Age- and sex-related analysis of methylation of 5′-upstream sequences of Fmr-1 gene in mouse brain and modulation by sex steroid hormones
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Fmr-1 gene is implicated in synaptic plasticity and thereby learning, memory and cognition, and methylation of Fmr-1 gene is necessary for memory development that is an age-dependent phenomenon. Aging in general has been reported to affect methylation of gene, however, nothing is known on the age dependent variation in methylation of Fmr-1 gene. Using the brain tissues from male and female mice of various age groups and sex steroid hormones (testosterone or 17β-estradiol) as modulators, restriction enzymes Hpa II and Msp I and Southern blotting technique, we studied methylation of 5′-upstream sequences of Fmr-1 gene. Our data reveal that the methylation of the 5′-upstream sequences that include CpG islands in promoter and 5′-untraslated region (5′-UTR) gradually increases due to advancing age in both the sexes. 17β-estradiol lowers the methylation significantly in the brain of mouse of both male and female mouse in age-dependent manner where as testosterone does not affect it appreciably. The alteration in the methylation may be attributed to altered DNA methyl transferase (DNMT) activity as the age increases from young to old, and the 17β-estradiol may down regulate the DNMT activity in both the age and sex groups whereas the testosterone may not have similar effect on DNMT. Down regulation of methylation of Fmr-1 CpG island and/or 5′-UTR by 17β-estradiol might lead to derepression of Fmr-1 gene especially in old age. This finding on Fmr-1 methylation is novel and it might have implications in understanding fragile X related disorders and age-dependent alteration in LTP and LTD.
KeywordsAging Brain Aging DNA methylation Fmr-1 promoter Sex steroid hormones
The authors acknowledge Prof. B Oostra for providing plasmid pE5.1, Profs M.S. Kanungo and M.K. Thakur, India for extending support. KS acknowledges Junior and Senior research fellowship from the UGC, Govt. of India-sponsored CAS Program in Zoology.
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