Myoglobin synthesis of embryo and adult avian tissue studied immunologically

Relationship between the concentration of myoglobin and parvalbumin in various types of muscle tissues from chickens

The concentration of parvalbumin was determined in various types of chicken muscle by immunological analysis and was compared with that of myoglobin. Parvalbumin was present specifically in skeletal muscle and absent in cardiac and gizzard muscle; exceptionally, neither parvalbumin nor myoglobin was detected in white breast muscle. The wing and leg red muscles, which had larger amounts of myoglobin, contained smaller quantities of parvalbumin. In these muscles, the concentration of parvalbumin was inversely related to that of myoglobin (correlation coefficient = -0.69). Both myoglobin and parvalbumin were observed in the legs of 18-d-old embryos; the parvalbumin content exceeded that of myoglobin until the birds were 4 to 6 weeks old, but the relationship was reversed thereafter. Myoglobin in gizzard muscle was present in 18-d-old embryos and increased markedly at hatching; it was already present in cardiac muscle at an early embryonic stage, increasing gradually until 14 weeks after hatching.

The erythroid cells and haemoglobins of the chick embryo

The changes in the types of erythroid cells produced during embryogenesis of the chick have been correlated with the changes in the types of haemoglobins found in the embryo. Primitive erythroid cells constitute the only red blood cells of 2- to 5-day embryos. The first recognizable immature definitive erythroid cells appear in the embryonic circulation at 5 to 6 days and progressively replace the primitive cells, such that by 14 to 16 days the primitive cells constitute less than 1 % of the circulating erythroid cells. Primitive erythropoiesis is strikingly different from definitive erythropoiesis. At any one time point between 2 and 16 days, all of the isolated primitive cells appear, by morphological criteria, to be at the same stage of maturation, and, although variation in cell size is observed, for an individual maturation stage, the small cells are not more mature than the medium-size cells, nor are the large cells less mature than the medium or small cells. Maturing primitive erythroid cells undergo the progressive changes in cell structure characteristic of erythroid maturation in mammalian erythropoietic systems, but do so as a uniform cell population. Haemoglobin, isolated from primitive erythroid cells of 2- to 5-day embryos, shows two components on polyacrylamide gel electrophoresis, haemoglobin E and haemoglobin P. The haemoglobin E/P ratio is constant in lysates from 2- to 5-day embryos. A t 6 to 7 days when the first haemoglobinized immature definitive erythroid cells appear in the embryonic circulation, two new haemoglobin components are observed in lysates of erythroid cells. These two new haemoglobin components are electrophoretically and immunologically identical to the two haemoglobin components of adult chickens, haemoglobins A and D. As the definitive erythroid cells replace the primitive erythrocytes in the embryonic circulation, the haemoglobins A and D increase in amount and replace haemoglobin P. Haemoglobin P cannot be detected immunologically in erythroid cell lysates from 16-day embryos which contain less than 1 % primitive cells. In erythroid cell lysates from late embryos, which contained few, if any, primitive erythrocytes, a minor haemoglobin, electrophoretically similar to haemoglobin E on pH 10.3 polyacrylamide gels, is consistently observed. This component differs from haemoglobin E on pH 8.9 polyacrylmide gels, on Sephadex G-100 columns, on polyacrylamide gels of different porosities, and shows a reaction of only partial identity with haemoglobin E by two-dimensional immunodiffusion. This haemoglobin component, haemoglobin H, is detectable electrophoretically in lysates from 12-day embryos and immunologically in lysates from 8-day embryos. Haemoglobin H has not been observed in adult chickens. The switch from the production of primitive to definitive erythroid cells during development of the chick embryo is associated with the initiation of synthesis of three new haemoglobins, the two adult haemoglobins and haemoglobin H. The haemoglobin D /A ratio of adult chicken haemoglobin, determined from the ratio of gel scan peak masses, is 0.30. When haemoglobins D and A first appear in erythroid cell lysates from 6- to 7-day embryos, the haemoglobin D /A ratio is about 0.9. T he D/A ratio of lysates falls to 0.5 by 16 to 18 days, a time when 99 % of the erythroid cells of the embryo are mature definitive erythrocytes. However, the haemoglobin D /A ratio of lysates from late embryos and young chicks of 0.5 to 20 days of age is consistently greater than that of adult chicken haemoglobin. Definitive erythrocytes of chick embryos and young chicks appear to differ from definitive cells of adult chickens in at least two ways: the presence of haemoglobin H and the higher haemoglobin D/A ratio.