The Pituitary‐Skin Connection in Amphibians: Reciprocal Regulation of Melanotrope Cells and Dermal Melanocytes

Abstract

In amphibians, ␣ -MSH secreted by the pars intermedia of the pituitary plays a pivotal role in the process of skin color adaptation. Reciprocally, the skin of amphibians contains a number of regulatory peptides, some of which have been found to regulate the activity of pituitary melanotrope cells. In particular, the skin of certain species of amphibians harbours considerable amounts of thyrotropin-releasing hormone, a highly potent stimulator of ␣ -MSH release. Recently, we have isolated and sequenced from the skin of the frog Phyllomedusa bicolor -a novel peptide named skin peptide tyrosine tyrosine (SPYY), which exhibits 94% similarity with PYY from the frog Rana ridibunda. For concentrations ranging from 5 ؋ 10 -10 to 10 -7 M, SPYY induces a dose-related inhibition of ␣ -MSH secretion. At a dose of 10 -7 M, SPYY totally abolished ␣ -MSH release. These data strongly suggest the existence of a regulatory loop between the pars intermedia of the pituitary and the skin in amphibians.

Distribution of Thyrotropin-Releasing Hormone (TRH) Immunoreactivity in the Brain of Urodele Amphibians

“…In fact, the sequence of TRH has been fully conserved across the vertebrate phylum, indicating that strong evolutionary pressure has acted to preserve the structure of this peptide [Vaudry et al, 1999]. Therefore, the use of antibodies against mammalian TRH seems a valuable tool for unraveling TRH immunoreactive structures in different vertebrates.…”

Evolutionarily conserved TRH neuropeptide pathway regulates growth in Caenorhabditis elegans

“…In 1969 the groups of Schally and Guillemin isolated the tripeptide pQHP-NH 2 (2,3), named "thyrotropin-releasing hormone" (TRH). The sequence of TRH is fully conserved across all vertebrates, indicating that strong evolutionary pressure has acted to preserve its structure (4). In all vertebrate phyla TRH is synthesized from a larger precursor protein (preproTRH) that contains five to eight copies of the TRH sequence (4).…”

“…The sequence of TRH is fully conserved across all vertebrates, indicating that strong evolutionary pressure has acted to preserve its structure (4). In all vertebrate phyla TRH is synthesized from a larger precursor protein (preproTRH) that contains five to eight copies of the TRH sequence (4). Following the explosion of genome and transcriptome sequence data, preproTRH was identified in chordate species lacking a bona fide pituitary, e.g., cephalochordates (5), and in the genomes of more ancient deuterostomes, including echinoderms (6,7).…”

Plasticity in the Melanotrope Neuroendocrine Interface of <i>Xenopus laevis</i>

“…The fact that the reflex is so easy to turn on and off (simply change the color of background) has aided in studies aimed at elucidating cellular and molecular mechanisms involved in the activation and inactivation of this neuroendocrine transducer cell. Such studies have focused on two amphibian species, Rana ridibunda [2, 3] and Xenopus laevis [4]. Both neuropeptides, such as TRH [5] and NPY [6], as well as small molecule neurotransmitters such as dopamine [7], GABA [8] and adenosine [9] are established regulators of melanotrope cell function in Rana ridibunda .…”