Intercellular junctions in the Xenopus embryo prior to gastrulation.

A freeze-fracture study of Xenopus embryos at the eight-cell stage revealed the presence of tight junctions and small aggregations of 120 A diameter intramembranous particles. These aggregations consisted of up to ten particles and resembled forming gap junctions. Examination of early blastulae showed that fully developed gap junctions were present, apparently occurring very infrequently. These results support the contention that specialized junctions mediate electrical coupling during early amphibian development.