Functional gap junctions are not required for muscle gene activation by induction in Xenopus embryos

Muscle gene expression is known to be induced in animal pole cells of a Xenopus blastula after 2-3 h of close contact with vegetal pole cells. We tested whether this induction requires functional gap junctions between vegetal and animal portions of an animal-vegetal conjugate. Muscle gene transcription was assayed with a muscle-specific actin gene probe and the presence or absence of communication through gap junctions was determined electrophysiologically. Antibodies to gap junction protein were shown to block gap junction communication for the whole of the induction time, but did not prevent successful induction of muscle gene activation. The outcome was the same whether communication between inducing vegetal cells and responding animal cells was blocked by introducing antibodies into vegetal cells alone or into animal cells alone. We conclude that gap junctions are not required for this example of embryonic induction.