Presence of globin gene transcripts in chicken oocytes and of a partially processed globin RNA in early embryos

RNA isolated from chicken oocytes and early embryos of various stages of development were probed with cloned cDNA of the alpha type (pi, alpha D and alpha A) and beta type (beta A, globin genes. Transcripts of all genes were present, although at a very low level, in the RNA of oocytes, and of embryos of the blastula and gastrula stages, prior to the onset of globin synthesis at about 30 h incubation. Interestingly, Northern blotting of electrophoretically fractionated embryonic RNA made it possible to observe, at all stages of development and for all genes tested, RNA molecules several hundred nucleotides longer than mature mRNA. PCR amplification of the pi globin transcripts indicates that these additional sequences are localized upstream of the CAP site. These higher-MW forms were found to be replaced by normal-size globin mRNA several hours after the onset of globin synthesis. The relevance of these data to comprehension of how globin gene expression is controlled during development is discussed.