Regulation of Onset of Rapid Hemoglobin Formation in Chick Blastodisc Blood Islands at the Transcription and Translation Levels. A Quantitative Analysis of Effects of Actinomycin, Ethanol, and Heme Precursors

Abstract

Amounts of hemoglobin formed by blastodiscs explanted for 24 h on minimal medium containing 2 μg/ml of actinomycin were independent of initial stage of development between the 2- and 6-somite stages. No additional hemoglobin was formed by 2- to 4-somite blastodiscs in response to further supplements of aminolevulinate. In contrast, levels of hemoglobin formed in the presence of actinomycin by both younger and older blastodiscs were dependent on initial stage of development, and also were enhanced by aminolevulinate. Protoporphyrin both stimulated formation of hemoglobin on minimal medium to levels comparable with those formed on egg homogenate medium, and prevented inhibition by actinomycin of the synthesis of macromolecules. Ethanol in concentrations up to 1% had no effect on levels of hemoglobin formed or incorporation of precursors into macromolecules.On egg homogenate medium low concentrations of ethanol markedly stimulated hemoglobin formation, probably in part through induced synthesis of aminolevulinate synthetase enzyme. High concentrations of ethanol also inhibited incorporation of leucine into polypeptide. Incorporation of uridine into polynucleotide was only partially inhibited on egg homogenate medium containing 2 μg/ml of actinomycin. Hemoglobin formation was markedly less inhibited than on minimal medium and was stimulated by both aminolevulinate and protoporphyrin.