Molecular aspects of embryonic mouse haemoglobin ontogeny

Abstract

Embryos from C57BL/6J mice between the gestational ages of 9 and 16 days possess three embryonic haemoglobins EI, EII and EIII, the proportions of which change as a function of gestational age. Component EIj originally present at approx. 65% at day 9, decreases to approx. 20% by day 16 We now report on studies of the developmental pattern of embryonic haemoglobin production in a pure strain of mice (C57BL/6J). The component haemoglobins have been isolated and quantified during early development. An analysis of the 02-binding parameters for each of the isolated components has allowed us to simulate mathematically the anomalous 02-binding curves of the whole-blood system in terms of the contributions of each of the embryonic components. The properties of the individual components and their relative contributions to the whole embryonic erythrocyte system have been rationalized on the basis of the changing physiological demands for°2 encountered by the embryo in its changing intra-uterine environment. Materials and methodsMice of the strain C57BL/6J were obtained from the Animal Laboratory of the Cancer Society of New Zealand and housed under normal conditions. Timed matings were secured by the usual methods (Whitten, 1958). Pregnant female mice were killed and embryos dissected in cold saline solution (0.9% NaCl) as quickly as possible. For embryos of gestational age greater than 11 days it was possible to separate the umbilical blood vessels from the placenta and obtain blood by capillary sampling. Where appropriate, the erythrocytes were separated Vol. 215

Stopped-flow kinetics of oxygen uptake and release by embryonic red blood cells

“…At 12 days' gestation, the embryonic red blood cells contain approx. 30 0 El, 45 % ElI and 25 0 EIII (Purdie et al, 1983). However, the Bohr effect and co-operativity of ElI and EIII are similar to that seen for adult mouse haemoglobin (Purdie et al, 1983).…”

“…30 0 El, 45 % ElI and 25 0 EIII (Purdie et al, 1983). However, the Bohr effect and co-operativity of ElI and EIII are similar to that seen for adult mouse haemoglobin (Purdie et al, 1983). The high 02 affinity of El coupled with its much lower 02 dissociation rate (Brittain et al, 1986) means that its effects are only expected to become significant in the latest stages of 02 release.…”

“…Mice of the strain C57 BL/6J were time-mated according to the usual methods (Whitten, 1958;Purdie et al, 1983), and pregnant females were killed at 12 days' gestation. Embryos were dissected into heparinized cold saline (0.9 % NaCl).…”

“…It was found to be necessary to modify the chemical reaction terms in eqns. (1) and (2) to take account of the shape of the complex binding curves obtained for the embryonic cells (Purdie et al, 1983;Brittain & Wells, 1982;Brittain, 1987) together with the measured Bohr effect (Fig. 2).…”

“…However, this model has not previously been developed to describe ligand-exchange processes in any other than biconcave disc-shaped erythrocytes. As part of an ongoing series of studies on the functional characteristics of embryonic haemoglobins (Brittain & Wells, 1982;Purdie et al, 1983;Brittain et al, 1986;Brittain, 1987) we have employed the experimental approaches of Vandergriff (1984) in order to study the 02 uptake and release processes in the embryonic red blood cells of mice at the polychromatophilic pre-erythrocyte stage of development. We report here these experimental findings, together with a modification to the original three-dimensional disc model ofVandergriff (1984) which allows us to accurately simulate these ligand exchange processes in the large, nucleated, pseudo-spherical embryonic red blood cells.…”