The Thy-1 gene is expressed in a tissue- and stage-specific pattern and has a typical 1.6kb methylation-free island (MFI) covering about 600bp upstream and downstream of the two alternative first exons. By microinjection of a mouse Thy-1.1/human Thy-1 gene into fertilized eggs, we were able to show that the MFI is restored in the transgenic mice. The flanking sequence became methylated, but the MFI remains unmethylated in all tissues of transgenic mice at different developmental stages tested, irrespective of the site of expression of the gene. There is one exception, in extra-embryonal tissues of 14.5 day embryos a small percentage of the islands were methylated. We conclude that maintenance of the MFI is regulated by cis-acting sequences present within the gene, and indicates that the unmethylated state of the islands is consistent with a necessary but not sufficient condition for expression of the gene.

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Nucleic Acids Research
Erasmus MC: University Medical Center Rotterdam

Kolsto, A-B, Kollias, G, Giguere, V, Isobe, K-I, Prydz, H, & Grosveld, F.G. (1986). The maintenance of methylation-free islands in transgenic mice. Nucleic Acids Research, 14, 9667–9678. Retrieved from