VI.
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
297
cells. Neuron-like behaviour would not be expected. Van Haeften (1958)
has recently reported the development of masses of myoblasts on the
chick chorioallantoic membrane following the implantation of a pellet
of heart muscle cell free homogenate. Ebert (unpublished work) has
announced that a similar experiment with muscle microsomes failed in
his laboratory but that on mixture with Rous sarcoma virus (fowl
virus $ 1) the muscle microsome implant induced large masses of typical
cardiac muscle among the cells of the chorioallantois. Apparently the
virus acted as a carrier for the ribosomal information in a manner
similar to transduction phenomena in bacteria. Such a positive result
directs attention to a bypass of nuclear activities since the predominating
or currently active nuclear cues would tend to drive the cytoplasmic
machinery of chorioallantoic cells toward fibroblastic and epithelial
differentiations.
Ribosomal activities direct attention to the fact that cytoplasmic
particulates carry cogent directive information in contemporary cell
differentiation. Ribosomes are, of course, a biochemist's artificial cell
constituent and in all probability represent fragments of the endoplasmic
reticulum. If it is assumed for the moment that this cytoplasmic material
is the immediate directive agent of differentiative activities, there is
sufficient complexity in its major chemical constituent, ribosenucleoprotein to account for the large numbers of discrete cell types which
ultimately differentiate.
A ribosomal system must itself have an ontogeny. In conversion
experiments it is customary to 'infect' embryonic cells with particulates
from fully differentiated cells. These materials are presumably firmly
coded and would be expected to function with an efficiency surpassing
that found in the contemporarily younger host cells. The result of a
successful infection would be expressed by type specific differentiative
behaviour. The development of early ribosomal systems might be
expected to be characterized by much less efficient metabolic routings
which, when undisturbed, are sufficient to permit selective differentiation
cues to be fixed in differentiative pathways. Such early systems would
be easily affected by both environmental and nuclear effects, or both.
Under this interpretation the non-exclusiveness of the categories of
events just discussed would be the hypothesis of choice and through
time interactions of nucleus, cytoplasm (ribosomes) and molecular microenvironment would ultimately be manifested in normal differentiative
syntheses.
The vertebrate pigment cell would be expected to respond in this
manner, perhaps at one period appearing to respond to nuclear cues, at
another to micro-environmental ones, and at still another time responsive
to conversion through 'infective differentiation'.
DIFFERENTIATION OF VERTEBRATE PIGMENT CELLS
297
cells. Neuron-like behaviour would not be expected. Van Haeften (1958)
has recently reported the development of masses of myoblasts on the
chick chorioallantoic membrane following the implantation of a pellet
of heart muscle cell free homogenate. Ebert (unpublished work) has
announced that a similar experiment with muscle microsomes failed in
his laboratory but that on mixture with Rous sarcoma virus (fowl
virus $ 1) the muscle microsome implant induced large masses of typical
cardiac muscle among the cells of the chorioallantois. Apparently the
virus acted as a carrier for the ribosomal information in a manner
similar to transduction phenomena in bacteria. Such a positive result
directs attention to a bypass of nuclear activities since the predominating
or currently active nuclear cues would tend to drive the cytoplasmic
machinery of chorioallantoic cells toward fibroblastic and epithelial
differentiations.
Ribosomal activities direct attention to the fact that cytoplasmic
particulates carry cogent directive information in contemporary cell
differentiation. Ribosomes are, of course, a biochemist's artificial cell
constituent and in all probability represent fragments of the endoplasmic
reticulum. If it is assumed for the moment that this cytoplasmic material
is the immediate directive agent of differentiative activities, there is
sufficient complexity in its major chemical constituent, ribosenucleoprotein to account for the large numbers of discrete cell types which
ultimately differentiate.
A ribosomal system must itself have an ontogeny. In conversion
experiments it is customary to 'infect' embryonic cells with particulates
from fully differentiated cells. These materials are presumably firmly
coded and would be expected to function with an efficiency surpassing
that found in the contemporarily younger host cells. The result of a
successful infection would be expressed by type specific differentiative
behaviour. The development of early ribosomal systems might be
expected to be characterized by much less efficient metabolic routings
which, when undisturbed, are sufficient to permit selective differentiation
cues to be fixed in differentiative pathways. Such early systems would
be easily affected by both environmental and nuclear effects, or both.
Under this interpretation the non-exclusiveness of the categories of
events just discussed would be the hypothesis of choice and through
time interactions of nucleus, cytoplasm (ribosomes) and molecular microenvironment would ultimately be manifested in normal differentiative
syntheses.
The vertebrate pigment cell would be expected to respond in this
manner, perhaps at one period appearing to respond to nuclear cues, at
another to micro-environmental ones, and at still another time responsive
to conversion through 'infective differentiation'.