DNA methylation in chicken alpha-globin gene expression

Abstract

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.