Connexins in the developing salivary glands.

Freeze-fracture and immunohistochemistry were used to elucidate the ultrastructure of gap junctions and the expression of connexins (gap junction structural proteins) Cx32 and Cx43 in the developing rat submandibular glands. Developing rat submandibular glands were examined from the 17th gestational day to the 14th day after birth. Gap junctions could be observed as clusters of particles 9-12 nm in diameter during the gestational days. The junctions were very small and consisted of about 20 particles in a relatively regular arrangement with a wide center-to-center spacing of 15-18 nm on the PF face. Fluorescence spots reacting positively to Cx43 were found between glandular cells from the 17th gestational day. Very few spots positive to Cx32 could be detected during gestation, their numbers increasing after birth. The possibility that Cx32 may have a role in the establishment of secretory regulation and that Cx43 is associated before birth with glandular growth and differentiation is discussed.