Extensive methylation of a part of the CpG island located 3.0-4.5 kbp upstream to the chicken alpha-globin gene cluster may contribute to silencing the globin genes in non-erythroid cells

Here, we show that in the chicken genome, the domain of alpha-globin genes is preceded by a CpG island of which the downstream part (similar to 0.65 k bp) is heavily methylated in lymphoid cells; it is either non-methylated or undermethylated in erythroid cells. Recombinant plasmids were constructed with the corresponding DNA fragment (called "uCpG") placed upstream to a re porter CAT gene expressed from the promoter of the alpha(D) chicken globin gene. Selective methylation of CpG dinucleotides within the uCpG fragment s uppressed fivefold the expression of the CAT gene, when neither this gene i tself nor the alpha(D) promoter were methylated. Methylation of CpG dinucle otides within the aD gene promoter did not modify the suppression effect ex erted by methylated uCpG. We interpret these results within the frame of th e hypothesis postulating, that methylation of the upstream CpG island of th e chicken alpha-globin gene domain may play an essential role in silencing the alpha-globin genes in non-erythroid cells. (C) 2000 Academic Press.