Intercellular junctions, intramembranous particles and cytoskeletal elements of deep cells of the Fundulus gastrula

The fine structure of motile deep cells of the gastrula stage of Fundulus heteroclitus was studied with transmission electron microscopy, using both thin sectioning and freeze-cleave techniques. Gastrula deep cells form extensive non-junctiona appositions with each other, in which the apposed plasma membranes are parallel and separated by a distance of 26-28 nm. They also form gap junctions. Tight junctions, desmosomes, and extensive interdigitations of apposed plasma membranes were not observed. The plasma membranes of deep cells contain numerous unclustered intramembranous particles. Cytoplasmic microtubules were found, but they appear to be small in number, sparsely distributed, and mainly randomly oriented. Microfilaments are also present and are localized largely in the cortical cytoplasm and in thin cell extensions. The significance of these findings for the contact and locomotory behavior of deep cells is discussed.