Altered Dendrites in YFP-MeCP2 Mutant Mice Figure 5. Developmental progression of cortical YFP expression. Left column: 200 mm coronal sections from YFP-H MeCP2J littermate pairs (, Bregma 0.14 mm in WT). The anterior commissure was used as a reference anatomical marker. Right column: maximum intensity projections of confocal fluorescence imaging z-stacks from cingulate cortex. The red box in P9 mutant (rotated 90u clockwise) corresponds to the region imaged in each brain. Single bright YFP+ L5 pyramidal neurons are observed in both genotypes as early as P9. By P12 YFP expression has been strongly upregulated in the WT, after which the number of YFP+ cells continues to increase more slowly until stabilizing to mature levels sometime between P21 and P40. The number of YFP+ cells in mutant males also continues to increase, but at a slower rate, and final levels remain below those seen in the WT. All confocal fluorescence images shown were obtained from the brain section shown except P9 WT, which was obtained from a tissue section 400 mm anterior due to sparse YFP labeling at this age. Left column scale bar = 0.5 mm. Right column scale bar = 100 mm. doi:10.1371/journal.pone.0031896.g005 The varied and contradictory nature of these results may be a direct consequence of the intrinsically disordered structure of MeCP2, which confers autonomous functionality to several biochemical domains that may act alone or in concert [55]. The pairing of a highly flexible tertiary structure with independently operating functional domains presents an attractive explanation for the multifunctional nature of MeCP2 as well as the diversity of mutant phenotypes. In conjunction with physiological and transcriptional profiling, direct morphological comparison be- tween cellular subpopulations, both within and across mutant mouse lines, may present a valuable tool for dissociating how each MeCP2 domain contributes to the generation or maintenance of cellular character in the CNS. Interaction of Mecp2 Mutation with the Thy-1-YFP Transgene We analyzed the effects of a specific Mecp2 mutation on a fluorescently labeled population of cortical neurons. Similar strategies using Thy-1-YFP/-GFP mice have been been employed elsewhere in studies of Mecp2 and other transgenes (e.g. [32,56– 60]). The principal utility of this approach arises from the use of cell type-specific promoters to restrict analysis to defined cellular subtypes. Given the increasingly evident taxonomic diversity of neuronal subpopulations based on clustered patterns of hodology, morphology, gene expression, and electrophysiological properties [61–63], this type of approach is most salient when evaluating gene mutations with highly context-dependent effects. PLoS ONE | www.plosone.org 7 March 2012 | Volume 7 | Issue 3 | e31896