EMBRYONIC HEMOGLOBIN SYNTHESIS
107
Brauns (1940). The usual "defect" and "isolation" experiments were
carried out in all these studies, and the results showed quite clearly the
ventral mesoderm has assumed its potential erythropoietic function by
the neurula stage, determination probably taking place during gastrula
stages. Hb can be detected by benzidine staining at the tailbud stage
(Slonimski, 1931). Pantelouris et al (1963) injected females of Xenopus
with Fe
59
and studied the localization of Fe
59
in the oocytes and embryos
from the injected female. Fe
59
is diffusely distributed over the whole
embryo at the blastula stage, but a definite gradient appears in late
blastula and early gastrula embryos, with heavier labeling in the ventral
portions of the embryo, especially the endoderm and adjacent mesoderm.
This conforms to the embryological expectations. Brown and Caston
(1962) have isolated the iron storage protein, ferritin, from eggs of
Rana pipiens.
Throneberry and Shaver (1962) applied immunological methods to the
question of when Hb first forms in frog embryos. They report in their
abstract that they obtained specific antibodies against adult Hb. They
claim globin was found in extracts from all stages, even body cavity
eggs, but heme was not detectable until hatching.
The effect of agents affecting RNA metabolism on amphibian embryos
has been investigated. One such agent, actinomycin D, is very toxic, and
death, developmental arrest, and cytolysis ensue. Flickinger (1963)
noticed that after treatment of early gastrulae with 10 jug/ml of actinomycin for 2-3 days, the resultant larvae had poorly developed axial
structures, but blood cells differentiated normally (cf. Brächet et al.,
1964).
A limited plasticity of the potentiality for synthesis of Hb is seen in
normal development, but some treatments resulting in partial or complete organization of a secondary embryo may induce other cells to
become mesodermal blood islands. Furthermore, the potency of mesoderm during its determination may be shifted, the so-called "dorsalization" phenomenon. When the medioventral section of the marginal zone
of early gastrulae is cultured in Holtfreter's solution, blood islands and
nephric tubules usually result. However, if the expiant is exposed to an
ammonia solution for a brief period, the expiant will form notochord
and somites, the frequency of formation of blood islands being reduced
(Yamada, 1961).
According to some authors, association with endoderm may also be
necessary for complete differentiations of erythrocytes. Brauns (1940)
surgically produced "endoderm free" embryos, and concluded that blood
cells could form in isolated mesoderm. They do not develop, however, to
the terminal stages characteristic of these early erythrocytes. He produced "bauschstuck" embryos by constriction and noted that virtually
107
Brauns (1940). The usual "defect" and "isolation" experiments were
carried out in all these studies, and the results showed quite clearly the
ventral mesoderm has assumed its potential erythropoietic function by
the neurula stage, determination probably taking place during gastrula
stages. Hb can be detected by benzidine staining at the tailbud stage
(Slonimski, 1931). Pantelouris et al (1963) injected females of Xenopus
with Fe
59
and studied the localization of Fe
59
in the oocytes and embryos
from the injected female. Fe
59
is diffusely distributed over the whole
embryo at the blastula stage, but a definite gradient appears in late
blastula and early gastrula embryos, with heavier labeling in the ventral
portions of the embryo, especially the endoderm and adjacent mesoderm.
This conforms to the embryological expectations. Brown and Caston
(1962) have isolated the iron storage protein, ferritin, from eggs of
Rana pipiens.
Throneberry and Shaver (1962) applied immunological methods to the
question of when Hb first forms in frog embryos. They report in their
abstract that they obtained specific antibodies against adult Hb. They
claim globin was found in extracts from all stages, even body cavity
eggs, but heme was not detectable until hatching.
The effect of agents affecting RNA metabolism on amphibian embryos
has been investigated. One such agent, actinomycin D, is very toxic, and
death, developmental arrest, and cytolysis ensue. Flickinger (1963)
noticed that after treatment of early gastrulae with 10 jug/ml of actinomycin for 2-3 days, the resultant larvae had poorly developed axial
structures, but blood cells differentiated normally (cf. Brächet et al.,
1964).
A limited plasticity of the potentiality for synthesis of Hb is seen in
normal development, but some treatments resulting in partial or complete organization of a secondary embryo may induce other cells to
become mesodermal blood islands. Furthermore, the potency of mesoderm during its determination may be shifted, the so-called "dorsalization" phenomenon. When the medioventral section of the marginal zone
of early gastrulae is cultured in Holtfreter's solution, blood islands and
nephric tubules usually result. However, if the expiant is exposed to an
ammonia solution for a brief period, the expiant will form notochord
and somites, the frequency of formation of blood islands being reduced
(Yamada, 1961).
According to some authors, association with endoderm may also be
necessary for complete differentiations of erythrocytes. Brauns (1940)
surgically produced "endoderm free" embryos, and concluded that blood
cells could form in isolated mesoderm. They do not develop, however, to
the terminal stages characteristic of these early erythrocytes. He produced "bauschstuck" embryos by constriction and noted that virtually