Ontogeny of connexin 32 and 43 expression in the cerebral cortices of ovine fetuses, newborns, and adults.

Gap junctions are specialized membrane structures that mediate intercellular communication and facilitate passage of ions and small molecules between adjacent cells. Connexins comprise a multigene family of transmembrane proteins that form gap junctions. Connexin-32 and connexin-43 are among the most abundant connexins in brain and are highly expressed during development. Connexin-32 is expressed primarily in oligodendrocytes and connexin-43 in astrocytes in adult brain. However, both connexins are expressed in neurons during development. We examined the effects of ontogeny on connexin-32 and connexin-43 protein abundance in cerebral cortices of sheep during development. Western immunoblot was used to measure connexin-32 and connexin-43 expression in cerebral cortices of fetuses at 60%, 80%, and 90% of gestation, in newborn lambs and adult sheep. Values were expressed as ratios to a single adult control cerebral cortical sample. Connexin-32 abundance was higher (P<0.05) in cerebral cortices of fetuses at 60% of gestation (3.0+/-0.68, mean+/-SD), than in those at 90% of gestation (1.7+/-0.3), in newborn (1.8+/-0.55), and adult sheep (0.84+/-0.19), respectively. In contrast, connexin-43 abundance was higher (P<0.05) in cerebral cortices of fetuses at 90% of gestation (0.44+/-0.17), newborn (0.69+/-0.12) and adult sheep (1.14+/-0.13), than in those at 60% of gestation (0.05+/-0.01). We conclude that (1) connexin-32 and connexin-43 protein are expressed early in fetal life and throughout development, (2) each connexin displays a unique pattern of change with development, (3) connexin-43 exhibited ontogenic increases in protein abundance, whereas, connexin-32 exhibited reciprocal decreases in abundance late in fetal development, in newborn and adult sheep.