Science | Mosaic Expression in Synapses: Revealing the Molecular Mechanism of X-Linked PCDH19 Mutation Disease

Authoredited in NovemberMutations in the X chromosome-linked gene PCDH19 (Protocadherin-19) can cause epilepsy associated with PCDH19 disease.

PCDH19 disorders are usually accompanied by cognitive impairment, and 70% of patients have intellectual deficits [1].

Generally speaking, due to X-linked recessive inheritance, X-linked diseases show a more severe phenotype in males.

But on the contrary, the disorder caused by the PCHD19 mutation will show the characteristics of the disease in heterozygous females, while there are no obvious symptoms in hemizygous males.

Why this unusual situation occurred is still unknown.

In order to solve the mystery of this problem, the Hisashi Umemori research group of Harvard Medical School in the United States published a research paper in Science, entitled Female-specific synaptic dysfunction and cognitive impairment in a mouse model of PCDH19 disorder, which revealed that the PCHD19 mutation is in heterozygotes.
The specific molecular mechanism that shows the characteristics of cognitive impairment and other diseases in females but not males.

Regarding the characteristic that the disorder caused by the PCHD19 mutation has different performance in females and males, some studies have speculated that it may be due to heterozygous female cells expressing both wild-type cells and mutant PCDH19 cells, due to the X chromosome Random inactivation, so it may be due to the chimeric expression of PCDH19 causing pathogenic symptoms [2].

The PCHD19 gene encodes a single-pass transmembrane protein, which belongs to the pro-cadherin family.

PCDH19 mediates calcium-dependent cell-cell adhesion through the affinity binding of the extracellular cadherin domain.

Most disease-related mutations in the PCHD19 gene destroy the extracellular domain of PCDH19.

In order to analyze the function of PCDH19 in the brain, the authors used CRISPR-Cas9 gene editing technology to inactivate Pcdh19.

At the same time, in order to analyze the expression of PCDH19, the authors constructed an antibody against PCDH19.

Through PCDH19 antibody staining, the authors found that it was mainly expressed in the brain of mice (Figure 1).

In the hippocampus, the mossy fiber pathway is rich in PCDH19 protein.

PCDH19 is expressed in presynaptic and postsynaptic neurons of mossy fiber synapses.

Furthermore, by immunostaining cell markers in mossy fibers, the authors confirmed that PCDH19 expression is indeed located in mossy fiber synapses.

Figure 1 The structure diagram of PCDH19 and its expression characteristics in different tissues of mice.
Further, the authors hope to detect the phenotype of Pcdh19 mutant mice.

The authors found that the abnormal accumulation of Pcdh19+ and Pcdh19- cortical neurons in Pcdh19 mutant female mice is consistent with previous studies [3].

But the authors found that the mutation did not affect the length of mossy fiber axons, nor did it affect the strength of the underlying moss fiber.

However, the authors found that the ability of neurotransmitter release in Pcdh19 mutant female mice was significantly reduced, but this phenomenon was not observed in Pcdh19 mutant male mice.

Therefore, Pcdh19 mutant female mice will have specific synaptic function and plasticity impairment.

Moreover, the authors found that this specific damage can trigger cognitive dysfunction in Pcdh19 mutant female mice.

So, what is the molecular mechanism of specific mossy fiber synaptic dysfunction and cognitive impairment in Pcdh19 mutant female mice? Since the male hemizygous did not show mossy fiber synaptic dysfunction, the lack of homogenous interaction between PCDH19 alone cannot explain this defect.

For this reason, the authors hope to find other factors that interact with PCDH19.

Therefore, the authors focused on the study of the interaction between PCDH19 and N-cadherin, which is another cell adhesion molecule located at synapses [4].

To test this hypothesis, the authors first tested the interaction between PCDH19 and cadherin.

The authors found that there is indeed an interaction between PCDH19 and cadherin in the hippocampus.

But does the complex formed by PCDH19 and N-cadherin maintain the normal function of synapses in mossy fibers? The authors established a human embryonic kidney cell HEK cell and neuron co-culture system, which can express synapse-related factors through HEK cells to induce presynaptic differentiation of contact axons.

PCDH19 is not endogenously expressed in HEK cells, only N-cadherin is expressed.

In HEK cells, the authors overexpressed PCDH19 and N-cadherin at the same time or only expressed N-cadherin.
In this case, an experimental system was constructed in which PCDH19 and N-cadherin matched or mismatched (Figure 2).

This result confirms that the mismatch between PCDH19 and N-cadherin does damage the presynaptic development process (Figure 2).

Moreover, the mismatch between PCDH19 and N-cadherin mainly affects the density and size of β-catenin spots in Pcdh19 mutant female mice, thereby significantly affecting the function of mossy fiber synapses.

Figure 2 Using HEK cells and neuronal cells to detect the mismatch between PCDH19 and N-cadherin.
In general, this work found that presynaptic dysfunction of mossy fibers appeared in Pcdh19 mutant female mice but not Pcdh19 mutant male mice And cognitive deficits are mainly due to the mismatch between PCDH19 and N-cadherin, which damages the N-cadherin-dependent signaling pathway and damages the presynaptic development process (Figure 3).

Wild-type Pcdh19 and Pcdh19 mutant male mice were retained due to their interaction with PCDH19 or N-cadherin (Figure 3).

The research not only revealed the unique female-specific disease mechanism, but also proposed possible strategies based on this molecular interaction to treat the disease.

Figure 3 Working model (from the current review article Mosaic synapses in epilepsy) Original link: https://doi.
org/10.
1126/science.
aaz3893 Platemaker: Eleven References 1 Dibbens, LM et al.
X-linked protocadherin 19 mutations cause female-limited epilepsy and cognitive impairment.
Nature genetics 40, 776-781, doi:10.
1038/ng.
149 (2008).
2 Depienne, C.
et al.
Sporadic infantile epileptic encephalopathy caused by mutations in PCDH19 resembles Dravet syndrome but mainly affects females.
PLoS genetics 5, e1000381, doi:10.
1371/journal.
pgen.
1000381 (2009).
3 Pederick, DT et al.
Abnormal Cell Sorting Underlies the Unique X-Linked Inheritance of PCDH19 Epilepsy.
Neuron 97, 59-66.
e55, doi:10.
1016/j.
neuron.
2017.
12.
005 (2018).
4 Tai, CY, Kim, SA & Schuman, EM Cadherins and synaptic plasticity.
Current opinion in cell biology 20, 567-575, doi:10.
1016/j .
ceb.
2008.
06.
003 (2008).
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