Avian neural crest cells express a melanogenic trait during early migration from the neural tube: observations with the new monoclonal antibody, "MEBL-1"

A new monoclonal antibody, MEBL-1, which specifically recognizes melanocytes and their precursors, was used to examine the differentiation of neural crest cells into melanocytes in situ. MEBL-1-positive precursors of melanocytes in the trunk were first detected in mesenchyme located above the neural tube at the level of a wing bud at stage 19, when active migration of neural crest cells along the ventral route was almost complete. DiO-labelled neural crest cells, which begin to emigrate from the neural tube at stages 17-18 and then migrate along the dorsolateral route, were found to become MEBL-1-positive. This indicates that MEBL-1 antigens are expressed by neural crest cells immediately following their emigration and neural crest cells become melanogenic. Expression of the MEBL-1 antigens was followed by decrease in, and finally the loss of, HNK-1 antigen expression. At the cephalic level, MEBL-1-positive precursors of melanocytes were first detected in mesenchyme located above the dorsal side of the mesencephalic neural tube at stage 16. At the vagal level, the precursors were noted first in mesenchyme located above the dorsal side of the rhombencephalic neural tube at stage 18. MEBL-1 reacted with the cell membrane and premelanosome-like granules in addition to the nuclear membrane, endoplasmic reticulum and Golgi apparatus of the migratory precursors. The antigens recognized by MEBL-1 were proteins with relative molecular masses of 135 x 10 and 115 x 10. We suggest that MEBL-1 may be the earliest marker for melanogenic neural crest cells.