106
FRED H. WILT
Moss and Ingram (1965) have recently investigated the mechanism
of the changes in Hb types in tadpoles of Rana catesbeiana. Cyanomethemoglobin and reduced, alkylated globin were fractionated by polyacrylamide-gel electrophoresis ; patterns of Hb synthesis were followed
by observing the labeling patterns after incubation of red cells in radioactive amino acids. Premetamorphic tadpoles (stage not specified) incorporate amino acids into the tadpole globin chains. If tadpoles are
treated with 5 X 10~
8 M thyroxine for 8 days, Hb synthesis is very low,
if present at all. However, after 15 days of treatment (hind leg to tail
ratio = 0.51) incorporation into Hb is again observed; on this latter
occasion the predominant incorporation is into the adult globin fractions
rather than the embryonic type. Thus, thyroxine sequentially represses
embryonic globin synthesis and subsequently stimulates adult globin
synthesis. Moss and Ingram propose that thyroxin acts on red cell
precursor populations, repressing production and release of "larval" cells
in the kidney, and later inducing division and subsequent release of
"adult" type cells from the spleen.
III. Embryology of Hemoglobin Formation
A. Amphibia
In this and the subsequent section, the main concern will be to describe
the hallmarks of the initial differentiation of erythrocytes, and some of
the possible tissue interactions and associations important for this development. The questions, some of which cannot be definitively answered,
center on the usual embryological concerns: when is Hb first synthesized,
where is it first synthesized, what kind of Hb is it, and what influences
do the tissue surroundings exert on its development.
Only the mesoderm can serve as a source of primary erythrocytes in
amphibia. The mechanisms of establishment of mesoderm are so well
known, and based on such extensive experimental investigation, that it
is not necessary to recount it here. The chapter by Holtfreter and
Hamburger in Analysis of Development (1955) presents a lucid summary
of this work. During normal embryogenesis the ventral mesoderm forms
a large blood island, which extends from the liver anläge to the tail at
the tailbud stages. Subsequently the blood island becomes a venous
lacuna with an endothelial hemopoietic wall. According to the histological
studies of Jordan and Speidel (1923), the kidney of Rana catesbeiana
assumes important hemopoietic functions in mature tadpoles, and during
metamorphosis the primary site of erythropoiesis shifts gradually to the
spleen. Bone marrow may be transitorily active in adults, especially in
the spring. The early embryology of the blood island has been studied
in detail by Federici (1926), Slonimski (1931), Yamada (1937), and
FRED H. WILT
Moss and Ingram (1965) have recently investigated the mechanism
of the changes in Hb types in tadpoles of Rana catesbeiana. Cyanomethemoglobin and reduced, alkylated globin were fractionated by polyacrylamide-gel electrophoresis ; patterns of Hb synthesis were followed
by observing the labeling patterns after incubation of red cells in radioactive amino acids. Premetamorphic tadpoles (stage not specified) incorporate amino acids into the tadpole globin chains. If tadpoles are
treated with 5 X 10~
8 M thyroxine for 8 days, Hb synthesis is very low,
if present at all. However, after 15 days of treatment (hind leg to tail
ratio = 0.51) incorporation into Hb is again observed; on this latter
occasion the predominant incorporation is into the adult globin fractions
rather than the embryonic type. Thus, thyroxine sequentially represses
embryonic globin synthesis and subsequently stimulates adult globin
synthesis. Moss and Ingram propose that thyroxin acts on red cell
precursor populations, repressing production and release of "larval" cells
in the kidney, and later inducing division and subsequent release of
"adult" type cells from the spleen.
III. Embryology of Hemoglobin Formation
A. Amphibia
In this and the subsequent section, the main concern will be to describe
the hallmarks of the initial differentiation of erythrocytes, and some of
the possible tissue interactions and associations important for this development. The questions, some of which cannot be definitively answered,
center on the usual embryological concerns: when is Hb first synthesized,
where is it first synthesized, what kind of Hb is it, and what influences
do the tissue surroundings exert on its development.
Only the mesoderm can serve as a source of primary erythrocytes in
amphibia. The mechanisms of establishment of mesoderm are so well
known, and based on such extensive experimental investigation, that it
is not necessary to recount it here. The chapter by Holtfreter and
Hamburger in Analysis of Development (1955) presents a lucid summary
of this work. During normal embryogenesis the ventral mesoderm forms
a large blood island, which extends from the liver anläge to the tail at
the tailbud stages. Subsequently the blood island becomes a venous
lacuna with an endothelial hemopoietic wall. According to the histological
studies of Jordan and Speidel (1923), the kidney of Rana catesbeiana
assumes important hemopoietic functions in mature tadpoles, and during
metamorphosis the primary site of erythropoiesis shifts gradually to the
spleen. Bone marrow may be transitorily active in adults, especially in
the spring. The early embryology of the blood island has been studied
in detail by Federici (1926), Slonimski (1931), Yamada (1937), and