VI.
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
293
slow. Another phenomenon was observed in the washed cells, a certain
percentage apparently differentiated along two lines at one time.
Certain cells appeared stellate with clear peripheral processes and
intense melanin synthesis in the perinuclear area. However, close
observation of the non-pigmented stellate processes showed unequivocal
development of cross-striated myofibrils filling the clear areas. Such
cells apparently differentiated peripherally with the stellate pattern of
a pigment cell, also peripherally as striated muscle, while centrally, in
the perinuclear area melanogenesis typical of a pigment cell was undertaken at the same time. These have been called 'confused cells'. In other
cases, neurone-like cells developed long axonal processes with typical
ameboid tips while undertaking intense melanogenesis in the perinuclear
area. Further cases could be cited. It would appear in the absence of
morphogenetic chemical cues present in the micro-environment, that
cells attempt to restore this lack by synthetic and secretory activities.
The reconstitution of E.C.M. is temporally incomplete and the response
in differentiation of the cells so affected is erratic, incomplete, or may be
in two distinct and different pathways at one and the same time. Such
an imbalance must be imputed to the loss of E.C.M. Therefore, E.C.M.
must be able to carry and to transfer local differentiation cues to which
cells must respond in order to differentiate in an orderly way along
unique pathways. Failing this response or failing the presence of the
cues, the cells may exercise several responses at once, following attempted
restoration of the proper milieu.
Here again the response of cells in differentiation is cued by effects
in the micro-environment to which cells react by metabolic changes
leading to those discrete cytoplasmic syntheses which result in differentiative changes.
From the data at hand there is reason to conclude that the differentiation of the vertebrate pigment cell lies initially in the development of
proper syntheses in response to cues coming to it from its particular
micro-environment. The nature of the cues is obscure in a large sense.
Perhaps the presentation of the phenylalanine cue to the urodele neuroepithelium by the underlying archenteron roof mesoderm is best interpreted in this light. There must be many cues and surely no cue is unitary
but represents a complex ratio of appropriate metabolites of large and
small molecular weight.
VI. Discussion and Conclusion
Vertebrate pigment cells differentiate in appropriate time co-ordinates
and topographical co-ordinates in the flow of events in embryogenesis.
Within this framework the specific synthetic machinery develops, func-
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
293
slow. Another phenomenon was observed in the washed cells, a certain
percentage apparently differentiated along two lines at one time.
Certain cells appeared stellate with clear peripheral processes and
intense melanin synthesis in the perinuclear area. However, close
observation of the non-pigmented stellate processes showed unequivocal
development of cross-striated myofibrils filling the clear areas. Such
cells apparently differentiated peripherally with the stellate pattern of
a pigment cell, also peripherally as striated muscle, while centrally, in
the perinuclear area melanogenesis typical of a pigment cell was undertaken at the same time. These have been called 'confused cells'. In other
cases, neurone-like cells developed long axonal processes with typical
ameboid tips while undertaking intense melanogenesis in the perinuclear
area. Further cases could be cited. It would appear in the absence of
morphogenetic chemical cues present in the micro-environment, that
cells attempt to restore this lack by synthetic and secretory activities.
The reconstitution of E.C.M. is temporally incomplete and the response
in differentiation of the cells so affected is erratic, incomplete, or may be
in two distinct and different pathways at one and the same time. Such
an imbalance must be imputed to the loss of E.C.M. Therefore, E.C.M.
must be able to carry and to transfer local differentiation cues to which
cells must respond in order to differentiate in an orderly way along
unique pathways. Failing this response or failing the presence of the
cues, the cells may exercise several responses at once, following attempted
restoration of the proper milieu.
Here again the response of cells in differentiation is cued by effects
in the micro-environment to which cells react by metabolic changes
leading to those discrete cytoplasmic syntheses which result in differentiative changes.
From the data at hand there is reason to conclude that the differentiation of the vertebrate pigment cell lies initially in the development of
proper syntheses in response to cues coming to it from its particular
micro-environment. The nature of the cues is obscure in a large sense.
Perhaps the presentation of the phenylalanine cue to the urodele neuroepithelium by the underlying archenteron roof mesoderm is best interpreted in this light. There must be many cues and surely no cue is unitary
but represents a complex ratio of appropriate metabolites of large and
small molecular weight.
VI. Discussion and Conclusion
Vertebrate pigment cells differentiate in appropriate time co-ordinates
and topographical co-ordinates in the flow of events in embryogenesis.
Within this framework the specific synthetic machinery develops, func-