MeCP2 mutant protein is expressed in astrocytes as well as in neurons and localizes in the nucleus.

The MECP2 gene, located at Xq28, encodes methyl-CpG-binding protein 2 (MeCP2), which is frequently mutated (up to 90%) in Rett syndrome (RTT). RTT is a progressive neurodevelopmental disorder, which affects primarily girls during early childhood and it is one of the most common causes of mental retardation in females. R270X is one of the most frequent recurrent MECP2 mutations among RTT cohorts. The R270X mutation resides within the TRD-NLS (Transcription Repression Domain-Nuclear Localization Signal) region of MeCP2 and causes a more severe clinical phenotype with increased mortality as compared to other mutations. To evaluate the functional role of the R270X mutation, we generated a transgenic mouse model expressing MeCP2(270_EGFP) (human mutation equivalent) by BAC recombineering. The expression pattern of MeCP2(270_EGFP) was similar to that of endogenous MeCP2. Strikingly, MeCP2(270_EGFP) localizes in the nucleus, contrary to the conjecture that R270X could cause disruption of the NLS. In primary hippocampal cells, we show that MeCP2(270_EGFP) was expressed in astrocytes by colocalization with the astrocyte-specific marker glial fibrillary acidic protein. Our data showing expression of MeCP2(270_EGFP) in transgenic mice astrocytes further reinforce the recent findings concerning the expression of MeCP2 in the glial cells.