EVIDENCE THAT MIF PLAYS A ROLE IN THE DEVELOPMENT OF PIGMENTATION PATTERNS IN THE FROG

A ventrally localized melanization-inhibiting factor (MIF) may play an important role in the expression of dorsal-ventral pigment patterns o f amphibians. In efforts to purify this putative MIF, ventral skin con ditioned medium (VCM) from Rana forreri was partially fractionated and used to immunize mice. A monoclonal antibody that has the ability to block the activity of MIP was isolated, and an immunoaffinity matrix w as prepared by cross-linking the antibody to protein G-Sepharose. The fraction of VCM that bound to the affinity matrix decreased the number of melanized cells in the Xenopus laevis neural tube explant assay, b ut did not reduce significantly the number of cells that emigrated. Th e monoclonal antibody was used for immunohistochemical studies on R. p ipiens skin. Strong staining with the antibody was observed beneath th e basement membrane, in mucous glands, and in the subcutaneous tissue of the ventral skin. A weak staining was also observed in the ground s ubstances of both ventral and dorsal skin. These results confirm that a monoclonal antibody has been secured against at least one of the MIF constituents and that it is useful as a probe in detecting the distri bution of MIF in tissues. The results of its use in this study support the hypothesis that MIF plays a role in the expression, development, and maintenance of the dorsal-ventral pigmentation patterns of frogs. (C) 1995 Academic Press, Inc.