Intrinsic pigment cell stimulating activity in the skin of the leopard frog, Rana pipiens

Melanization stimulating factor (MSF) and melanization inhibiting factor (MIF) in the integument of fish

The present studies were directed to demonstrate that adult fish skin contains putative factors that affect chromatophore and/or chromatoblast function. This hypothesis is based upon the possibility that hypo and/or hyperpigmented areas of the skin are so pigmented because of the localized expression of intrinsic factors that are either stimulatory or inhibitory to the differentiation of specific pigment cell types. In all the morphological and biochemical experiments carried out, we used culture media conditioned by dorsal (DCM) or ventral (VCM) skin from different species of fish. Both DCM and VCM were capable of stimulating differentiation of melanophores in neural crest explants. While the stimulation of melanization is an activity present in both dorsal and ventral skin, an inhibitory activity is also present in ventral skin at such a concentration that it overrides the stimulatory activity afforded by DCM. With biochemical assays, we demonstrated that the three important sequential enzymatic steps in melanogenesis are all stimulated by the conditioned media in a dose-dependent manner and this results in an increase in the amount of melanin present in cultured cells. The results of our investigations provide strong evidence that there are intrinsic pigment cell regulatory factors in the integument of fish, the inhibitory activity being stronger in the ventrum, and that those factors strongly influence, perhaps even determine, the pigment patterns of fish.

Effects of local tissue environment on the differentiation of neural crest cells in turtle, with special reference to understanding the spatial distribution of pigment cells

The spatial distribution of neural crest-derived pigment cells in turtles differs markedly from those found in chickens and mice. One hypothesis to explain such differences in the spatial distribution of pigment cells is that local tissue factors interact with neural crest cells, thereby determining their differentiation into pigment-synthesizing cells. It is reported here that local tissue factors in the soft-shell turtle (Trionyx sinensis japonicus) play a critical role in the development of melanophores from neural crest cells during embryogenesis. Undifferentiated neural crest cells derived from trunk neural tubes were co-cultured in vitro with homochronous somites, or with heterochronous dermis, lung or liver for 14 days. Melanophore differentiation from neural crest cells was significantly promoted when co-cultured with cells from lung, somites or dermis, but not when co-cultured with liver cells. These results suggest that local tissue factors stimulate the differentiation of pluripotent neural crest derivatives toward pigment cells. It is proposed that specific environmental cues play an important role in the spatial distribution of pigment cells in a variety of vertebrate species.

Insights into pigmentary phenomena provided by grafting and chimera formation in the axolotl

The expression of pigmentation patterns in axolotl pigmentary mutants was observed following three types of experimental manipulations including chimera formation, reciprocal neural crest grafts, of gonadal primordia. Three pigmentary genes were utilized including the wild type (D), white (d), and albino (a). In chimeras between white and albino embryos, melanoblasts from the white half crossed the graft interface to differentiate in albino skin. Neural crest grafts from white embryos to albinos provided melanophores of white origin that were capable of differentiation in albino skin. Grafts of gonadal primordia from albino to white embryos provided albino germ cells that formed unpigmented ovocytes together with dark ovocytes: white ovocytes from the albino grafted ovary, and dark ovocytes from the host ovary. The donor albino white ectoderm included in the graft was able to support the differentiation of melanophores, iridophores, and xanthophores that invaded the graft ectoderm from the neural crest of the white host. It was concluded that manifestation of the white or wild phenotypes may be related to the possible presence or absence of inhibiting or stimulating pigmentary factors in the skin. This possibility was discussed in the light of recent discoveries of such factors as Agouti Signaling Protein (ASP) from mammalian skin.

Melanization stimulating activity in the skin of the gilthead porgy, Sparus auratus

The presence of a melanization-stimulating factor (MSF) was discovered in dorsal and/or ventral skin of Sparus auratus. Skin from this marine species was used to condition Steinberg's balanced salt solution (BSS), which was subsequently tested with the neural tube assay. BBS conditioned by dorsal and/or ventral skin of S. auratus at 25% and 50% concentrations had a profound stimulatory effect on the percentage of melanization of neural crest cells throughout the 3-day assay period. In some cases 90% melanization occurred within the first 24 hr. Such stimulated cells showed a doubling of the number of dendrites per cell. To assess the effects of MSF on other indices of melanization, dorsal and/or ventral skin was used to condition MEM used in the culture of B16-F10 murine melanoma cells. During the first 24 hr, B16-F10 murine melanoma cells responded to conditioned media by demonstrating a considerable increase in activities of tyrosine hydroxylase, dopa oxidase, and dopachrome tautomerase, but no effect was observed on melanin content. In contrast, melanin content increased after 48 hr of incubation, whereas the enzymatic activities were inhibited during this period. It seems that MSF activity, expressed in several ways, may be present generally among marine species.

Observations on the development of unusual melanization of leopard frog ventral skin

The ontogeny of ventral pigmentation of two species of leopard frog, Rana pipiens and R. chiricahuensis, was examined by light microscopy and transmission electron microscopy to reveal how the unusual melanistic ventral pigmentation of R. chiricahuensis is achieved at the cellular level. Ventral skin of R. pipiens is always white. Ventral skin of adult R. chiricahuensis is white when frogs are background-adapted to a white substrate, but ventral skin becomes nearly as dark colored as the dorsal skin when frogs darken in response to a black background. Skin samples from tadpoles of both species, newly metamorphosed frogs, and adult frogs were analyzed for chromatophore composition and distribution. Ventral skin of R. pipiens larvae, newly metamorphosed frogs, and adults and of R. chiricahuensis larvae was white due to abundant iridophores and no melanophores. Melanophore density in the ventral integument of R. chiricahuensis was 9.1 +/- 2.8/mm2 in newly metamorphosed frogs and 87.0 +/- 4.8/mm2 in adult frogs. Pigment within ventral melanophores migrated during physiological color change during background adaptation.