Ontogeny of thyrotropin-releasing hormone biosynthesis and release in hypothalamic neurons

Thyrotropin-releasing hormone (TRH) is expressed at early postmitotic stages of hypothalamic neuron development, in the mouse and rat, as revealed by the presence of the mature peptide, of pro-TRH mRNAs, and of large precursor forms. This indicates a coordinate expression of several genes encoding, respectively, pro-TRH, its processing enzymes, and the cell machinery for intracellular transport, sorting, and release of TRH. During development, an acceleration of pro-TRH processing is revealed by an increased proportion of the mature peptide. This is correlated with changes in the respective distribution of pro-TRH and TRH along neurites and the ontogenesis of neurosecretory granules.