Synthesis of nerve growth factor mRNA and precursor protein in the thyroid and parathyroid glands of the rat.

Nerve growth factor (NGF) mRNAs were detected in the thyroid and parathyroid glands by hybridization to a preproNGF and a NGF-beta cDNA probe. The thyroid NGF transcript was identical in size to that found in the mouse submaxillary gland. Mature NGF-beta was not detected in the thyroid tissue either by immunoprecipitation or by immunohistochemical methods. In contrast, an antiserum directed against the predicted precursor protein sequence immunoprecipitated a protein of Mr 30,000-31,000 in thyroid extracts. A protein of identical molecular weight was also detected by this serum in the mouse submaxillary gland extracts. In vitro translation of hybrid-selected NGF RNAs detected two peptides of Mrs 35,000 and 28,000. These peptides closely correspond to the proposed translation products of the preproNGF mRNA sequence, suggesting that two different initiation codons can be utilized, at least in vitro. The proNGF antiserum also cross-reacted with the in vitro synthesized Mr 35,000 peptide. The antigenic determinant recognized by the precursor-specific antibody was localized to the convoluted granular tubules of the mouse submaxillary gland, known to be the site of synthesis of the NGF-beta. We present evidence for the localization of unprocessed proNGF in the parathyroid gland and in some parafollicular cells of the thyroid.