Loss of MeCP2 causes subtle alteration in dendritic arborization of retinal ganglion cells

Methyl-CpG-binding protein (MeCP2) is highly expressed in neurons. It plays an important role in the development of synapses and the formation of circuits in the central nervous system (CNS). Mutations in MECP2 cause neurodevelopmental disorders and mental retardation in humans. Therefore, it has become important to determine the distribution and function of MeCP2 in vivo. The retina consists of three nuclear cell layers and two layers of synapses; neurons in each layer are connected to form fine circuits necessary for visual signal transduction. Using immunohistochemical analysis, we found that MeCP2 was expressed in all nuclear cell layers, with differences in the levels of MeCP2 expression observed among the layers. To understand the structural defects in the retina due to the loss of MeCP2, we sought to elucidate the organization of the retinal structure in the Mecp2 knockout (KO) mouse. Overall, we found a normal retinal structure in Mecp2 KO mice. However, because Mecp2 mutations have a highly variable effect on neuronal architecture, we analyzed morphological changes in a subset of retinal ganglion cells of Mecp2 KO mice. In Thy1-GFP mice crossed with Mecp2 mutant mice, Sholl intersections analyses showed a subtle increase in number of intersections due to increased branching proximal to the soma in Mecp2 KO mice. Our results demonstrate that the expression of MeCP2 and the effects of Mecp2 mutations are highly specific to tissue and cell types.