Expression of MeCP2 in olfactory receptor neurons is developmentally regulated and occurs before synaptogenesis

Rett syndrome, a neurodevelopmental disorder hypothesized to be due to defective neuronal maturation, is a result of mutations in the mecp2 gene encoding the transcriptional repressor methyl-CpG binding protein (MeCP2). We utilized the olfactory system, which displays postnatal neurogenesis, as a model to investigate MeCP2 expression during development and after injury. MeCP2 expression increased postnatally, localizing to mature olfactory receptor neurons (ORNs) and sustentacular supporting cells. The timing of MeCP2 expression was defined by using detergent ablation (to remove the ORNs) and unilateral olfactory bulbectomy (to remove the ORN target), both of which increase neurogenesis. MeCP2 expression in the ORNs reached prelesioning levels as cells matured after ablation, whereas expression was not completely restored after bulbectomy, in which functional synaptogenesis cannot occur. Thus, MeCP2 expression correlates with the maturational state of ORNs, and precedes synaptogenesis. Identifying the time window of MeCP2 expression should help further clarify the biological defects in Rett syndrome.