ULTRASTRUCTURAL DATA ON THE MELANOPHORES ASSOCIATED WITH THE CELLULARELASMOID SCALES IN LEPORINUS-FRIDERICI (TELEOSTEI, OSTARIOPHYSI, ANASTOMIDAE) - THEIR PUTATIVE PARTICIPATION IN SCALE MATRIX FORMATION

Transmission electron microscopic (TEM) examination of cellular scales of Leporinus friderici reveals the presence of melanophores associate d with the hyposquama, a continuous cellular layer lining the inner su rface of the scale. Hyposquamal scleroblasts synthesize the collagen f ibrils forming the scale matrix. Some scleroblasts lining the deep sur face of the scale margin become trapped within the collagenous matrix. Neighboring melanophores become inserted within the hyposquama. They contact the scale matrix and show morphological features resembling th ose of the adjacent hyposquamal scleroblasts with which they are conne cted and, like them, they appear to be involved in the production of t he collagenous scale matrix. The present ultrastructural study favors the hypothesis that melanophores in vivo are like tumorous cell lines in vitro in that they maintain a degree of plasticity allowing changes in their phenotype according to environmental conditions. The close m orpho-functional links between scale scleroblasts and melanophores sug gest that they could be closely related lineages derived from the same basic stem cells and support the hypothesis that scale scleroblasts a s well as melanophores are neural crest derivatives. (C) 1996 Wiley-Li ss, Inc.