Proopiomelanocortin (POMC) mRNA and POMC-derived peptides immunolocalization in the skin of Protopterus annectens, an African lungfish

Melanocortin Receptor 4 (MC4R) Signaling System in Nile Tilapia

The melanocortin receptor 4 (MC4R) signaling system consists of MC4R, MC4R ligands [melanocyte-stimulating hormone (MSH), adrenocorticotropin (ACTH), agouti-related protein (AgRP)], and melanocortin-2 receptor accessory protein 2 (MRAP2), and it has been proposed to play important roles in feeding and growth in vertebrates. However, the expression and functionality of this system have not been fully characterized in teleosts. Here, we cloned tilapia MC4R, MRAP2b, AgRPs (AgRP, AgRP2), and POMCs (POMCa1, POMCb) genes and characterized the interaction of tilapia MC4R with MRAP2b, AgRP, α-MSH, and ACTH in vitro. The results indicate the following. (1) Tilapia MC4R, MRAP2b, AgRPs, and POMCs share high amino acid identity with their mammalian counterparts. (2) Tilapia MRAP2b could interact with MC4R expressed in CHO cells, as demonstrated by Co-IP assay, and thus decrease MC4R constitutive activity and enhance its sensitivity to ACTH_1-40. (3) As in mammals, AgRP can function as an inverse agonist and antagonist of MC4R, either in the presence or absence of MRAP2b. These data, together with the co-expression of MC4R, MRAP2b, AgRPs, and POMCs in tilapia hypothalamus, suggest that as in mammals, ACTH/α-MSH, AgRP, and MRAP2 can interact with MC4R to control energy balance and thus play conserved roles in the feeding and growth of teleosts.

Chronic stress impairs the local immune response during cutaneous repair in gilthead sea bream (Sparus aurata, L.)

Scale removal in fish triggers a damage-repair program to re-establish the lost epidermis and scale and an associated local immune response. In mammals, chronic stress is known to delay wound healing and to modulate the cutaneous stress axis, but this is unstudied in teleost fish the most successful extant vertebrates. The present study was designed to test the hypothesis that chronic stress impairs cutaneous repair in teleost fish as a consequence of suppression of the immune response. The hypothesis was tested by removing the scales and damaging the skin on one side of the body of fish previously exposed for 4 weeks to a chronic crowding stress and then evaluating cutaneous repair for 1 week. Scale removal caused the loss of the epidermis although at 3days it was re-established. At this stage the basement membrane was significantly thicker (p=0.038) and the hypodermis was significantly thinner (p=0.016) in the regenerating skin of stressed fish relative to the control fish. At 3days, stressed fish also had a significantly lower plasma osmolality (p=0.015) than control fish indicative of reduced barrier function. Chronic stress caused a significant down-regulation of the glucocorticoid receptor (gr) in skin before damage (time 0, p=0.005) and of star at 3 and 7days (p<0.05) after regeneration relative to control fish. In regenerating skin key transcripts of cutaneous repair, pcna, colivα1 and mmp9, and the inflammatory response, tgfβ1, csf-1r, mpo and crtac2, were down-regulated (p<0.05) by chronic stress. Irrespective of chronic stress and in contrast to intact skin many hyper pigmented masses, putative melanomacrophages, infiltrated the epidermis of regenerating skin. This study reveals that chronic stress suppresses the local immune response to scale removal and impairs the expression of key transcripts of wound healing. Elements of the stress axis were identified and modulated by chronic stress during cutaneous repair in gilthead seabream skin.

Molecular cloning of proopiomelanocortin cDNA and multi-tissue mRNA expression in channel catfish

Channel catfish (Ictalurus punctatus) proopiomelanocortin (POMC) cDNA was cloned to investigate its structure, evolution, and expression in different tissues. POMC is an important gene in the hypothalamus-pituitary-adrenal axis, the main mediator of the stress response. POMC gene was isolated from a pituitary cDNA library and nucleotide sequence was determined. POMC cDNA is composed of 1164 nucleotides with a 639 nucleotide open reading frame encoding a protein of 212 amino acids. Catfish POMC protein contains a signal peptide (SP, Met(1)-Ala(28)), N-terminal peptide (Gln(29)-Glu(101)), adrenocorticotropic hormone (ACTH, Ser(104)-Met(142)), alpha-melanocyte stimulating hormone (alpha-MSH, Ser(104)-Val(116)), corticotropin-like intermediate lobe peptide (CLIP, Arg(121)-Met(142)), beta-lipotropin (beta-LPH, Glu(145)-His(212)), gamma-lipotropin (gamma-LPH, Glu(145)- Ser(177)), beta-MSH (Asp(161)-Ser(177)), and beta-endorphin (beta-EP, Tyr(180)-His(212)). Catfish POMC protein does not contain a gamma-MSH region and most of the joining peptide and part of the gamma-LPH are deleted. Protein sequence alignment showed the highest similarity with the carp (Cyprinus carpio) POMC I (66.5%) and POMC II (67%), while the sea lamprey (Petromyzon marinus) POC (17.9%) and POM (18.8%) were the most divergent. The average similarity was 46.95% among the 44 POMC proteins from 36 different species analyzed. Compared to the POMC mRNA levels in the pituitary, the concentration of the POMC mRNA was 0.0594% in the anterior kidney and 0.0012-0.0045% in all the other tissues except in the skin where the lowest expression (0.0005%) was observed. Overall architecture of channel catfish POMC is highly similar to those from other teleosts.