FIGURE 13.

Proposed model for cell non-autonomous effects of balanced and skewed XCI ratios. (A) Cell- autonomous effects on the morphology of MeCP2- containing neurons, including reductions in dendritic length and fewer branch points compared to MeCP2+ cells, may render them less competitive for synaptic connections in the heterozygous brain. (B) A balanced XCI ratio may provide MeCP2- neurons more opportunity to make connections, as there are fewer large MeCP2+ neurons to compete with. This may reduce the severity of the morphological phenotype of MeCP2- cells. (C) A skewed XCI ratio favoring MeCP2+ neurons provides for a more competitive environment for synaptic connections. MeCP2- neurons are less able to compete and therefore have a more severe morphological phenotype.