290
CHARLES Ε.
WILDE
role in pigment cell and ectomesenchyme differentiation in the urodele
neuro-epithelium explant system. The experiments were carried out in
several ways. In one, a known inhibitory analogue was incorporated in
the culture medium and test mixtures from which phenylalanine might
be synthesized were added to test whether the mixtures, like phenylalanine itself, could overcome the imposed inhibition. In another way, two
analogues, sterically different from each other, and each with inhibition
spectra supplementary to each other, were combined to test whether
metabolic exchange could be carried out by the neuro-epithelial cells
thus to synthesize phenylalanine and overcome both inhibitory effects.
(Thus Β-2 thienylalanine and phenyllactic acid were combined, each
compound being specifically inhibitory of one phase of neuro-epithelial
differentiation; the former active against ectomesenchyme differentiation and the latter against pigment cells). In still another test of the
requirement for the whole molecule in these differentiative processes,
analogue compounds such as phenylglycine and phenylserine were incorporated in the medium. The results of the experiments conformed
to a general pattern interpretable only in the light of the essentiality of
the whole molecule of phenylalanine, with unchanged steric specificity.
In these systems molecular phenylalanine in equimolar amounts was
able to overcome the inhibitory effects. In no case however, could
explanted pure neuro-epithelial cells utilize these mixtures to overcome
a pre-existing inhibition, or to synthesize phenylalanine.
An interesting result was obtained when neuro-epithelial cells were
co-cultured with archenteron roof mesoderm cells under the same
conditions. This experiment had been developed previously as a specificity control to demonstrate that the effects of these differentiation
inhibitors were directed solely against the differentiation metabolism of
the neuro-epithelium. Under these circumstances the effects of the
analogues, or mixtures were relieved as efficiently as with molecular
phenylalanine, and differentiation was normal in every respect. Thus
while the metabolic activities of the neuro-epithelium were unable to
utilize the test compounds and their differentiation was thereby
inhibited, the archenteron roof cells, without interference to their own
characteristic differentiation into striated muscle etc., were able to
metabolize these compounds and permit the differentiation of pigment
cells and ectomesenchyme. The presumption that the mesodermal
mechanism of inhibition relief was by the synthesis of phenylalanine
and the presentation of this molecular morphogen to the micro-environment of the neuro-epithelial cells was confirmed by repeating these
experiments with combinations of ventral ectoderm alone and with cocultured internal cells. Here again, where phenylalanine itself can elicit
pigment cells from pure ventral ectoderm, the analogues were only able
CHARLES Ε.
WILDE
role in pigment cell and ectomesenchyme differentiation in the urodele
neuro-epithelium explant system. The experiments were carried out in
several ways. In one, a known inhibitory analogue was incorporated in
the culture medium and test mixtures from which phenylalanine might
be synthesized were added to test whether the mixtures, like phenylalanine itself, could overcome the imposed inhibition. In another way, two
analogues, sterically different from each other, and each with inhibition
spectra supplementary to each other, were combined to test whether
metabolic exchange could be carried out by the neuro-epithelial cells
thus to synthesize phenylalanine and overcome both inhibitory effects.
(Thus Β-2 thienylalanine and phenyllactic acid were combined, each
compound being specifically inhibitory of one phase of neuro-epithelial
differentiation; the former active against ectomesenchyme differentiation and the latter against pigment cells). In still another test of the
requirement for the whole molecule in these differentiative processes,
analogue compounds such as phenylglycine and phenylserine were incorporated in the medium. The results of the experiments conformed
to a general pattern interpretable only in the light of the essentiality of
the whole molecule of phenylalanine, with unchanged steric specificity.
In these systems molecular phenylalanine in equimolar amounts was
able to overcome the inhibitory effects. In no case however, could
explanted pure neuro-epithelial cells utilize these mixtures to overcome
a pre-existing inhibition, or to synthesize phenylalanine.
An interesting result was obtained when neuro-epithelial cells were
co-cultured with archenteron roof mesoderm cells under the same
conditions. This experiment had been developed previously as a specificity control to demonstrate that the effects of these differentiation
inhibitors were directed solely against the differentiation metabolism of
the neuro-epithelium. Under these circumstances the effects of the
analogues, or mixtures were relieved as efficiently as with molecular
phenylalanine, and differentiation was normal in every respect. Thus
while the metabolic activities of the neuro-epithelium were unable to
utilize the test compounds and their differentiation was thereby
inhibited, the archenteron roof cells, without interference to their own
characteristic differentiation into striated muscle etc., were able to
metabolize these compounds and permit the differentiation of pigment
cells and ectomesenchyme. The presumption that the mesodermal
mechanism of inhibition relief was by the synthesis of phenylalanine
and the presentation of this molecular morphogen to the micro-environment of the neuro-epithelial cells was confirmed by repeating these
experiments with combinations of ventral ectoderm alone and with cocultured internal cells. Here again, where phenylalanine itself can elicit
pigment cells from pure ventral ectoderm, the analogues were only able