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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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Diagram of average MeCP2 WT, MeCP2+, and MeCP2- layer V pyramidal neurons. The average MeCP2 WT and MeCP2+ neurons are equivalent across all morphological parameters investigated except soma and nuclear size. The average MeCP2- neuron (right) has approximately 15% less total dendritic length compared to either of the other genotypes. The average MeCP2- neuron has three fewer branch points, leading to a reduced number of higher order branches. The maximum branch order of MeCP2- neurons is also reduced. MeCP2- neurons have the same average maximum radial distance as both MeCP2 WT and MeCP2+ neurons. Somata of MeCP2- neurons are smaller than MeCP2+ especially in highly skewed XCI animals. Branch order: first = red, second = orange, third = green, fourth = blue, fifth = purple, sixth = black. Radii are 20 μm.
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Figure 12: Diagram of average MeCP2 WT, MeCP2+, and MeCP2- layer V pyramidal neurons. The average MeCP2 WT and MeCP2+ neurons are equivalent across all morphological parameters investigated except soma and nuclear size. The average MeCP2- neuron (right) has approximately 15% less total dendritic length compared to either of the other genotypes. The average MeCP2- neuron has three fewer branch points, leading to a reduced number of higher order branches. The maximum branch order of MeCP2- neurons is also reduced. MeCP2- neurons have the same average maximum radial distance as both MeCP2 WT and MeCP2+ neurons. Somata of MeCP2- neurons are smaller than MeCP2+ especially in highly skewed XCI animals. Branch order: first = red, second = orange, third = green, fourth = blue, fifth = purple, sixth = black. Radii are 20 μm.

Mentions: We find that MeCP2- layer V pyramidal neurons in heterozygous brains have shorter basal dendritic length, due to their having fewer third and fourth order branches compared to MeCP2+ neurons (see Figure 12 for summary). This supports previous research in Mecp2tm1.1Jae male mice that also found a reduction in the number of higher order branches in layer V cells (Stuss et al., 2012). Within the basal dendritic compartment, the principal difference between neurons containing mutant MeCP2 protein compared to those expressing the wild-type allele in both Mecp2+/- and Mecp2+/+ animals is a selective reduction in the number of third and fourth order branches. The similar pattern of reduced basal dendritic morphology of Layer V pyramidal neurons for both MeCP2- neurons in Mecp2+/- females and male Mecp2-/y mice indicates that MeCP2 acts predominantly in a cell-autonomous manner to affect the dendritic morphology of this compartment of MeCP2- neurons. These results are consistent with other studies that found that callosal projection neurons from Mecp2-/y mice transplanted into either wild-type or Mecp2-/y brains had primarily cell autonomous reductions in dendritic morphology (Kishi and Macklis, 2009).


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)

Diagram of average MeCP2 WT, MeCP2+, and MeCP2- layer V pyramidal neurons. The average MeCP2 WT and MeCP2+ neurons are equivalent across all morphological parameters investigated except soma and nuclear size. The average MeCP2- neuron (right) has approximately 15% less total dendritic length compared to either of the other genotypes. The average MeCP2- neuron has three fewer branch points, leading to a reduced number of higher order branches. The maximum branch order of MeCP2- neurons is also reduced. MeCP2- neurons have the same average maximum radial distance as both MeCP2 WT and MeCP2+ neurons. Somata of MeCP2- neurons are smaller than MeCP2+ especially in highly skewed XCI animals. Branch order: first = red, second = orange, third = green, fourth = blue, fifth = purple, sixth = black. Radii are 20 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 12: Diagram of average MeCP2 WT, MeCP2+, and MeCP2- layer V pyramidal neurons. The average MeCP2 WT and MeCP2+ neurons are equivalent across all morphological parameters investigated except soma and nuclear size. The average MeCP2- neuron (right) has approximately 15% less total dendritic length compared to either of the other genotypes. The average MeCP2- neuron has three fewer branch points, leading to a reduced number of higher order branches. The maximum branch order of MeCP2- neurons is also reduced. MeCP2- neurons have the same average maximum radial distance as both MeCP2 WT and MeCP2+ neurons. Somata of MeCP2- neurons are smaller than MeCP2+ especially in highly skewed XCI animals. Branch order: first = red, second = orange, third = green, fourth = blue, fifth = purple, sixth = black. Radii are 20 μm.
Mentions: We find that MeCP2- layer V pyramidal neurons in heterozygous brains have shorter basal dendritic length, due to their having fewer third and fourth order branches compared to MeCP2+ neurons (see Figure 12 for summary). This supports previous research in Mecp2tm1.1Jae male mice that also found a reduction in the number of higher order branches in layer V cells (Stuss et al., 2012). Within the basal dendritic compartment, the principal difference between neurons containing mutant MeCP2 protein compared to those expressing the wild-type allele in both Mecp2+/- and Mecp2+/+ animals is a selective reduction in the number of third and fourth order branches. The similar pattern of reduced basal dendritic morphology of Layer V pyramidal neurons for both MeCP2- neurons in Mecp2+/- females and male Mecp2-/y mice indicates that MeCP2 acts predominantly in a cell-autonomous manner to affect the dendritic morphology of this compartment of MeCP2- neurons. These results are consistent with other studies that found that callosal projection neurons from Mecp2-/y mice transplanted into either wild-type or Mecp2-/y brains had primarily cell autonomous reductions in dendritic morphology (Kishi and Macklis, 2009).

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