Role of the dermal tracts in the pigment pattern of the frog.

The pigment pattern of the ventral skin of the frog Rana esculenta is compared in skin fragments grown for 24 hr with or without antiserum directed to fibronectin (anti-FN). Melanocyte-stimulating hormone (MSH) was added to the medium during the last hour in culture in order to enhance visibility of melanophores in the ventral region of the frog skin. Comparison of these two treatments provides information regarding the precise localization of melanophores in the dermal tracts and their involvement in the pigment pattern of the ventral frog skin. In this regard, the whitish pigment pattern of skin fragments is compared to the tiny black spots found on anti-FN treated skin fragments and the abundant blotchy spots found on skin cultured alone. The distribution of melanophores in the dermal tracts observed in vertical semithin sections is found to be related to the three different levels of the dermal tracts. This report demonstrates the importance of fibronectin as a substrate for the melanophore migration, the importance of the tract level for the melanophore localization both involved in the pigment pattern of the ventral skin.