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-substitution 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 alpha) was not observed until E16. From then on numbers of receptor cells with immunolabelled cilia increased for all three probes. Immunoreactivity for antibodies to the olfactory signal-transduction proteins tended to parallel cilium development, though G(olf alpha) lags somewhat behind. Newly formed cilia labelled along their lengths, whereas mature cilia labelled predominantly along their long distal parts. Dendritic knobs and ciliary necklaces showed little or no labelling. While at E22 most multiciliate cells immunolabelled with antibodies to G(5 alpha), G(olf alpha), and type III adenylyl cyclase, not all of these cells labelled with antibodies to olfactory marker protein. Olfactory axons immunoreacted more intensely than epithelial surface structures with 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 to G(o alpha) labelled receptor cell dendritic knobs and cilia during development only. Antibodies to G(i alpha) labelled Bowman's glands, whereas those to G(q alpha)/G(11 alpha) bound to receptor cell cilia and axons (primarily vomeronasal), and supporting cell microvilli. We propose that G(s) is the predominant G protein in cilia of immature olfactory receptor cells, while G(olf) is predominant in cilia of mature cells. Axonal immunoreactivity for some G-protein antibodies suggests G-protein participation in processing of olfactory axon and/or axon terminal-bound signals.