Dynamics of proopiomelanocortin and prohormone convertase 2 gene expression in Xenopus melanotrope cells during long-term background adaptation.
The toad Xenopus laevis is able to adapt its skin color to background light intensity. In this neuroendocrine reflex, the proopiomelanocortin (POMC)-derived peptide alpha-melanophore-stimulating hormone (alphaMSH) is a key regulatory factor. In animals adapting to a black background, release of alphaMSH from the pituitary pars intermedia causes dispersal of melanin in skin melanophores. To investigate the long-term in vivo dynamics of alphaMSH production during black background adaptation, the biosynthetic rate of POMC and the contents of POMC, alphaMSH and the POMC processing enzyme precursor convertase 2 (PC2) have been studied in the pars intermedia using pulse-labeling, Western blot and radioimmunoassay. In control animals, adapted to a white background, the rate of POMC biosynthesis and the POMC content were low, while high alphaMSH and PC2 contents were found. After 1 week of adaptation to a black background, the rate of POMC biosynthesis and the POMC protein content had increased 19- and 3.7-fold respectively. These parameters attained a maximum level (28- and 5. 8-fold higher than control) after 3 weeks and remained at these elevated levels for at least 12 weeks. After 1 week, the pars intermedia content of alphaMSH was only 30% of the control level, but after 6 and 12 weeks, the alphaMSH level had increased to the control level. The PC2 content decreased to 52% of control after 1 week and stabilized after 3 weeks at a level slightly lower than the control value. The results show that during long-term background adaptation a steady-state situation is reached, with a balance between the biosynthesis, enzymatic processing and release of alphaMSH. The in vivo dynamics of the processing enzyme PC2 suggest a parallel storage and release of alphaMSH and mature PC2 in the Xenopus pituitary pars intermedia.
Dotman
C H
CH
Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences and Institute for Cellular Signalling, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
van Herp
F
F
Martens
G J
GJ
Jenks
B G
BG
Roubos
E W
EW
D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D015870:Gene Expression; D008297:Male; D010902:Pituitary Gland / Q000737:chemistry / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D045706:Proprotein Convertase 2; D011863:Radioimmunoassay; D013381:Subtilisins / Q000032:analysis* / Q000235:genetics; D014982:Xenopus laevis / Q000378:metabolism*; D000521:alpha-MSH / Q000032:analysis*
D000521:alpha-MSH; D011333:Pro-Opiomelanocortin; D013381:Subtilisins; D045706:Proprotein Convertase 2