Tissue and site-specific methylation correlates with expression of the mouse lactoferrin gene

We have previously examined the regulatory region of the mouse lactoferrin gene and have identified sequences essential for basal and hormonally induc ed expression. In this study, we explore the relationship between the methy lation state of the mouse lactoferrin gene promoter and its expression in s elected mouse tissues. In a transient expression system, transcriptional ac tivity was blocked after in vitro methylation of the regulatory region of t he mouse lactoferrin gene. In addition, the in vivo methylation state of th ree promoter region sites was assessed using Southern blot analysis of DNA digested with methylation-insensitive and -sensitive restriction enzymes. T he results showed that site -455, upstream of the mouse lactoferrin estroge n response module, was highly unmethylated in DNA from both hormone-treated and -untreated mouse lung, liver, and spleen tissues. Also, in both treate d and untreated samples, the -54 site is uniquely highly unmethylated in li ver DNA, while the -22 site is unmethylated in spleen DNA. Northern blot an alysis showed lactoferrin expression in tissues that were unmethylated at a minimum of two sites. These results show that the alteration of the methyl ation status of the three sites are tissue-specific and are associated with constitutive expression of lactoferrin.