Unusual structure of the chicken embryonic alpha-globin gene, pi'.

Abstract

We report the DNA sequence of the globin locus encoding the chicken embryonic a-globin, i. The structure differs significantly from that of the two chicken adult a-globin genes, aA and aD, as well as from that of previously studied adult a-globin genes in that the introns of the m-" gene are substantially larger than those in adult a-globin loci. In contrast, the i' introns are structurally similar to the only other expressed embryonic a-globin gene reported to date, the human 'gene. While completing the sequence of the l' gene, we determined that only one chromosomal locus within the chicken genome hybridizes to a i' central exon probe. These data lead to the conclusion that if the equimolar chicken embryonic a-globin polypeptides, called wfand i', are indeed independently transcribed, then that transcription occurs from alleles of the same gene; however, we favor the possibility that the w gene does not actually exist. This conclusion is drawn from the observation that the two chromosomal alleles of embryonic a-globins (represented by recombinant bacteriophage ACaG5 and ACaG7) both encode i'.The a-and f3-globin genes of the chicken make up a small multigene family that is subject to temporal regulation of gene expression during development (switching). This regulation can be defined as occurring both within a single cell type (e.g., transient pH expression in the definitive erythroid cell) and in differentially related cell types [e.g., p versus /3 expression during the switch from embryonic globin synthesis in primitive erythroid cells to adult globin synthesis in definitive erythroid cells (1)]. To study the expression of those genes that are regulated during avian embryogenesis, we have isolated and characterized both a-and /3-globin linkage groups on recombinant bacteriophage (2-5).In this paper, we report the complete DNA sequence for the member of the globin gene family of the chicken that had not heretofore conclusively been identified in chromosomal DNA, that encoding the embryonic chicken a-globin. The gene sequence here reported encodes 7r', one of two major a-globins expressed exclusively in the primitive erythroid line. These two globins are reported to differ one from another by a single amino acid at position 124 of the polypeptide chain, being either alanine (vr) or glutamate (ir') (6).We (2) has been described (4,5). The position of the ir or r' gene within these recombinants was determined by positive blot hybridization with a radioactive cDNA probe prepared from globin mRNA isolated from embryos 4.5 days after fertilization, and lack of hybridization to the same restriction fragments with an adult globin-specific cDNA probe (ref. 4; data not shown). The chromosomal a-globin domain as defined by these hybridizations is shown by Fig. 1A, and, in particular, the locus reported herein is shown in Fig. 1B. Subelones prepared from this segment of the chromosome and containing the embryonic aglobin locus are shown in Fig. 1C, and sequence analysis strategy for the locus is shown in Fig. 1D....

Replacement variant histone genes contain intervening sequences.

“…The extreme difference in H3.3A and H3.3B intron sizes is interesting, however, since intron size is relatively well conserved in both introns among the embryonic alpha-, adult alpha-, and beta-globin subfamilies and for one of the two globin introns (the 5' one) among all but the embryonic alpha-globin genes of vertebrates (ca. 500 million years [10,11,13]). …”

Primitive and definitive erythropoiesis in the yolk sac: a birds eye view

“…Since the first report of partial beta globin peptide sequences from normal and sickle human blood cells (Ingram, 1956), efforts were made throughout the sixties and seventies to understand developmental changes in chicken hemoglobin heterogeneity at the protein level (Beaupain et al, 1979;Brown and Ingram, 1974;Bruns and Ingram, 1973;Fraser, 1961;Hashimoto and Wilt, 1966;Manwell et al, 1966;Manwell et al, 1963;Saha, 1964;Saha and Ghosh, 1965;Shimizu, 1972;Simons, 1966;van der Helm and Huisman, 1958;Wilt, 1962;Wilt, 1967). This was followed by the elucidation of chicken hemoglobin genes and genomic organization in the early eighties Dodgson et al, 1981;Dodgson et al, 1979;Dolan et al, 1983;Dolan et al, 1981;Engel and Dodgson, 1980;Engel et al, 1983;Reitman et al, 1993;Villeponteau et al, 1982;Villeponteau and Martinson, 1981) and of developmental changes in hemoglobin transcript profiles in the ninties (Mason et al, 1995;Minie et al, 1992). These studies, together with more recent genomic analysis, can be summarized as follows.…”

Excision close to matrix attachment regions of the entire chicken alpha-globin gene domain by nuclease S1 and characterization of the framing structures.

“…This domain represents one of the best studied genomic areas in higher eukaryotes in terms of the arrangement of up to 35 kb of DNA elements involved in chromatin structure, mechanisms of transcription, and control of gene expression. From a DNase I-hypersensitive site 14.5 kb upstream of the ir-,aD-, and aA-globin genes (8, 9) to a hypersensitive site 3 kb downstream of the gene cluster, multiple DNA elements such as matrix attachment regions (MARs) (8, 10, 11), topoisomerase II sites (6,8,12), a replication origin (13), enhancers (14-18), and a silencer (17) all thought to represent putative control elements, have been identified, in addition to the promoters of the individual genes (19,20) and repetitive DNA sequences (21). This region seems to be transcribed into a full-domain transcript which spans the entire domain between the most distal DNase I-hypersensitive sites (8,22,23), running right through all the DNA in the area between the external MARs, and also through an internal MAR placed upstream of the first gene.…”