The blood as an erythropoietic organ in anaemic Xenopus

Localization of hematopoietic cells in the bullfrog (Lithobates catesbeianus)

Amphibians represent the first phylogenetic group to possess hematopoietic bone marrow. However, adult amphibian hematopoiesis has only been described in a few species and with conflicting data. Bone marrow, kidney, spleen, liver, gut, stomach, lung, tegument, and heart were therefore collected from adult Lithobates catesbeianus and investigated by light microscopy and immunohistochemical methods under confocal laser microscopy. Our study demonstrated active hematopoiesis in the bone marrow of vertebrae, femur, and fingers and in the kidney, but no hematopoietic activity inside other organs including the spleen and liver. Blood cells were identified as a heterogeneous cell population constituted by heterophils, basophils, eosinophils, monocytes, erythrocytic cells, lymphocytes, and their precursors. Cellular islets of the thrombocytic lineage occurred near sinusoids of the bone marrow. Antibodies against CD34, CD117, stem cell antigen, erythropoietin receptor, and the receptor for granulocyte colony-stimulating factor identified some cell populations, and some circulating immature cells were seen in the bloodstream. Thus, on the basis of these phylogenetic features, we propose that L. catesbeianus can be used as an important model for hematopoietic studies, since this anuran exhibits hematopoiesis characteristics both of lower vertebrates (renal hematopoiesis) and of higher vertebrates (bone marrow hematopoiesis).

Changes in heat shock protein synthesis and hsp70 gene transcription during erythropoiesis of Xenopus laevis

As erythroid cells of Xenopus laevis differentiate, their capacity for transcription and protein synthesis becomes progressively restricted. Mature erythrocytes are thought to be transcriptionally inert and have very low levels of protein synthesis (Maclean et al., 1973, Cell Differ. 2, 261-269). We have examined actual and potential synthetic activity during erythropoiesis by comparing the patterns of protein synthesis and measuring the transcriptional activity of selected genes under ambient and heat shock conditions. As erythropoiesis proceeds, there is a progressive decrease in the number of heat shock proteins (hsps) whose synthesis is induced at elevated temperatures. Despite this repression, mature erythrocytes are able to respond to heat shock with the induction of synthesis of one protein, hsp70. In addition, an hsp70-like protein is synthesized constitutively in orthochromatic erythroblasts, the final erythroid cell stage before maturation into erythrocytes. An in vitro nuclear run-off transcription assay was used to study transcription of the hsp70, beta-globin, and ribosomal genes during erythropoiesis. beta-Globin and ribosomal gene transcription were detected at all stages of erythropoiesis, including the erythrocyte stage. However, transcription of the beta-globin gene relative to ribosomal gene transcription declines substantially in erythrocytes as compared to earlier stages. Hsp70 gene transcription shows both stage-specific and heat shock-dependent transcription. Orthochromatic erythroblasts and erythrocytes have heat shock-dependent hsp70 gene transcription, whereas the gene is transcribed at the earlier erythroblast stages at ambient temperature as well as during heat shock. The constitutive hsp70 transcripts made during these earlier stages may be stored for utilization in constitutive synthesis of the hsp70-like protein in orthochromatic erythroblasts. These data indicate that although erythrocytes become synthetically repressed during differentiation, they are less inert than previously thought. The data also reveal that the synthesis of hsps and related proteins is subject to both transcriptional and post-transcriptional control during erythropoiesis.

Ultrastructural studies on the thymus gland after the administration of phenylhydrazine to bank voles (Clethrionomys glareolus)

The thymus glands of wild and laboratory reared bank voles (Clethrionomys glareolus) were examined for ultrastructural changes before and after the administration of low (20 mg/kg) and high (60 mg/kg) doses of phenylhydrazine (PhZ) given intraperitoneally on days 0, 1 and 3 of a dosing regime. Erythrocytes developed in focal aggregations in the subcapsular and outer cortical zones. There was a marked depletion of the subcapsular cortex following drug treatment that was reversed with time. A large number of granulocytes were visible in the cortex after PhZ, and mast cells developed in situ.

Studies of the development of frog hemopoietic tissue in vitro. I. Spleen culture assay of an erythropoietic factor in anemic frog blood

A new in vitro technique has been described for demonstrating the presence of an erythropoietic factor in the circulating blood of frogs. The assay system consisted of MC33 medium, erythropoietically active spleen cells from Rana pipiens, and plasma or serum from frogs made anemic via phenylhydrazine or bleeding. The spleen cells, which remain erythropoietically active for up to nine days, were found to incorporate 59Fe, [3H]thymidine, [3H]uridine, and [3H]leucine at a greater rate in the presence of plasma or serum from anemic versus normal frogs. The hormones triiodothyronine, prolactin, and erythropoietin were not effective in eliciting an hemopoietic response. The data presented suggest that the spleen from that adult frog is a major site of erythroid differentiation and maturation.

In vitro culture of larval amphibian erythroblasts

A larval erythroblast culture method is described. By this method, it is possible to cultivate for several weeks a homogeneous population of cells (5-10(5) cells/ml medium on average after 4 or 5 days of culture), which are relatively synchronous with regard to their state of differentiation.