EXPRESSION OF PREPROTACHYKININ-A AND NEUROPEPTIDE-Y MESSENGER-RNA IN THE THYMUS

The preprotachykinin-A gene, the common gene of mRNAs encoding both substance-P (SP) and neu-rokinin-A (NKA), was shown to be expressed in Sprague-Dawley rat thymus by detection of specific mRNA in gel-blot analyses. In situ hybridization revealed dispersed PPT-A-labeled cells in sections from rat thymus, with a concentration of grains over a subpopulation of cells in the thymic medulla. Also, neuropeptide-Y mRNA-expressing cells were found in the rat thymus, primarily in the thymic medulla. Rat thymic extracts contained SP-like immunoreac-tivity (SP-LI), and the major part of the immunoreac-tivity coeluted with authentic SP and SP sulfoxide standards. SP-LI was also detected in human thymus, which contained between 0.09-0.88 ng SP-LI/ g wet wt. Evidence for translation of preprotachyki-nin-A mRNA in the rat thymus was obtained from the demonstration of NKA-LI in thymic cells with an epithelial-like cell morphology. Combined with previous observations on the immunoregulatory roles of tachykinin peptides and the existence of specific receptors on immunocompetent cells, the demonstration of intrathymic synthesis of NKA suggests a role for NKA-LI peptides in T-cell differentiation in the thymus. © 1990 by The Endocrine Society.