The control of haemoglobin synthesis

Humoral regulation of hemoglobin transition from larval to adult types in a salamander, Hynobius retardatus

In amphibians hemoglobin (Hb) transition from larval to adult types occurs during metamorphosis. Hemoglobin transition in the salamander Hynobius retardatus also occurs during metamorphosis, but depends on activity of the pituitary gland, rather than that of the thyroid gland. These findings were supported by the fact that the transplanted pituitary gland to hypophysectomized (Hx) larvae exerted accelerating effects on Hb transition. Contrary to this, a homogenate of the pituitary gland from Xenopus laevis had no accelerating effect on Hb transition when injected into Hx larvae of H. retardatus. Whereas exogeneously applied triiodothyronine (T3) or a combination of T3 and hydrocortisone had an accelerating effect on Hb transition in the Hx larvae, a single treatment with hydrocortisone in the Hx larvae had no effect. When an inhibitor of synthesis of adrenocortico-steroid hormones, metyrapone, was applied in combination with goitrogens to intact larvae, Hb transition from larval to adult types was suppressed compared with normal controls, suggesting that the thyroid-corticoid system is involved in Hb transition. These results suggest that Hb transition in H. retardatus is controlled by two independent accelerating factors, from both the pituitary gland and the thyroid-corticoid system. These control mechanisms are different from the general regulation of metamorphosis that occurs in many amphibians. A tentative model of hormonal controls in Hb transition from larval to adult types during the metamorphosis in H. retardatus is presented.

Heterochrony and neotenic salamanders: possible clues for understanding the animal development and evolution

A synthesis of developmental genetics with evolutionary genetics is now making possible to understand significant evolutionary changes in multicellular organisms. The key concept for unifying the two must be heterochrony. Heterochrony causes evolutionary modifications due to changes in timing and/or rate of development. The heterochrony is conventionally categorized into three patterns as neoteny (retardation in somatic development), progenesis (acceleration in gonadal development), and direct development (acceleration in somatic development, resulting in lack of larval or tadpole stages). A lot of species showing neoteny are known in urodeles, but not in anurans. Neotenic urodeles are also divided into three categories; permanent or obligate, "inducible" obligate and facultative neotenies. Hynobius retardatus, a specific population of which had been reported to show neoteny but is believed to be extinct at present, has become to be used for experimental analysis of heterochronic expression of several adult characters during its ontogeny. Gonadal maturation and a transition of globin subunits from larval to adult types have been shown to occur independently on the morphological metamorphosis in H. retardatus. Mechanisms underlying the heterochrony, including morphogenetic clock, heterochronic genes in Drosophila and C. elegans, temporal colinearity in Hox gene complex in mice, and atavistic transformation induced by altered expression of Hox genes are discussed in terms of current molecular biology.

GATA factors and the origins of adult and embryonic blood in Xenopus: responses to retinoic acid

The transcription factors, GATA-1, -2 and -3 play essential roles in the differentiation of haematopoietic cells. To study the process of blood formation during vertebrate development we have used the expression of these GATA factors to locate haematopoietic cells in Xenopus embryos and to act as sensors for the effects of all-trans retinoic acid (RA), a signalling molecule which influences both anteroposterior patterning and haematopoietic differentiation. GATA factor expression was detected in the leading edge of the gastrulating mesoderm, in the ventral blood island (VBI) and dorsolateral plate (DLP) mesoderms and in a population of cells between the VBI and DLP. The VBI contributes to both embryonic and adult blood, whereas the DLP contains precursors of adult blood only, which have not been identified previously with molecular markers. The possibility that the GATA-2-expressing cells between the VBI and DLP were haematopoietic progenitors migrating from the VBI to the DLP was ruled out by transplantation analysis. Differential effects of RA on the expression of GATA-1 and GATA-2 suggest that RA has a direct action on haematopoietic differentiation, rather than on the formation of haematopoietic mesoderm.

Some functional and structural properties of Bufus paracnemis and Pipa pipae hemoglobins

1. Hemoglobin from terrestrial and an aquatic amphibia Bufo paracnemis and Pipa pipae respectively both living in the same region (Belém, Pará) were compared. 2. The number of hemolysate components were determined by starch-gel electrophoresis and CMC-chromatography. P. pipae hemoglobin presented 4 components and B. paracnemis 2, all of anodic mobility. 3. Functional properties of the hemoglobins (oxygen affinity. Bohr effect, carbon monoxide equilibrium) were determined and compared. 4. The differences found in the functional properties were correlated with the different habitat: aquatic or terrestrial for the amphibia. 5. The study of the oxygen functional properties of the hemoglobin showed in the stripped proteins of P. pipae in the presence of ATP, an oxygen affinity (P50 = 7.24 mmHg) that of B. paracnemis at the same pH (P50 = 15.84 mmHg). At high pH the P50 values are different being 15.84 mmHg for the terrestrial frog and 5 mmHg for P. pipae haemoglobin both at pH 8. In addition Bohr effect was noted only in P. pipae hemolysate in the presence of ATP. 6. The CO-equilibrium affinity constant in the presence of ATP are similar in both frogs, of about, log C50 = -6.9. The ratio Pco/Po2 for B. paracnemis hemoglobin was about 300 whereas for that of P. pipae was about 100 only. 7. The kinetic study of reactive sulfhydryl groups in both frog hemoglobin with 4-PDS (specific SH group reagent was used and shown high pseudo-first order constant for B. paracnemis hemoglobin) (k' = 0.46/min) either in presence or not of ATP, compared for that of P. pipae where values were K' = 0.003/min in the stripped protein and k' = 0.014/min in the presence of ATP. 8. Denaturation kinetic studies of the hemoglobin with sodium benzoate was performed and the results were compared with that of Rana catesbeiana, i.e. the pseudo-first order of the hemoglobin denaturation reaction are low for the aquatic P. pipae adult although for the B. paracnemis high molecular resistant was also noted. For P. pipae hemoglobin, nevertheless with ATP such resistance becomes higher. This does not occur with B. paracnemis hemoglobins.

Molecular cloning of cDNA sequences coding for the major alpha- and beta-globin polypeptides of adult Xenopus laevis

This report describes the synthesis and cloning of almost complete DNA copies of the mRNAs encoding the major alpha-globin and major beta-globin of X. laevis. Double-stranded globin cDNA was inserted into the PstI site of the plasmid pBR322 and two cloned recombinants (designated pXG6C1 and pXG8D2) were selected. These were shown to contain almost complete copies of X. laevis globin mRNA. Restriction enzyme maps were determined for each cDNA sequence using the established method of partial digestion of end labelled DNA. However, this procedure was modified such that isolation of individual DNA fragments was no longer required. Each plasmid was shown, by both hybrid arrested translation and filter selection of complementary RNA, to contain a sequence coding for one or other of the two major globin polypeptides. Sufficient DNA sequence information has been determined from each cDNA clone to demonstrate that pXG8D2 contains a beta-globin sequence and pXG6C1 contains an alpha-globin sequence.

Synthesis of erythrocyte-specific proteins in cultured friend leukemia cells

We have studied synthesis of specific proteins in two permanent lines of Friend virus-induced erythroleukemia cells (Friend line 745 and Ostertag line FSD-1, both derived from DBA/2 mice). By 96 hr following treatment with 1-2% dimethyl sulfoxide (Me2SO), up to 25% of the protein being synthesized by both these cultures is hemoglobin. At that time, hemoglobin constitutes up to 10% of the cellular soluble protein. Both lines synthesize heme and globin coordinately, and alpha and beta globin chains in a nearly balanced 1:1 ratio. However, the ratio of betaMajor:betaMinor chains synthesized by these induced Friend leukemia (FL) cells is approximately 9 in the FSD-1 line and 1.3 in the Friend Clone 745 line, whereas it is 4 in normal adult DBA/2 mouse erythrocytes. Evidence for the latter conclusion was obtained by electrophoresis of FL hemoglobins on cellulose acetate membranes, and also by chromatographic separation of alpha, betaMajor, and betaMinor globins on carboxymethylcellulose in 8 M urea at 20 degrees C. Carbonic anhydrase activity per mg protein is 3 times higher in induced than in control cultures. 2,3-diphosphoglyceric acid is not found in induced FL cells. Induced and control FL cells agglutinate strongly and equally with Phaseolus vulgaris phytohemagglutinin. The developmental process in these cultured leukemia cells appears to be an aberrant erythropoiesis.