Developmental Regulation of Hypomethylation of δ-Crystallin Genes in Chicken Embryo Lens Cells

Abstract

Sequences in the two δ-crystallin genes become hypomethylated when they are expressed in the chick lens. This system is particularly advantageous for studying temporal changes in hypomethylation, since lens tissue can be isolated at all developmental stages. In previous work we have shown that most HpaII sites become hypomethylated within the δ1-crystallin gene long after δ-crystallin gene activation. One site is hypomethylated when crystallin mRNA begins to be synthesized at high levels at 50 h; we show here that this site maps to the 3′ end (intron 15) of the δ1-crystallin gene. In addition, we have examined the methylation status of HpaII and HhaI sites found near the 5′ end of the δ1-crystallin gene. Two HhaI sites adjacent to a viral core enhancer sequence in intron 2 are also first hypomethylated at 50 h. These findings point to regions of the δ1 gene that should be investigated further for functional significance in regulating δ-crystallin transcription.