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Genotype-specific effects of Mecp2 loss-of-function on morphology of Layer V pyramidal neurons in heterozygous female Rett syndrome model mice.

Rietveld L, Stuss DP, McPhee D, Delaney KR - Front Cell Neurosci (2015)

Bottom Line: Comparing basal dendrite morphology, soma and nuclear size of MeCP2+ to MeCP2- neurons reveals a significant cell autonomous, genotype specific effect of Mecp2.These data reveal cell autonomous effects of Mecp2 mutation on dendritic morphology, but also suggest non-cell autonomous effects with respect to cell size.Unexpectedly the MeCP2- neurons were smallest in brains where the XCI ratio was highly skewed toward MeCP2+, i.e., wild-type.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Victoria Victoria, BC, Canada.

ABSTRACT
Rett syndrome (RTT) is a progressive neurological disorder primarily caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2). The heterozygous female brain consists of mosaic of neurons containing both wild-type MeCP2 (MeCP2+) and mutant MeCP2 (MeCP2-). Three-dimensional morphological analysis was performed on individually genotyped layer V pyramidal neurons in the primary motor cortex of heterozygous (Mecp2(+/-) ) and wild-type (Mecp2(+/+) ) female mice ( > 6 mo.) from the Mecp2(tm1.1Jae) line. Comparing basal dendrite morphology, soma and nuclear size of MeCP2+ to MeCP2- neurons reveals a significant cell autonomous, genotype specific effect of Mecp2. MeCP2- neurons have 15% less total basal dendritic length, predominantly in the region 70-130 μm from the cell body and on average three fewer branch points, specifically loss in the second and third branch orders. Soma and nuclear areas of neurons of mice were analyzed across a range of ages (5-21 mo.) and X-chromosome inactivation (XCI) ratios (12-56%). On average, MeCP2- somata and nuclei were 15 and 13% smaller than MeCP2+ neurons respectively. In most respects branching morphology of neurons in wild-type brains (MeCP2 WT) was not distinguishable from MeCP2+ but somata and nuclei of MeCP2 WT neurons were larger than those of MeCP2+ neurons. These data reveal cell autonomous effects of Mecp2 mutation on dendritic morphology, but also suggest non-cell autonomous effects with respect to cell size. MeCP2+ and MeCP2- neuron sizes were not correlated with age, but were correlated with XCI ratio. Unexpectedly the MeCP2- neurons were smallest in brains where the XCI ratio was highly skewed toward MeCP2+, i.e., wild-type. This raises the possibility of cell non-autonomous effects that act through mechanisms other than globally secreted factors; perhaps competition for synaptic connections influences cell size and morphology in the genotypically mosaic brain of RTT model mice.

No MeSH data available.


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Soma and nuclear size comparison between wild-type and heterozygous females. (A,C) MeCP2 WT Layer V neurons (wild-type) are larger than MeCP2+ neurons in heterozygous mice, which suggests a non-cell-autonomous effect of MeCP2 deficiency (MeCP2 WT, n = 10 animals; MeCP2+, n = 11; MeCP2-n = 11). (B,D) MeCP2+ and MeCP2- neuronal populations in heterozygous brains each have a smaller proportion of large cells than the population of MeCP2 WT cells. The MeCP2- cell population also has fewer large cells than the MeCP2+ population in heterozygous brains. (total cells assessed MeCP2 WT, n = 761 neurons; MeCP2+, n = 482; MeCP2-n = 502). *p < 0.05 and **p < 0.01.
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Figure 11: Soma and nuclear size comparison between wild-type and heterozygous females. (A,C) MeCP2 WT Layer V neurons (wild-type) are larger than MeCP2+ neurons in heterozygous mice, which suggests a non-cell-autonomous effect of MeCP2 deficiency (MeCP2 WT, n = 10 animals; MeCP2+, n = 11; MeCP2-n = 11). (B,D) MeCP2+ and MeCP2- neuronal populations in heterozygous brains each have a smaller proportion of large cells than the population of MeCP2 WT cells. The MeCP2- cell population also has fewer large cells than the MeCP2+ population in heterozygous brains. (total cells assessed MeCP2 WT, n = 761 neurons; MeCP2+, n = 482; MeCP2-n = 502). *p < 0.05 and **p < 0.01.

Mentions: For the study summarized in Figures 7, 9, and 10, we did not have a comparison group of wild-type littermates, so it was not possible to test whether, MeCP2+ neurons were comparable to MeCP2 WT neurons, with respect to soma and nuclear size. Since a number of sources of error can potentially affect cell size, such as variation in cell shrinkage during fixation, we analyzed an entirely new group of mice comprising heterozygous females and their wild-type female littermates. As expected, comparison of MeCP2+ to MeCP2- soma and nuclear sizes in this new cohort of animals revealed a difference for the group mean data [Figure 11; mean soma difference 8.8 μm2, p < 0.0020, n = 11 animals; mean nuclear difference 4.1 μm2, p < 0.005). Within animal paired sample comparisons were effective to increase statistical significance and within animal soma and nuclear sizes were strongly correlated between genotypes (MeCP2+ regressed against MeCP2-, R2 = 0.97, p < 0.0001, nuclear R2 = 0.90 p < 0.0001), indicating that inter-animal variability contributes a substantial amount of variance to the group means.


Genotype-specific effects of Mecp2 loss-of-function on morphology of Layer V pyramidal neurons in heterozygous female Rett syndrome model mice.

Rietveld L, Stuss DP, McPhee D, Delaney KR - Front Cell Neurosci (2015)

Soma and nuclear size comparison between wild-type and heterozygous females. (A,C) MeCP2 WT Layer V neurons (wild-type) are larger than MeCP2+ neurons in heterozygous mice, which suggests a non-cell-autonomous effect of MeCP2 deficiency (MeCP2 WT, n = 10 animals; MeCP2+, n = 11; MeCP2-n = 11). (B,D) MeCP2+ and MeCP2- neuronal populations in heterozygous brains each have a smaller proportion of large cells than the population of MeCP2 WT cells. The MeCP2- cell population also has fewer large cells than the MeCP2+ population in heterozygous brains. (total cells assessed MeCP2 WT, n = 761 neurons; MeCP2+, n = 482; MeCP2-n = 502). *p < 0.05 and **p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4403522&req=5

Figure 11: Soma and nuclear size comparison between wild-type and heterozygous females. (A,C) MeCP2 WT Layer V neurons (wild-type) are larger than MeCP2+ neurons in heterozygous mice, which suggests a non-cell-autonomous effect of MeCP2 deficiency (MeCP2 WT, n = 10 animals; MeCP2+, n = 11; MeCP2-n = 11). (B,D) MeCP2+ and MeCP2- neuronal populations in heterozygous brains each have a smaller proportion of large cells than the population of MeCP2 WT cells. The MeCP2- cell population also has fewer large cells than the MeCP2+ population in heterozygous brains. (total cells assessed MeCP2 WT, n = 761 neurons; MeCP2+, n = 482; MeCP2-n = 502). *p < 0.05 and **p < 0.01.
Mentions: For the study summarized in Figures 7, 9, and 10, we did not have a comparison group of wild-type littermates, so it was not possible to test whether, MeCP2+ neurons were comparable to MeCP2 WT neurons, with respect to soma and nuclear size. Since a number of sources of error can potentially affect cell size, such as variation in cell shrinkage during fixation, we analyzed an entirely new group of mice comprising heterozygous females and their wild-type female littermates. As expected, comparison of MeCP2+ to MeCP2- soma and nuclear sizes in this new cohort of animals revealed a difference for the group mean data [Figure 11; mean soma difference 8.8 μm2, p < 0.0020, n = 11 animals; mean nuclear difference 4.1 μm2, p < 0.005). Within animal paired sample comparisons were effective to increase statistical significance and within animal soma and nuclear sizes were strongly correlated between genotypes (MeCP2+ regressed against MeCP2-, R2 = 0.97, p < 0.0001, nuclear R2 = 0.90 p < 0.0001), indicating that inter-animal variability contributes a substantial amount of variance to the group means.

Bottom Line: Comparing basal dendrite morphology, soma and nuclear size of MeCP2+ to MeCP2- neurons reveals a significant cell autonomous, genotype specific effect of Mecp2.These data reveal cell autonomous effects of Mecp2 mutation on dendritic morphology, but also suggest non-cell autonomous effects with respect to cell size.Unexpectedly the MeCP2- neurons were smallest in brains where the XCI ratio was highly skewed toward MeCP2+, i.e., wild-type.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Victoria Victoria, BC, Canada.

ABSTRACT
Rett syndrome (RTT) is a progressive neurological disorder primarily caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2). The heterozygous female brain consists of mosaic of neurons containing both wild-type MeCP2 (MeCP2+) and mutant MeCP2 (MeCP2-). Three-dimensional morphological analysis was performed on individually genotyped layer V pyramidal neurons in the primary motor cortex of heterozygous (Mecp2(+/-) ) and wild-type (Mecp2(+/+) ) female mice ( > 6 mo.) from the Mecp2(tm1.1Jae) line. Comparing basal dendrite morphology, soma and nuclear size of MeCP2+ to MeCP2- neurons reveals a significant cell autonomous, genotype specific effect of Mecp2. MeCP2- neurons have 15% less total basal dendritic length, predominantly in the region 70-130 μm from the cell body and on average three fewer branch points, specifically loss in the second and third branch orders. Soma and nuclear areas of neurons of mice were analyzed across a range of ages (5-21 mo.) and X-chromosome inactivation (XCI) ratios (12-56%). On average, MeCP2- somata and nuclei were 15 and 13% smaller than MeCP2+ neurons respectively. In most respects branching morphology of neurons in wild-type brains (MeCP2 WT) was not distinguishable from MeCP2+ but somata and nuclei of MeCP2 WT neurons were larger than those of MeCP2+ neurons. These data reveal cell autonomous effects of Mecp2 mutation on dendritic morphology, but also suggest non-cell autonomous effects with respect to cell size. MeCP2+ and MeCP2- neuron sizes were not correlated with age, but were correlated with XCI ratio. Unexpectedly the MeCP2- neurons were smallest in brains where the XCI ratio was highly skewed toward MeCP2+, i.e., wild-type. This raises the possibility of cell non-autonomous effects that act through mechanisms other than globally secreted factors; perhaps competition for synaptic connections influences cell size and morphology in the genotypically mosaic brain of RTT model mice.

No MeSH data available.


Related in: MedlinePlus