Alternative polyadenylation of MeCP2: Influence of cis-acting elements and trans-acting factors

The human MeCP2 gene encodes a ubiquitously expressed methyl CpG binding protein. Mutations in this gene cause a neurodevelopmental disorder called Rett Syndrome (RS). Mutations identified in the coding region of MeCP2 account for approximately 65% of all RS cases. However, 35% of all patients do not show mutations in the coding region of MeCP2, suggesting that mutations in non-coding regions likely exist that affect MeCP2 expression rather than protein function. The gene is unusual in that is has a >8.5 kb 3' untranslated region (3' UTR), and the size of the 3'UTR is differentially regulated in various tissues because of distinct polyadenylation signals. We have identified putative cis-acting auxiliary regulatory elements that play a role in alternative polyadenylation of MeCP2 using an in vivo polyadenylation reporter assay and in a luciferase assay. These cis-acting auxiliary elements are found both upstream and downstream of the core CPSF binding sites. Mutation of one of these cis-acting auxiliary elements, a G-rich element (GRS) significantly reduced MeCP2 polyadenylation efficiency in vivo. We further investigated what trans-acting factor(s) might be binding to this cis-acting element and found that hnRNP F protein binds specifically to the element. We next investigated the MeCP2 3' UTRs by performing quantitative real-time PCR; the data suggest that altered RNA stability is not a major factor in differential MeCP2 3' UTR usage. In sum, the mechanism(s) of regulated alternative 3'UTR usage of MeCP2 are complex, and insight into these mechanisms will aid our understanding of the factors that influence MeCP2 expression.