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 inclu ding chimera formation, reciprocal neural crest grafts, and grafts of gonadal primordia. Three pigmentary genes were utilized including the wild type (D), white (d), and albino (a). In chimeras between white an d albino embryos, melanoblasts from the white half crossed the graft i nterface to differentiate in albino skin. Neural crest grafts from whi te 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 u npigmented ovocytes together with dark ovocytes: white ovocytes from t he albino grafted ovary, and dark ovocytes from the host ovary. The do nor albino white ectoderm included in the graft was able to support th e 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 stimul ating pigmentary factors in the skin. This possibility was discussed i n the light of recent discoveries of such factors as Agouti Signaling Protein (ASP) from mammalian skin.