A comparative study of putative melanogenic and melanogenesis inhibiting substances in the vertebrate integument.
It has been suggested that vertebrate pigment patterns are determined and maintained by factors which are present in the integument. The research reported in this dissertation provides some evidence in favor of this supposition. Examination of the deer mouse, Peromyscus boylei, demonstrated that its pale ventral coat integument appears to contain a melanization inhibiting factor (MIF) , and that its dark dorsal coat integument has variable melanization inhibiting factor activity. Additionally, factors present in the dorsal integument appear to permit a greater level of melanization, in vitro, than do those in the ventral integument. The factors, therefore, may be responsible for the dorsal/ventral pigment pattern of this species. Analysis of the Long/Evans hooded rat revealed that its dark coat integument appears to contain a factor which promotes activity of tyrosinase in cultured melanoma cells. This promotion of enzyme activity is greater than, as well as additive to, that produced by the addition of a maximally stimulating dose of α-melanocyte stimulating hormone to melanoma cell cultures. This stimulatory activity is absent in the regions of pale coat integument. Again, such a factor, by its presence or absence, may be responsible for the coat pattern observed in this species. Investigation of an amphibian MIF demonstrated that it appears to have melanization inhibiting activity in mammalian melanoma cells. The amphibian MIF is able to reduce the activity of tyrosinase in cultured mammalian melanoma cells. The inhibitory activity was evident in both the presence and absence of α-MSH. That the amphibian MIF has activity in mammalian cells suggests that pigment pattern regulatory factors may be similar between species and classes of animals. Examination of the channel catfish, Ictalurus punctatus, revealed that its darkly pigmented dorsal integument contains a melanization stimulating factor (MSF). Partial purification of this factor has demonstrated that it is a large molecule (>200 kD) and that it is a protein. Its size and character implicate the catfish MSF as a potential member of the extracellular matrix which could be responsible, at least partially, for the discrete and well-defined dorsal/ventral pigment pattern of this species.
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