Overview on the melanocyte precursor migration from neural crest

In vertebrates, melanocytes in the trunk region originate from the neural crest as a member of pluripotent cells during the developmental process. Melanoblasts, a precursor of melanocytes, have been known to originate from the neural crest, migrate through the dorsolateral pathway and settle in the body's integument. But recently, in the lower vertebrates, many pigment cells are found in pleura, intestine and connective tissues, etc. in addition to skin, feather or scales. These pigment cells in the internal body are thought to migrate through the dorsovental pathway and locate in the inner organs and connective tissues. Even in many lines of chicken or wild quail, we found considerable numbers of melanocytes in the inner organs. Furthermore, the unique chicken, Silky, is known to display the ectopic hyperpigmentation in the internal organs (Fibromelanosis; Fm). In the Silky chicken, huge numbers of melanoblasts migrate through the dorsoventral pathway and proliferate in the inner organs. To understand the gene responsible for Fm, we mapped it as 1.64Mb on chromosome 20. Furthermore, we also detected a Silky specific duplicate region with 130 Kb in the area. Endothelin 3 is included in the region and shows a two-fold expression compared to the wild type. Endothelin 3 is known as a strong mitogen for melanoblast and it is supposed to be the responsible gene of Fm. Here we summarize the involvement of the paracrine or autocrine factors from the environment and dorsoventral pathway during pigment cells migration and differentiation. In this review, we will describe and discuss the melanocyte differentiation process from recent reports and our data using fish and chicken, that is, 1) melanoblast-migration through both pathways from the neural crest, 2) differentiation to melanocytes, 3) factors involved in these processes of pigment cells.