46
TUNEO
YAMADA
within the amphibian gastrula: RNA/total nitrogen (Takata, 1953);
total earbohydrate/total nitrogen (Gregg and L0vtrup, 1950); glycogen/
dry weight (Heatley and Lindahl, 1937); dipeptidase activity/dry weight
(Barth and Sze, 1953); /S-glycerophosphatase/total nitrogen (Gregg and
L0vtrup, 1950). It is also probable that content of SH groups (Brächet,
1942); intensity of reduction of vital dyes (Piepho, 1938; Child, 1948);
ATP/dry weight, apyrase/dry weight (Fujii et al., 1951); catheptic
activity/total nitrogen (D'Amelio and Ceas, 1957); catheptic activity/
dry weight (Deuchar, 1958) fall in the same category. Although
participation of many of the enzymes and substances listed above in the
biochemical processes connected with organizer action is unquestionable,
it is unlikely that the distinctive morphogenetic ability of the organizer
can be elucidated simply by means of a gradient of this type. There may
be some metabolic events which distinguish the organizer area from all
other areas at the onset of gastrulation. In this respect the pattern of
utilization of glycogen is interesting. As stated above, the distribution
of glycogen itself shows the usual pattern of the animal-vegetal and
dorso-ventral gradients. However, glycogenolysis was found to occur
first in the dorsal marginal zone during invagination, and later in the
ventral marginal zone, always in parallel with the invagination process
(Heatley and Lindahl, 1937; Jaeger, 1945). Further data of Jaeger
indicated that in spite of the close connection between glycogenolysis
and invagination, induction does occur without concomitant glycogenolysis. The explanted dorsal marginal zone which is capable of
differentiating into notochord, somites, etc., and of inducing neural
structures in the ectodermal pieces added to it, fails to show glycogenolysis. Thus, disappearance of glycogen seems to be indispensable
for morphogenetic movements by which the area comes in contact with
the dorsal ectoderm and forms the archenteron, but not indispensable
for its inducing and differentiating abilities. It should, however, be
pointed out that the possibility of a role for glycogenolysis in determining the regional nature of differentiation and induction has not been
ruled out.
Another metabolic event which may characterize the organizer area
is indicated by isotope experiments conducted by Sirlin and Waddington
(1954), and Sirlin (1955). According to these authors the uptake of
glycine-214
C and d?-methionine35
S during gastrulation, as judged by
autoradiography, is most intensive in the nuclei of the dorsal marginal
zone and its derivatives, and is detectable also in the nuclei of the neural
plate. Although at this stage cell division requires the increase of nuclear
material but no increase of cytoplasmic material, it is unlikely that the
observed pattern can be ascribed to differential mitotic activity. It is
more likely that the high activity in the nuclei of the dorsal mesoderm
TUNEO
YAMADA
within the amphibian gastrula: RNA/total nitrogen (Takata, 1953);
total earbohydrate/total nitrogen (Gregg and L0vtrup, 1950); glycogen/
dry weight (Heatley and Lindahl, 1937); dipeptidase activity/dry weight
(Barth and Sze, 1953); /S-glycerophosphatase/total nitrogen (Gregg and
L0vtrup, 1950). It is also probable that content of SH groups (Brächet,
1942); intensity of reduction of vital dyes (Piepho, 1938; Child, 1948);
ATP/dry weight, apyrase/dry weight (Fujii et al., 1951); catheptic
activity/total nitrogen (D'Amelio and Ceas, 1957); catheptic activity/
dry weight (Deuchar, 1958) fall in the same category. Although
participation of many of the enzymes and substances listed above in the
biochemical processes connected with organizer action is unquestionable,
it is unlikely that the distinctive morphogenetic ability of the organizer
can be elucidated simply by means of a gradient of this type. There may
be some metabolic events which distinguish the organizer area from all
other areas at the onset of gastrulation. In this respect the pattern of
utilization of glycogen is interesting. As stated above, the distribution
of glycogen itself shows the usual pattern of the animal-vegetal and
dorso-ventral gradients. However, glycogenolysis was found to occur
first in the dorsal marginal zone during invagination, and later in the
ventral marginal zone, always in parallel with the invagination process
(Heatley and Lindahl, 1937; Jaeger, 1945). Further data of Jaeger
indicated that in spite of the close connection between glycogenolysis
and invagination, induction does occur without concomitant glycogenolysis. The explanted dorsal marginal zone which is capable of
differentiating into notochord, somites, etc., and of inducing neural
structures in the ectodermal pieces added to it, fails to show glycogenolysis. Thus, disappearance of glycogen seems to be indispensable
for morphogenetic movements by which the area comes in contact with
the dorsal ectoderm and forms the archenteron, but not indispensable
for its inducing and differentiating abilities. It should, however, be
pointed out that the possibility of a role for glycogenolysis in determining the regional nature of differentiation and induction has not been
ruled out.
Another metabolic event which may characterize the organizer area
is indicated by isotope experiments conducted by Sirlin and Waddington
(1954), and Sirlin (1955). According to these authors the uptake of
glycine-214
C and d?-methionine35
S during gastrulation, as judged by
autoradiography, is most intensive in the nuclei of the dorsal marginal
zone and its derivatives, and is detectable also in the nuclei of the neural
plate. Although at this stage cell division requires the increase of nuclear
material but no increase of cytoplasmic material, it is unlikely that the
observed pattern can be ascribed to differential mitotic activity. It is
more likely that the high activity in the nuclei of the dorsal mesoderm