DENDRITIC LOCALIZATION OF RAT VASOPRESSIN MESSENGER-RNA - ULTRASTRUCTURAL ANALYSIS AND MAPPING OF TARGETING ELEMENTS

Transcripts encoding the vasopressin precursor are located in axons an d dendrites of rat hypothalamic magnocellular neurons. While the axona l vasopressin mRNA has been extensively characterized both at the bioc hemical and morphological level, little is known about those transcrip ts residing in dendrites of magnocellular neurons. As revealed by in s itu hybridization at the electron microscopic level, the mRNA is locat ed in proximal and distal dendritic segments and is exclusively confin ed to regions containing rough endoplasmic reticulum. These results su ggest that dendrites of hypothalamic neurons may be capable of local p recursor synthesis independent of that occurring in the cell somata. A heterologous system has been employed to define cis-acting elements w ithin the vasopressin mRNA which may be involved in dendritic compartm entalization. Expression vector constructs consisting of the cytomegal ovirus promoter coupled to the rat vasopressin cDNA have been injected into the cell nuclei of cultured neurons derived from embryonic rat s uperior cervical ganglia. Vector-encoded vasopressin transcripts were also sorted to dendrites of these neurons indicating that the molecula r determinants of dendritic mRNA transport are not cell specific. Mapp ing of the targeting elements revealed two segments within the vasopre ssin mRNA that are able to confer dendritic compartmentalization to al pha-tubulin mRNA which is normally confined to the cell body.