1. Jon del Castillo1
    1. 1Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada L4A IK6
      2Department of Ecology and Evolution, University of Toronto, Toronto, Ontario, Canada
      3Department of Life Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada
    1. Correspondence should be addressed to D A Lovejoy; Email: david.lovejoy{at}


    Corticotrophin-releasing hormone (CRH) is the pivotal neuroendocrine peptide hormone associated with the regulation of the stress response in vertebrates. However, CRH-like peptides are also found in a number of invertebrate species. The origin of this peptide can be traced to a common ancestor of lineages leading to chordates and to arthropods, postulated to occur some 500 million years ago. Evidence indicates the presence of a single CRH-like receptor and a soluble binding protein system that acted to transduce and regulate the actions of the early CRH peptide. In vertebrates, genome duplications led to the divergence of CRH receptors into CRH1 and CRH2 forms in tandem with the development of four paralogous ligand lineages that included CRH; urotensin I/urocortin (Ucn), Ucn2 and Ucn3. In addition, taxon-specific genome duplications led to further local divergences in CRH ligands and receptors. Functionally, the CRH ligand–receptor system evolved initially as a molecular system to integrate early diuresis and nutrient acquisition. As multicellular organisms evolved into more complex forms, this ligand–receptor system became integrated with the organismal stress response to coordinate homoeostatic challenges with internal energy usage. In vertebrates, CRH and the CRH1 receptor became associated with the hypothalamo-pituitary–adrenal/interrenal axis and the initial stress response, whereas the CRH2 receptor was selected to play a greater role in diuresis, nutrient acquisition and the latter aspects of the stress response.

    • Revision received 27 February 2014
    • Accepted 3 April 2014
    • Made available online as an Accepted Preprint 7 April 2014
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