This thesis is concerned with melanocyte differentiation of the neural crest cells in
the embryonic Brown Leghorn fowl (Gallus gallusl Melanocyte differentiation in vivo
was compared with that occurring in three experimental systems in vitro . Premigratory
neural crest cells were isolated by the neural tube explanation technique of Cohen
and Konisberg (1975). Differentiation of these isolated cells was compared with that
which occurred in the postmigratory crest cells of the periorbital mesenchyme and
Examination of melanocyte shape in vivo demonstrated that cell shape is extrinsically
determined by features of the local micro-environment contrary to what has been reported
in the mouse tissue. Observations of melanocyte shape change in vitro indicated that
the environmental control of shape occurs by modulation of locomotory activity.
Melanogenesis within isolated cells was found to be different from that occurring in
mesenchymal explants, or connective tissues and ocular epithelia in vivo. The isolated
melanoblasts produced an ultrastructurally abnormal brown melanosome with an altered
elemental composition, whereas those cells which differentiated within ocular tissue or
mesenchymal explants produced black eumelanosomes.
The group of cells which colonise the corneal stroma are not totally committed to their
fate as fibroblasts at the time of migration from the orbital mesenchyme. Some of the
migratory cells retain the ability to become melanocytes, although this is rapidly
lost after stromal colonisation.
Finally, melanocyte and fibroblast differentiationare presented as alternatives within
the pigmented mesenchyme and attention is drawn to the fact that the abnormally
pigmented crest cells in vitro resemble human malignant melanoma cells.