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Martens GJ
,
Weterings KA
,
van Zoest ID
,
Jenks BG
.
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In the pars intermedia of the pituitary gland of the amphibian Xenopus laevis the level of mRNA encoding proopiomelanocortin (POMC), the precursor protein for alpha-melanophore-stimulating hormone (alpha-MSH), is shown to be dependent on physiological parameters. POMC mRNA levels in the pars intermedia of black-background-adapted Xenopus are much higher than those of white-adapted animals. These physiological changes in POMC mRNA levels are tissue-specific because they were not found in the pars distalis of the pituitary gland. Background transfer experiments revealed that modulation of POMC gene activity is much slower than changes in the secretion of alpha-MSH.
Fiqure 1. Brarn/pltultary of a fully3e lack-adapted Xenopus after in
situ cDNA:mRNA hybridization using a [ Sl-labelled Xenopus POMC CD=
probe. Tissue sections were 5 micron and exposure time was 3 weeks.
Magnification for A: x16 and for B: x240. C.N.S.: central nervous
system; p.g.: pituitary gland; m.e.: median eminence; p.n.: pars
nervosa; p.i.: pars intermedia; p.d.: pars distalis.
Fiqure 2. Northern blot analysis of POMC mRNA in the pars intermedia
(p.i.) and pars distalis (p-d.) of fully black(B)- and fully white(W)-
adapted Xenopus. In each lane RNA from an extract equivalent to half a
lobe was used. Exposure time was 48 h.
Fiqure 3. Time course of changes in POMC mRNA levels in the Pars
intermedia of Xenopus laevis and of changes in dispersion of pigment
in dermal melanophores (melanophore index) during background adaptation
of the animal. POMC mRNA levels were determined by Northern blot
analysis and scanning of the autoradiograms. The values for the levels
of POMC mRNA (expressed as means + SEMI are the averages of four (a,
B-+W] or three (b, WdB) separate experiments. Asterisks denote those
values that are significantly different (*:p<O.O5 ; **:p<O.OOl) from
that of the controls (i.e. values at time 0). Melanophore index (m.i.)
was determined according to reference 16 with m.i.=5, full dispersion
and m.i.=l, complete aggregation.
