EXPRESSION OF A DOMINANT-NEGATIVE INHIBITOR OF INTERCELLULAR COMMUNICATION IN THE EARLY XENOPUS EMBRYO CAUSES DELAMINATION AND EXTRUSION OFCELLS

A chimeric construct, termed 3243H7, composed of fused portions of the rat gap junction proteins connexin32 (Cx32) and connexin43 (Cx43) has been shown to have selective dominant inhibitory activity when tested in the Xenopus oocyte pair system. Co-injection of mRNA coding for 32 43H7 together with mRNAs coding for Cx32 or Cx43 completely blocked th e development of channel conductances, while the construct was ineffec tive at blocking intercellular channel assembly when coinjected with r at connexin37 (Cx37). Injection of 3243H7 into the right anterodorsal blastomere of 8-cell-stage Xenopus embryos resulted in disadhesion and delamination of the resultant clone of cells evident by embryonic sta ge 8; a substantial number, although not all, of the progeny of the in jected cell were eliminated from the embryo by stage 12. A second cons truct, 3243H8, differing from 3243H7 in the relative position of the m iddle splice, had no dominant negative activity in the oocyte pair ass ay, nor any detectable effects on Xenopus development, even when injec ted at four-fold higher concentrations. The 3243H7-induced embryonic d efects could be rescued by coinjection of Cx37 with 3243H7. A blastome re reaggregation assay was used to demonstrate that a depression of dy e-transfer could be detected in 3243H7-injected cells as early as stag e 7; Lucifer yellow injections into single cells also demonstrated tha t injection of 3243H7 resulted in a block of intercellular communicati on. These experiments indicate that maintenance of embryonic cell adhe sion with concomitant positional information requires gap junction-med iated intercellular communication.