Alpha-globin Gene Cluster Research Articles

Thalassaemia intermedia in Cyprus: the interaction of alpha and beta thalassaemia.

Restriction endonuclease analysis has been performed on the alpha and beta globin gene clusters of 57 Cypriots homozygous for beta thalassaemia, 30 with the transfusion dependent form of the condition (thalassaemia major) and 27 who are less severely affected (thalassaemia intermedia). There was a significant difference in the incidence of alpha thalassaemia between the two groups: 14/27 of the patients with thalassaemia intermedia also had deletion forms of alpha thalassaemia, while only 4/30 of the patients with thalassaemia major were similarly affected. Thus in Cypriot patients who are homozygous for beta thalassaemia the co-inheritance of alpha thalassaemia is an important factor in determining the clinical course.

DNA methylation in chicken alpha-globin gene expression.

We have investigated certain specific methylation sites of the chicken alpha-globin gene cluster in DNA from embryonic and adult erythroid cells as well as from brain and sperm cells. Eight contiguous DNA fragments of the alpha-globin gene cluster were subcloned from a recombinant lambda phage. The subclones were used as probes to map all the Msp I/Hpa II and Hha I sites in the unmethylated cloned DNA and specific sites of methylation in and around the alpha-globin gene cluster in chromosomal DNA. The data show that sperm DNA is totally methylated at these restriction sites in the globin gene region, as is brain DNA, with some exceptions. Interestingly, the methylation status of specific sites 5' to the coding sequences is correlated with expression of the embryonic or adult alpha-globin genes in different stages of erythroid development. Some sites showing partial methylation, however, do not conform to the model that transcribed genes are unmethylated or undermethylated. We also find a well-defined 3.5-kilobase region of DNA 5' to the alpha-globin gene cluster in which all C-C-G-G sites are resistant to Msp I digestion in all tissues. This "Msp block" is presumably caused by 5-MeCpC methylation.

Hemoglobin H disease and mental retardation: a new syndrome or a remarkable coincidence?

Each of three families of northern European origin contains a mentally retarded son with hemoglobin H (Hb H) disease. One parent is a carrier of mild alpha-thalassemia and the other is normal, suggesting that this form of Hb H disease results from the interaction between an inherited defect of alpha-chain production and one member of the pair in chromosome 16 and a new mutation on the other. Restriction-enzyme analysis indicated that the new mutation was not the same in the other three patients, and demonstrated at least two hitherto undescribed lesions involving the alpha-globin gene cluster. Unless the association between the Hb H disease and mental retardation is fortuitous, the new mutations may also be related to the development changes in these children. Since the mutations only came to light because there was concurrent inheritance of an additional alpha-thalassemia determinant, this type of mutation of chromosome 16 may have been overlooked in other mentally retarded patients.

Localization of a unique gene by direct hybridization in situ.

Previous determination of the chromosomal location of unique genes have required that the chromosomes of interest be fractionated, either by species-specific chromosome loss from interspecies hybrids, or by physical fractionation procedures. We have developed a general technique for the localization of a unique gene, which requires no prior chromosome fractionation. The technique involves the use of a labeled hybrid cDNA plasmid for direct hybridization in situ to metaphase cells from the organism under investigation. As a model system for development of this technique, we have employed a human alpha-globin cDNA plasmid (JW101) to localize the corresponding gene cluster. To obtain a sufficiently large autoradiographic signal, we have both labeled this plasmid with 125I to a high specific activity (10(9) dpm/micrograms) and taken advantage of the ability of a double-stranded probe to form networks. To obtain sufficient hybridization specificity, various experimental procedures were used, the most important of which was the choice from among a range of probe concentrations of the highest that does not yield excessive background hybridization. We have shown that, with an autoradiographic exposure time of only 12 days, use of this technique correctly localized the human alpha-globin gene cluster to chromosome 16. This technique should be generally applicable to the localization of any gene for which a corresponding cDNA hybrid plasmid is available.