Freeze-fracture analysis of gap and septate junctions in embryos of a moth.

Gap and septate junctions were examined in embryos of Manduca sexta (tobacco hornworm). The junctions observed were similar in structure to those reported for adult insect tissues. In the epidermis typical pleated septate junctions were found. Associated with the pleated septate junctions were inverted gap junctions which had irregularly arranged particles and pits. In the midgut typical smooth septate junctions were found. Associated with these septate junctions were gap junctions which had regular hexagonal packing pattern. This codistribution of gap and septate junctions types is discussed in light of current theories that the gap junction types are alternative forms of the same structure in different metabolic environments. In addition to these gap and septate junctions a new junction, perhaps a modified septate junction, is described.