16
TUNEO
YAMADA
the marginal zone of the early gastrula of Triturus pyrrhogaster isolated
in Holtfreter solution differentiated into ventral and lateral mesodermal
structures such as blood island, mesothelium, and nephric tubules
(Yamada, 1950a; cf. Fernald, 1943). When the same area was treated
immediately after isolation with an ammonia solution for a few minutes,
transferred to Holtfreter's solution, and then cultured, notochord and
somites were frequently formed while the frequency of blood island and
mesothelium was significantly lower than in the control series (Yamada,
1950a). The array of structures formed by the treated ventral mesoderm
corresponds to that formed by the isolated dorsal marginal zone, i.e. the
organizer area. Thus, the mode of differentiation of the isolated marginal
zone is shifted from the ventral type to the dorsal by the ammonia
treatment. It was proposed to designate this type of shift in the mode
of differentiation as 'dorsalization'. It is clear that the effects of the
ammonia treatment on the isolated ectoderm can also be called dorsalization, because the epidermal differentiation is characteristic of the
ventral half of the presumptive ectoderm area and the neural, mesectodermal, and placodal differentiations are characteristic of the dorsal
half of the same area.
Later similar dorsalizing effects on the presumptive ventral mesoderm
were ascertained for lactic acid by Kawakami and Okano (1955), and
for sodium thiocyanate, sodium iodate, urea, hydrochloric acid, and
zinc chloride by Ogi (1958b). Most of the chemicals are known to be
also capable of dorsalizing the ectoderm. Thus it has been established
that the presumptive ventral mesoderm dorsalized by various injurious
agents is equivalent in mode of differentiation to the organizer. The next
question to be asked is whether the ventral marginal zone treated with
these agents is equivalent to the organizer also in inducing ability. An
affirmative answer was obtained by Ogi (1958b) who showed that the
medio-ventral marginal zone of the Triturus gastrula treated with
ammonia, thiocyanate, iodate, urea, hydrochloric acid, and zinc chloride
is able to induce various structures belonging to the spino-caudal,
deuterencephalic, and archencephalic types in the presumptive ectoderm
added to it, after the treatment with the agents and reaggregation.
Thus treatment of the ventral marginal zone with these agents, not only
alters the mode of differentiation, but also activates the regional
inducing ability. In other words, the ventral marginal zone can be
converted into the organizer by these treatments. Dorsalization by
subcytolytic treatments is also possible in the ectoderm of the Anura:
Karasaki and Yamada (1955) using a high pH shock and Flickinger
(1957) using a C0 2 shock obtained archencephalic or neural differentiation in the ectoderm of Banapipiens.
According to Ranzi (1957a, b), in sea-urchin development the animal
TUNEO
YAMADA
the marginal zone of the early gastrula of Triturus pyrrhogaster isolated
in Holtfreter solution differentiated into ventral and lateral mesodermal
structures such as blood island, mesothelium, and nephric tubules
(Yamada, 1950a; cf. Fernald, 1943). When the same area was treated
immediately after isolation with an ammonia solution for a few minutes,
transferred to Holtfreter's solution, and then cultured, notochord and
somites were frequently formed while the frequency of blood island and
mesothelium was significantly lower than in the control series (Yamada,
1950a). The array of structures formed by the treated ventral mesoderm
corresponds to that formed by the isolated dorsal marginal zone, i.e. the
organizer area. Thus, the mode of differentiation of the isolated marginal
zone is shifted from the ventral type to the dorsal by the ammonia
treatment. It was proposed to designate this type of shift in the mode
of differentiation as 'dorsalization'. It is clear that the effects of the
ammonia treatment on the isolated ectoderm can also be called dorsalization, because the epidermal differentiation is characteristic of the
ventral half of the presumptive ectoderm area and the neural, mesectodermal, and placodal differentiations are characteristic of the dorsal
half of the same area.
Later similar dorsalizing effects on the presumptive ventral mesoderm
were ascertained for lactic acid by Kawakami and Okano (1955), and
for sodium thiocyanate, sodium iodate, urea, hydrochloric acid, and
zinc chloride by Ogi (1958b). Most of the chemicals are known to be
also capable of dorsalizing the ectoderm. Thus it has been established
that the presumptive ventral mesoderm dorsalized by various injurious
agents is equivalent in mode of differentiation to the organizer. The next
question to be asked is whether the ventral marginal zone treated with
these agents is equivalent to the organizer also in inducing ability. An
affirmative answer was obtained by Ogi (1958b) who showed that the
medio-ventral marginal zone of the Triturus gastrula treated with
ammonia, thiocyanate, iodate, urea, hydrochloric acid, and zinc chloride
is able to induce various structures belonging to the spino-caudal,
deuterencephalic, and archencephalic types in the presumptive ectoderm
added to it, after the treatment with the agents and reaggregation.
Thus treatment of the ventral marginal zone with these agents, not only
alters the mode of differentiation, but also activates the regional
inducing ability. In other words, the ventral marginal zone can be
converted into the organizer by these treatments. Dorsalization by
subcytolytic treatments is also possible in the ectoderm of the Anura:
Karasaki and Yamada (1955) using a high pH shock and Flickinger
(1957) using a C0 2 shock obtained archencephalic or neural differentiation in the ectoderm of Banapipiens.
According to Ranzi (1957a, b), in sea-urchin development the animal