4
TUNEO
YAMADA
during the early phase of development. In Triturus pyrrhogaster,
mitochondria of the presumptive ectoderm cells of the earliest gastrula
are represented by spheroids or ovoids with diameter varying from
0-3 to 0-7 μ. Cristae are few and only incompletely formed. At this stage
and earlier, beside mitochondria a number of smaller darker spheroids
without internal septa are observed and provisionally called dense
bodies. According to Karasaki they may represent the precursor of
mitochondria. In the late gastrula of Triturus, when the presumptive
ectoderm is underlain by the organizer layer, the presumptive neural
cells show rod-shaped or long oval mitochondria as well as spherical
ones. In the rod-shaped mitochondria, cristae are conspicuously formed
but in small numbers, leaving a wide space between individual cristae.
Later in the neurula, the mitochondria of the neural plate cells are
larger in number and size compared with those of the preceding stages.
Many filamentous mitochondria furnished internally with numerous
cristae are present. The tendency to structural elaboration is further
accentuated in the cells of the wall of the spinal cord of the tail-bud
stage. Here, mitochondria as long as 6 μ can be seen often forming a
dense group. The matrix of the mitochondrion is denser than earlier, and
a complicated system of cristae fills up the interior. According to Eakin
and Lehmann (1957) a similar transformation also occurs in the
mitochondrial population in the neural cell-line in the embryo of
Xenopus laevis.
In Triturus, the change in the mitochondrial population in number
and structure found in cells of the epidermal region during gastrulation
and neurulation is less pronounced than that in the neural region
(Karasaki, 1959a).
As it is very probable that the enzymatic activities of a mitochondrion
are dependent upon the area of its membranes, especially of cristae, the
conclusion that the morphological elaboration of the mitochondrial
population observed in the neural cell-line during the phase of induction
and differentiation reflects the rise in the biochemical activity of the
population appears unavoidable. In this respect, the findings of Boell
and Weber (1955) are important; they isolated the mitochondrial
fraction from the Xenopus embryo and found an appreciable increase in
its cytochrome oxidase activity (per h per/xgN) during early development.
According to unpublished data of Karasaki, the cells of the invaginating organizer area (the dorsal mesoderm) of the earliest gastrula of
Triturus contain beside spheroidal or ellipsoidal mitochondria, a number
of elongated mitochondria with cristae, which are almost absent in the
ectodermal cells of the same stage (Figs. 1 and 2). On the other hand,
the cells of the ventral mesoderm, which is not yet invaginating at this
stage, do not show such elongated mitochondria. This finding, together
TUNEO
YAMADA
during the early phase of development. In Triturus pyrrhogaster,
mitochondria of the presumptive ectoderm cells of the earliest gastrula
are represented by spheroids or ovoids with diameter varying from
0-3 to 0-7 μ. Cristae are few and only incompletely formed. At this stage
and earlier, beside mitochondria a number of smaller darker spheroids
without internal septa are observed and provisionally called dense
bodies. According to Karasaki they may represent the precursor of
mitochondria. In the late gastrula of Triturus, when the presumptive
ectoderm is underlain by the organizer layer, the presumptive neural
cells show rod-shaped or long oval mitochondria as well as spherical
ones. In the rod-shaped mitochondria, cristae are conspicuously formed
but in small numbers, leaving a wide space between individual cristae.
Later in the neurula, the mitochondria of the neural plate cells are
larger in number and size compared with those of the preceding stages.
Many filamentous mitochondria furnished internally with numerous
cristae are present. The tendency to structural elaboration is further
accentuated in the cells of the wall of the spinal cord of the tail-bud
stage. Here, mitochondria as long as 6 μ can be seen often forming a
dense group. The matrix of the mitochondrion is denser than earlier, and
a complicated system of cristae fills up the interior. According to Eakin
and Lehmann (1957) a similar transformation also occurs in the
mitochondrial population in the neural cell-line in the embryo of
Xenopus laevis.
In Triturus, the change in the mitochondrial population in number
and structure found in cells of the epidermal region during gastrulation
and neurulation is less pronounced than that in the neural region
(Karasaki, 1959a).
As it is very probable that the enzymatic activities of a mitochondrion
are dependent upon the area of its membranes, especially of cristae, the
conclusion that the morphological elaboration of the mitochondrial
population observed in the neural cell-line during the phase of induction
and differentiation reflects the rise in the biochemical activity of the
population appears unavoidable. In this respect, the findings of Boell
and Weber (1955) are important; they isolated the mitochondrial
fraction from the Xenopus embryo and found an appreciable increase in
its cytochrome oxidase activity (per h per/xgN) during early development.
According to unpublished data of Karasaki, the cells of the invaginating organizer area (the dorsal mesoderm) of the earliest gastrula of
Triturus contain beside spheroidal or ellipsoidal mitochondria, a number
of elongated mitochondria with cristae, which are almost absent in the
ectodermal cells of the same stage (Figs. 1 and 2). On the other hand,
the cells of the ventral mesoderm, which is not yet invaginating at this
stage, do not show such elongated mitochondria. This finding, together