The influence of extracellular matrix on reversible gap junction formation in vitro

In vivo gap junctions (gj) are common in the subumbrellar plate endoderm of anthomedusa. When isolated and cultivated in artificial sea water the tissue, consisting of one cell type only, forms a spheroid in which all gap junctions disappear. Gap junction (gj) formation can, however, be induced by attachment and consecutive spreading of the endodermal tissue (spheroid) on stretched extracellular matrix (ECM) material isolated from the polyp stage (with Ca2+-Mg2+-free sea water, without EDTA). Formation, and loss of gj is reversible and strictly corresponds with the alteration from the monolayer 'spread' (on stretched ECM) to 'spheroid' arrangement (no ECM) of the endodermal cells. The functional competence of induced gj is ascertained by injection of Lucifer Yellow, and the transfer of the dye is used to map the pattern of communication. The experimental conditions that result in gj formation simulate the in vivo situation of the endoderm. The influence of the ECM on gj formation, and the structural organization of the isolated endodermal tissue in this well defined in vitro system are discussed.