Characterization of two rat globin cDNA clones

Molecular cloning and characterization of two sets of alpha-theta genes in the rat alpha-like globin gene cluster

The highly heterogeneous rat hemoglobin system was investigated at the gene level. Two regions of the alpha-like globin gene cluster from a Wistar rat were isolated. Four lambda Dash recombinant clones carrying rat alpha-like globin genes were localized on two distinct gene regions. A region of approximately 16kb was found to contain the 5'-IIalpha1-psi theta 1-3' loci, and another of approximately 24kb the 5'-IIalpha2-psi theta2-psiI alpha3-3' loci. Both IIalpha1 and IIalpha2 are considered to be active, coding the IIalpha-globin chain. The nt sequences of IIalpha1 and IIalpha2 are identical except for six nt in the non-coding region. The psiI alpha3 locus is a truncated pseudogene. The putative promoter region of an alpha-like globin gene is joined directly to the third exon, homologous to that of Ialpha-globin cDNA. psi theta1 and psi theta2 are also pseudogenes, as evidenced by several deletions located in the protein-coding regions of these loci. The psi theta1 and psi theta2 loci exhibit extensive homology, but the restriction maps of these genes and their flanking regions differ considerably. Genomic Southern blot analyses of the total liver DNA from six rats showed the existence of three theta-globin-related genes, including psi theta1 and psi theta2. These results indicate that the two gene regions investigated are not allelic variants, but may be generated by block duplication. This is the first report of the existence of rodent theta-globin genes.

Molecular evidence for increased hematopoietic proliferation in the spleen of the b/b laboratory rat

The splenomegaly and the appearance of a significant number of CFU-E (erythroid colony-forming units) and BFU-E1 (erythroid burst-forming units) in the Belgrade laboratory rat (b/b) spleen prompted us to analyse further the molecular evidence for increased hematopoietic proliferation in the b/b spleen. Messenger RNAs (mRNAs) specific for globins, proteins for iron transport and deposition and the band 3 protein were used in rat erythropoietic tissues as markers for proliferation and erythroid differentiation. In the b/b spleen, all mRNAs analysed display an erythroid-specific pattern of expression. This analysis also revealed an enhanced level of mRNA for ferritin in the +/b spleen, whereas erythrocyte-specific mRNA production was normal.

Genomic organization and characterization of a three-gene rat adult beta-globin haplotype

The isolation and detailed characterization of a three-beta-globin gene (GloB) haplotype in the Sprague-Dawley (S-D) rat is described. An enriched library, lambda SDHelib, was screened with a human GloB probe, humbg44, and from which a beta minor gene, Rathbbz, was isolated, sequenced and characterized. A S-D rat GloB-specific probe, Ratbgze12, derived from the Rathbbz gene, was then used to screen a S-D rat genomic library, lambda SDglib. The clone T1510 was isolated and identified to include the entire Rathbbz gene and part of another GloB gene, Rathbby, which was 5' upstream from Rathbbz. Chromosomal walking upstream using the riboprobe, rnaT71, led to the isolation of an overlapping clone, Ta49, which was shown to include two full-length GloB genes; the most 5' was Rathbbx followed by Rathbby. Sequence data suggests that Rathbbx is a beta major gene, whereas Rathbby is a hybrid gene of Rathbbx and Rathbbz. Genomic hybridization confirmed this particular three-gene haplotype in the S-D rat. This haplotype, a1, may be the prototype of the GloB cluster in rat.

Variant chromosomal arrangement of adult beta-globin genes in rat

The genomic organization of three haplotypes of beta-globin genes was determined to resolve the question of the number of those genes in rat. Haplotype a, found in inbred strain DA, has three genes or pseudogenes, while haplotypes b, found in AO, Y5 and Wistar strains, and c, found in Wistar strain, have five genes or pseudogenes each. In haplotypes b and c, the first gene is of beta major type and the remaining four are of beta minor type. Partial sequencing of six out of 13 genes shows that duplications of beta minor genes are causing polymorphism in a number of genes. Also, in haplotype b two beta minor genes have a 6.5-kb intron 2, while in haplotype c only one beta minor gene contains such a large intron 2. The three structurally different haplotypes described are not interconvertible by single recombination events. The results indicate that the rat has the highest number of adult beta-globin genes found in mammals so far.

Molecular cloning and sequence analysis of two rat major globin cDNAs

Two cDNA clones for globins of the adult Wistar rat were isolated from a reticulocyte cDNA library and the nucleotide sequences of the inserts were determined. One clone contained a cDNA insert consisting of 556 bp and the other contained one of 577 bp, both covering the entire coding sequences for rat globins. Comparisons of their predicted amino acid sequences with known sequences of rat globins revealed that these cDNAs coded for a rat major alpha- and a major beta-globin, I alpha and II beta, respectively. The cause of diversity of rat globins was discussed in terms of the nucleotide sequences of cDNAs and known amino acid sequences of globins.