blastomeres. Lucifer yellow did not spread between these electrically coupled cell pairs and in fact significant dye coupling between nonsister cells was observed only at the 128-cell stage. Since 1-octanol inhibited electrical communication between blastomeres at the 16- to 64-cell stage and also induced defects in formation of the archenteron, it is possible that gap junctions play a role in embryonic induction.

Pannexins and gap junction protein diversity

“…This implies either that some multicellular animals have no GJs, or that an additional family(s) of GJ proteins does exist! Physiological data support the postulate regarding a ubiquitous presence of the GJs in Metazoa, including those species that lack identified GJ protein genes [82,83]. Subsequently, we predict the discovery of additional protein families recruited for GJ function in different organisms, potentially even in vertebrates.…”

What is hidden in the pannexin treasure trove: the sneak peek and the guesswork

“…This opens intriguing possibility that genomes of some multicellular organisms do not contain any genes encoding members of known GJ protein families. At the same time physiological data supporting the existence of GJs are convincing for sea urchin [19] and Anthozoa [20]; such that the postulate regarding ubiquity of the GJs in Metazoa should hold true. Although, we ourselves named pannexins, considering them as universal metazoan GJ protein as opposed to Chordate-specific connexins, now it is necessary to admit the fact that we are facing a possibility of the discovery of additional protein families utilized for GJ function.…”

Mechanisms of the epithelial-to-mesenchymal transition in sea urchin embryos

“…52 The wholecell voltage-clamp technique was applied to the 16-to 128-cell stage embryos and detected an intercellular current that is sensitive to 1-octanol, a gap junction inhibitor. 53 Gap junctions provide access between adjacent cells by sharing ions, second messengers and small metabolites through connexins, intercellular channels that are regulated by tyrosine kinases. 54,55 In the plutei of H. pulcherrimus, larval swimming activity is supported in part by the serotonergic nervous system through serotonin secretion into the blastocoel and by signal transmission to the ciliated epithelium through the blastocoelar serotonin receptor cell network.…”