Schematics of the Methyl CpG binding protein 2 gene ( Mecp2 ), Mecp2e1 / e2 transcripts, and known regulatory elements (REs). (A) Generation of MeCP2 isoforms by alternative splicing; mature Mecp2e1 transcripts comprise of exons 1, 3, and 4. Mature Mecp2e2 transcripts comprise of exons 2, 3, and 4 (adapted from [4, 11]). Exons are denoted as Ex. (B) Regulatory elements of the MECP2/Mecp2 gene. The MECP2/Mecp2 gene is reported to be regulated by negative and positive REs within the promoter and a silencer element within the intron 1 (information extracted from [12, 13]). For our studies we selected a 500-bp region in the promoter upstream of the exon 1 and a 1-kb region in the intron 1 upstream of the exon 2. Each sequence was divided into three regions, R1 to R3 in the Mecp2 promoter and R4 to R6 in the intron 1. Note that there are no CpG dinucleotides in the mouse genomic sequence between R5 and R6.