Abstract
Analysis of RNA from day old rat brain neuronal cell cultures and adult salivary gland tissue revealed a 2.4Kb polyA+ RNA species that hybridized to both cloned human and rat insulin genomic probes. Hybridization was not observed between glial cell RNA and either insulin DNA probe. The abundance of the 2.4Kb RNA species was 83 copies/neuronal cell and 14.5 copies/cell in the submandibular gland. Mature preproinsulin mRNA (PPImRNA) was not detected in either tissue. The 2.4Kb RNA was present in the adult pancreas at very low levels (<10 copies/cell vs. 1600 copies/cell for the PPImRNA). Immunofluorescent studies with purified anti-insulin antibodies detected a sub-population of neuronal cells (5%) and scattered ductal epithelium in the submandibular gland as sources of extrapancreatic insulin synthesis.
Others have postulated the extrapancreatic synthesis of insulin based on the presence of low but detectable levels of protein in various tissues. Most controversial has been the discussion centered on the brain as a site of insulin synthesis. Our results suggest that two distinct tissues, the brain and the submandibular gland, possess unique cell types that contain both (i) a 2.4Kb RNA species that hybridizes with an insulin gene and (ii) positive anti-insulin immunofluorescence staining patterns. This may indicate that the insulin gene(s) is expressed in brain and salivary gland and that both tissues are potential de novo synthetic sites.
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Cooper, D., Clarke, D. & Rosenbloom, A. 1202 TRANSCRIPTION OF THE INSULIN GENE IN THE BRAIN AND SUBMANDIBULAR GLAND OF THE RAT. Pediatr Res 19, 311 (1985). https://doi.org/10.1203/00006450-198504000-01232
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DOI: https://doi.org/10.1203/00006450-198504000-01232
