Yamaguchi M and Wakahara M (2001), Contribution of ventral and dorsal mesoderm to ...

XB-ART-9662

Dev Biol 2001 Feb 15;2302:204-16. doi: 10.1006/dbio.2000.0122.

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Contribution of ventral and dorsal mesoderm to primitive and definitive erythropoiesis in the salamander Hynobius retardatus.

Yamaguchi M , Wakahara M .

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Previously, we found that the conversion of hemoglobins (Hbs) from the larval to the adult type occurred within a single erythroid cell population in a salamander, Hynobius retardatus ("Hb switching" model), whereas the transition involves replacement of red-blood-cell (RBC) populations ("RBC replacement" model) in many amphibians (M. Yamaguchi, H. Takahashi, and M. Wakahara, 2000, Dev. Gene Evol. 210, 180-189). To further characterize the Hb transition, developmental changes in the erythropoietic sites have been intensively analyzed using larval- and adult-specific globin antibodies and globin and GATA-3 RNA probes. Cells of the ventral blood island (VBI) and the dorsolateral plate (DLP) in embryos differentiate in situ to erythroid cells that contain larval globin mRNA, suggesting that both the VBI and the DLP contribute to "primitive" erythropoiesis. In contrast, the expression pattern of the GATA-3 gene suggests that cells of the DLP may contribute to "definitive" hematopoiesis. In order to determine whether it is possible to define a definitive erythropoiesis in H. retardatus or not, further experiments were done: (1) when metamorphosing larvae were treated with phenylhydrazine to induce anemia and then bled at the postmetamorphic stage after recovery from the anemia, a precocious Hb transition was observed in these animals; (2) an RBC population expressing only adult Hb was confirmed by subtracting the number of RBCs expressing larval Hb from the total number of RBCs during metamorphosis. All these results support the existence of a definitive erythroid cell population that contributes only adult RBCs in this species.

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Species referenced: Xenopus
Genes referenced: gata3

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FIG. 4. (A) Nucleotide and deduced amino acid sequences of Hynobius GATA-3 cDNA clone. The 2260-bp insert includes DNA-binding zinc-finger region (underlined). Since the insert lacks a poly(A) tail, it may lack the 39 terminal sequences to some extent. Stop codon is shown by an asterisk. (B) Deduced amino acid sequences of the zinc-finger region in Hynobius GATA-3 are compared with those of mouse, chick, Xenopus, and zebrafish. These sequences are highly conserved, and the similarity of the Hynobius GATA-3 zinc-finger region to those of other species is about 90%. Asterisks indicate common amino acid residues among 5 vertebrate species.

FIG. 11. Tentative model showing the hematopoietic sites that contribute to primitive and definitive erythropoiesis and the cellular mechanism of Hb transition from the larval to the adult type in H. retardatus compared with a bony fish (zebrafish) and an anuran amphibian (Xenopus laevis). The sites from which primitive blood arises are shown by red, and those from which definitive blood arises are shown by blue. In the zebrafish embryo, the intraembryonic ICM is a source of primitive blood, and the cells of the posterior ICM may contribute to definitive hematopoiesis. On the other hand, primitive erythropoiesis in X. laevis occurs in the VBI, and the DLP (intraembryonic) cells remain undifferentiated until later for definitive hematopoiesis. The H. retardatus embryo also has two distinct hematopoietic sites, the VBI and DLP. The DLP cells of H. retardatus, however, differentiate in situ to RBCs containing larval globin. Occurring much earlier than morphological metamorphosis, the Hb transition initiates within a single erythroid-cell population, depending on pituitary factor(s). During metamorphosis, RBCs of another lineage from the DLP, which come to express only adult Hb, begin to proliferate and differentiate in response to thyroid hormones. Pink triangles indicate larval Hb and orange squares indicate adult Hb.