DEVELOPMENTAL EXPRESSION OF G-PROTEINS AND ADENYLYL-CYCLASE IN PERIPHERAL OLFACTORY SYSTEMS - LIGHT-MICROSCOPIC AND FREEZE-SUBSTITUTION ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMISTRY

Light microscopic immunohistochemistry coupled with freeze-substitutio n electron microscopic immunocytochemistry was used to localize alpha- subunits of G-proteins and type III adenylyl cyclase in developing rat olfactory epithelia. Some cilia immunoreacted with antibodies to G(5 alpha) and type III adenylyl cyclase as early as prenatal day 15 (E15; E1 = sperm-positive), but immunolabelling with antibodies to G(olf al pha) was not observed until E16. From then on numbers of receptor cell s with immunolabelled cilia increased for all three probes. Immunoreac tivity for antibodies to the olfactory signal-transduction proteins te nded to parallel cilium development, though G(olf alpha) lags somewhat behind. Newly formed cilia labelled along their lengths, whereas matu re cilia labelled predominantly along their long distal parts. Dendrit ic knobs and ciliary necklaces showed little or no labelling. While at E22 most multiciliate cells immunolabelled with antibodies to G(5 alp ha), G(olf alpha), and type III adenylyl cyclase, not all of these cel ls labelled with antibodies to olfactory marker protein. Olfactory axo ns immunoreacted more intensely than epithelial surface structures wit h antibodies to G(5 alpha) at E15; the reverse occurred by about E18. Immunoreactivity with antibodies to alpha-subunits of the G-proteins G (o), G(q)/G(11), and G(i) was also found as early as E15. Antibodies t o G(o alpha) labelled receptor cell dendritic knobs and cilia during d evelopment only. Antibodies to G(i alpha) labelled Bowman's glands, wh ereas those to G(q alpha)/G(11 alpha) bound to receptor cell cilia and axons (primarily vomeronasal), and supporting cell microvilli. We pro pose that G(s) is the predominant G protein in cilia of immature olfac tory receptor cells, while G(olf) is predominant in cilia of mature ce lls. Axonal immunoreactivity for some G-protein antibodies suggests G- protein participation in processing of olfactory axon and/or axon term inal-bound signals.