VI.
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
271
terms of ability of transplanted anuran nuclei to cue the embryogenesis
of a complete normal embryo and tadpole, certain nuclei from specific
areas are unable to supply a complete embryogenetic set of cues. The
faults found in the embryos so reared are standard and repeatable.
Furthermore, an Τ χ ' generation of nuclei from defective embryos transplanted into enucleated eggs led to the development of embryos with
similar deficiencies.
The evidence for nuclear differentials upon which to construct
hypotheses for cellular differentiation is still inadequate in the face of
formal genetics. A still more cogent reason for hesitation in this regard
is to be found in the newer data on the conversion of cells from one
differentiated type to another and recent evidence that certain 'confused
cells' may differentiate in two discrete directions at once (Wilde, unpublished data). (See note added in proof.)
The cytoplasm with all of its associated particulate structures,
although the immediate seat of the overt syntheses concerned with the
differentiation process remains a dynamic yet mysterious hinterland
between the nucleus and the non-protoplasmic environment. The cytoplasm contains the biochemical materials and structures whereby cells
undertake particular functions and whereby the cell type is recognized
by the investigator. There is evidence for the exchange of materials
between nucleus and cytoplasm (Gay, 1955, 1956) and between cytoplasm and its immediate micro-environment (Moscona, 1959).
Whereas there are means for testing the potentialities in terms of
differentiation of the nucleus (vide supra) and, as will be demonstrated
below, the micro-environment provides an excellent test site, the cytoplasm has only rarely been freed from the contaminating metabolic
influences of the nucleus. Therefore, independent differentiative capacities of cytoplasm must be considered in the light of contamination by
agencies of nuclear or environmental origin.
Ε. B. Harvey (1936), demonstrated that enucleate halves of the eggs
of Arbacia punctulata could be stimulated parthenogenetically with the
production of enucleate blastulae. Development stopped at this point
but the blastulae became ciliated. In this instance the cytoplasm was
able to mediate the synthesis of cilia, relatively complex cellular
organelles in the contemporary absence of informational cues, or
biochemical syntheses stemming from the nucleus. The cytoplasm must
obviously have been the seat of the whole differentiative process. In the
author's laboratory the development of ciliated pieces of cytoplasm
fragmented from disaggregated urodele blástula and gastrula cells has
been observed. Further evidence of the role of enucleate cytoplasm in
pigment 'cell' differentiation will be presented below.
The environment within which cells live, synthesize and from which
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
271
terms of ability of transplanted anuran nuclei to cue the embryogenesis
of a complete normal embryo and tadpole, certain nuclei from specific
areas are unable to supply a complete embryogenetic set of cues. The
faults found in the embryos so reared are standard and repeatable.
Furthermore, an Τ χ ' generation of nuclei from defective embryos transplanted into enucleated eggs led to the development of embryos with
similar deficiencies.
The evidence for nuclear differentials upon which to construct
hypotheses for cellular differentiation is still inadequate in the face of
formal genetics. A still more cogent reason for hesitation in this regard
is to be found in the newer data on the conversion of cells from one
differentiated type to another and recent evidence that certain 'confused
cells' may differentiate in two discrete directions at once (Wilde, unpublished data). (See note added in proof.)
The cytoplasm with all of its associated particulate structures,
although the immediate seat of the overt syntheses concerned with the
differentiation process remains a dynamic yet mysterious hinterland
between the nucleus and the non-protoplasmic environment. The cytoplasm contains the biochemical materials and structures whereby cells
undertake particular functions and whereby the cell type is recognized
by the investigator. There is evidence for the exchange of materials
between nucleus and cytoplasm (Gay, 1955, 1956) and between cytoplasm and its immediate micro-environment (Moscona, 1959).
Whereas there are means for testing the potentialities in terms of
differentiation of the nucleus (vide supra) and, as will be demonstrated
below, the micro-environment provides an excellent test site, the cytoplasm has only rarely been freed from the contaminating metabolic
influences of the nucleus. Therefore, independent differentiative capacities of cytoplasm must be considered in the light of contamination by
agencies of nuclear or environmental origin.
Ε. B. Harvey (1936), demonstrated that enucleate halves of the eggs
of Arbacia punctulata could be stimulated parthenogenetically with the
production of enucleate blastulae. Development stopped at this point
but the blastulae became ciliated. In this instance the cytoplasm was
able to mediate the synthesis of cilia, relatively complex cellular
organelles in the contemporary absence of informational cues, or
biochemical syntheses stemming from the nucleus. The cytoplasm must
obviously have been the seat of the whole differentiative process. In the
author's laboratory the development of ciliated pieces of cytoplasm
fragmented from disaggregated urodele blástula and gastrula cells has
been observed. Further evidence of the role of enucleate cytoplasm in
pigment 'cell' differentiation will be presented below.
The environment within which cells live, synthesize and from which