VI.
DIFFERENTIATION OF VERTEBRATE
PIGMENT CELLS
269
future prospectives in the study of vertebrate pigmented cells. The
analysis will be based on selected morphological, physiological and
biochemical data of diverse source. It will be limited to a discussion of
normal pigment cell development and differentiation. Only rarely will
data from the important area of abnormal pigment cell biology be
referred to as it seems immediately relevant to the central theme.
II. The General Problem of Cellular Differentiation
Embryonic cells are distinguished from other cell types by the fact
that they pass through a series of processes whereby their later state
becomes recognizably different in morphology and in function. The
processes through which these differences are accomplished constitute
the acts of cellular differentiation. The major events concern changes in
protein synthesis and accessory metabolism. These result in the establishment of relatively specific and unique biochemical functions in the
diverging cells. Little, indeed, is known of the pathways whereby the
more well known general energetics metabolism, common to all cells, is
shunted into particular drive paths leading to these specific syntheses.
Specific syntheses are ultimately the hallmarks of particular cell types.
Cells are altered morphologically and biochemically by the shifts in
synthesis and the result is often apparent to the observer. Thus there
are characteristics which render recognizable erythrocytes, muscle cells,
pigment cells and many other types. Embryonic cells are commonly
considered, on the basis of a large bulk of evidence, to have, at particular
times, several pathways of differentiation open to them. This evidence,
though at present inordinately large in the bulk, is still of a highly
selective nature. The major portion of the evidence is derived from
studies of amphibian embryo development, with the teleost embryo and
the avian embryo as secondary sources. The mammalian embryo is
still relatively poorly studied. It is not intended here to decry these
differentials in depth or detail of analysis but to emphasize the unavoidably selective and incomplete nature of the data available at
present.
Cellular differentiation does occur. It is an observable process. It is
fundamentally a biochemical process whose intermediate details are
for the moment obscure. Although there may remain many sites of
differentiation not presently understood in the embryonic cell, it has
proven convenient for the present to divide sources of events resulting
in differentiative processes in embryogenesis into those of fundamental
origin within the living protoplasm of the cell and those from without,
that is stemming from the immediate micro-environment of molecular
species within which the mass of protoplasm exists. That integration
DIFFERENTIATION OF VERTEBRATE
PIGMENT CELLS
269
future prospectives in the study of vertebrate pigmented cells. The
analysis will be based on selected morphological, physiological and
biochemical data of diverse source. It will be limited to a discussion of
normal pigment cell development and differentiation. Only rarely will
data from the important area of abnormal pigment cell biology be
referred to as it seems immediately relevant to the central theme.
II. The General Problem of Cellular Differentiation
Embryonic cells are distinguished from other cell types by the fact
that they pass through a series of processes whereby their later state
becomes recognizably different in morphology and in function. The
processes through which these differences are accomplished constitute
the acts of cellular differentiation. The major events concern changes in
protein synthesis and accessory metabolism. These result in the establishment of relatively specific and unique biochemical functions in the
diverging cells. Little, indeed, is known of the pathways whereby the
more well known general energetics metabolism, common to all cells, is
shunted into particular drive paths leading to these specific syntheses.
Specific syntheses are ultimately the hallmarks of particular cell types.
Cells are altered morphologically and biochemically by the shifts in
synthesis and the result is often apparent to the observer. Thus there
are characteristics which render recognizable erythrocytes, muscle cells,
pigment cells and many other types. Embryonic cells are commonly
considered, on the basis of a large bulk of evidence, to have, at particular
times, several pathways of differentiation open to them. This evidence,
though at present inordinately large in the bulk, is still of a highly
selective nature. The major portion of the evidence is derived from
studies of amphibian embryo development, with the teleost embryo and
the avian embryo as secondary sources. The mammalian embryo is
still relatively poorly studied. It is not intended here to decry these
differentials in depth or detail of analysis but to emphasize the unavoidably selective and incomplete nature of the data available at
present.
Cellular differentiation does occur. It is an observable process. It is
fundamentally a biochemical process whose intermediate details are
for the moment obscure. Although there may remain many sites of
differentiation not presently understood in the embryonic cell, it has
proven convenient for the present to divide sources of events resulting
in differentiative processes in embryogenesis into those of fundamental
origin within the living protoplasm of the cell and those from without,
that is stemming from the immediate micro-environment of molecular
species within which the mass of protoplasm exists. That integration