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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.


Related in: MedlinePlus

Age, phenotype severity and XCI ratios are not correlated in Mecp2+/- mice. Increasing age is not a predictor of phenotype severity of Mecp2+/- mice. Aged Mecp2+/- animals are not more likely to have highly skewed XCI ratios (10–30% mutant neurons, red circles) and XCI ratios do not predict phenotype severity at any age. Premature death (x’s) occurred across both young and old age groups. A premature death is defined as any animal that died spontaneously (not sacrificed for experiments), therefore XCI ratios were unavailable.
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Figure 8: Age, phenotype severity and XCI ratios are not correlated in Mecp2+/- mice. Increasing age is not a predictor of phenotype severity of Mecp2+/- mice. Aged Mecp2+/- animals are not more likely to have highly skewed XCI ratios (10–30% mutant neurons, red circles) and XCI ratios do not predict phenotype severity at any age. Premature death (x’s) occurred across both young and old age groups. A premature death is defined as any animal that died spontaneously (not sacrificed for experiments), therefore XCI ratios were unavailable.

Mentions: To determine the interaction between age, cell phenotype, and XCI ratios, animals were scored for their phenotype severity at their time of sacrifice for immunohistochemical staining (from 5 to 22 months of age). Within the cohort of mice selected for our study the phenotype severity was highly variable, with some mice dying prematurely as young as 2 months of age (i.e., before they could be used for experiments), and others surviving into old age (22 months) with only mild symptoms (Figure 8). Increasing age did not correlate with increased phenotype severity (p = 0.2, R2 = 0.038). To determine whether symptom levels vary according to XCI ratio, XCI ratios were analyzed by immunohistochemistry and compared against phenotype severity. It was found that XCI ratios were also not correlated with phenotype severity (Figure 8; p = 0.66, R2 = 0.0062). Surprisingly, mice with a highly skewed XCI ratio favoring expression of the wild-type chromosome (10% MeCP2-:90% MeCP2+) did not have less severe symptoms than mice with a more balanced XCI ratio (50% MeCP2-:50% MeCP2+).


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)

Age, phenotype severity and XCI ratios are not correlated in Mecp2+/- mice. Increasing age is not a predictor of phenotype severity of Mecp2+/- mice. Aged Mecp2+/- animals are not more likely to have highly skewed XCI ratios (10–30% mutant neurons, red circles) and XCI ratios do not predict phenotype severity at any age. Premature death (x’s) occurred across both young and old age groups. A premature death is defined as any animal that died spontaneously (not sacrificed for experiments), therefore XCI ratios were unavailable.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: Age, phenotype severity and XCI ratios are not correlated in Mecp2+/- mice. Increasing age is not a predictor of phenotype severity of Mecp2+/- mice. Aged Mecp2+/- animals are not more likely to have highly skewed XCI ratios (10–30% mutant neurons, red circles) and XCI ratios do not predict phenotype severity at any age. Premature death (x’s) occurred across both young and old age groups. A premature death is defined as any animal that died spontaneously (not sacrificed for experiments), therefore XCI ratios were unavailable.
Mentions: To determine the interaction between age, cell phenotype, and XCI ratios, animals were scored for their phenotype severity at their time of sacrifice for immunohistochemical staining (from 5 to 22 months of age). Within the cohort of mice selected for our study the phenotype severity was highly variable, with some mice dying prematurely as young as 2 months of age (i.e., before they could be used for experiments), and others surviving into old age (22 months) with only mild symptoms (Figure 8). Increasing age did not correlate with increased phenotype severity (p = 0.2, R2 = 0.038). To determine whether symptom levels vary according to XCI ratio, XCI ratios were analyzed by immunohistochemistry and compared against phenotype severity. It was found that XCI ratios were also not correlated with phenotype severity (Figure 8; p = 0.66, R2 = 0.0062). Surprisingly, mice with a highly skewed XCI ratio favoring expression of the wild-type chromosome (10% MeCP2-:90% MeCP2+) did not have less severe symptoms than mice with a more balanced XCI ratio (50% MeCP2-:50% MeCP2+).

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