Regulation of Expression within a Gene Family

• Published in: The Journal of biological chemistry 1998-07, Vol.273 (27), p.17206-17215
• Main Authors: Klok, Erik Jan, van Genesen, Siebe T., Civil, Azem, Schoenmakers, John G.G., Lubsen, Nicolette H.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.27.17206

The six closely related and clustered rat γ-crystallin genes, the γA- to γF-crystallin genes, are simultaneously activated in the embryonic lens but differentially shut down during postnatal development with the γB-crystallin gene, the last one to be active. We show here that developmental silencing of the γD-crystallin promoter correlates with delayed demethylation during lens fiber cell differentiation. Methylation silencing of the γD-crystallin promoter is a general effect and does not require the methylation of a specific CpG, nor does methylation interfere with factor binding to the proximal activator. In later development, the γD-crystallin promoter is also shut down earlier by a repressor that footprints to the −91/−78 region. A factor with identical properties is present in brain. Hence, a ubiquitous factor has been recruited as a developmental regulator by the lens. All γ-crystallin promoters tested contain upstream silencers, but at least the γB-crystallin silencer is distinct from the γD-crystallin silencer. The γ-crystallin promoters were found to share a proximal activator (the γ-box; around −50), which behaves as a MARE. The γB-box is recognized with much lower avidity than the γD-box. By swapping elements between the γB- and the γD-crystallin promoter, we show that activation by the γB-box requires a directly adjacent −46/−38 AP-1 consensus site. These experiments also uncovered another positive element in the γD-crystallin promoter, around −10. In the context of the γD-crystallin promoter, this element is redundant; in the context of the γB-crystallin promoter, it can replace the −46/−38 element.