The Methyl-CpG-Binding Protein 2 (Mecp2) Splice Variants Become Differentially Distributed During Postnatal Brain Development
J.M.Dragich; Y.H.Kim; A.P.Arnold; N.C.Schanen.
Abstract
Mutations in MECP2 are the primary cause of Rett Syndrome, an X-linked neurological disorder associated with postnatal disruption of CNS maturation. The MECP2 gene undergoes alternative splicing, generating transcripts encoding proteins that vary in the N-termini. We examined the distribution of two Mecp2 splice variants in the postnatal mouse brain by in situ hybridization with riboprobes directed against sequences within exons 3-4 present in both the Mecp2e1 and Mecp2e2 transcripts (total Mecp2) or with a riboprobe against exon 2, which will only recognize Mecp2e2. These studies revealed regional and age-related differences in transcript abundance. In newborn mice (P1), signals for both probes were widely distributed, with largely overlapping expression patterns throughout the brain. However in juvenile (P21) and adult (P60) mice, expression of the Mecp2e2 splice variant became restricted predominately to nuclei within the dorsal thalamus (DT) and cortical layer V. In contrast, the total Mecp2 riboprobe only weakly labeled the DT and cortical layer V in P21 and P60 animals, while it heavily labeled surrounding brain regions. To quantify differences in transcript levels, nuclei within the DT or hypothalamus were dissected out of coronal sections from P60 mice. Quantitative real-time PCR results confirm that Mecp2e2 is significantly more abundant in the DT than the hypothalamus and that the inverse is true for the Mecp2e1 transcript. To examine the temporal regulation of Mecp2e2 expression in the DT, we examined additional time points between the ages of P1 and P20 and found that as early as P9, Mecp2e2 is preferentially found in the DT and cortical layer V. The differential distribution of Mecp2e1 and Mecp2e2 suggests that there is a postnatal regulation of Mecp2 splicing that is brain region specific.
Lay Summary
In 2004, a previously unknown form of MeCP2 was described. However, how, when and where this new form differs from the originally described form of MeCP2 in its distribution in the brain remains unknown. In this abstract, the authors describe their analysis of the developmental pattern of expression of this new form of MeCP2, in the developing mouse brain.