EXPRESSION OF A HUMAN INSULIN TRANSGENE IN CHOLINERGIC NEURONS OF THEMOUSE MEDIAL HABENULA

We explored the possibility that an insulin gene deleted in its 5'-fla nking region is expressed in adult mouse brain. We used three independ ent lines of mice carrying a human insulin transgene which included th e insulin gene transcription unit flanked by 168 base pairs upstream a nd 5.5 kb downstream. Using a reverse transcription-polymerase chain r eaction assay, human insulin mRNAs were detected in whole brain extrac ts. In all three lines, human insulin mRNAs were localized by in situ hybridization in a single cerebral site, the medial habenula. With a m onoclonal antibody specific for human C-peptide and human proinsulin, labelling was restricted to a subset of habenular cholinergic neurons, with rare immunostained fibers. No labelling was observed in the proj ection fibers of the retroflexus fasciculus or in their axon terminals in the interpeduncular nucleus. Electron microscope studies suggested that the processing of the human peptide involved the endoplasmic ret iculum and Golgi apparatus, but there were no secretory granules in th e transgene expressing cells. These findings demonstrate that the huma n insulin transgene tested here includes a habenula specific promoter which could be useful for physiological and molecular studies on the h abenula.