Loss of X-linked Protocadherin-19 differentially affects the behavior of heterozygous female and hemizygous male mice

Abstract

Mutations in the X-linked gene Protocadherin-19 (Pcdh19) cause female-limited epilepsy and mental retardation in humans. Although Pcdh19 is known to be a homophilic cell-cell adhesion molecule, how its mutations bring about female-specific disorders remains elusive. Here, we report the effects of Pcdh19 knockout in mice on their development and behavior. Pcdh19 was expressed in various brain regions including the cerebral cortex and hippocampus. Although Pcdh19-positive cells were evenly distributed in layer V of wild-type cortices, their distribution became a mosaic in Pcdh19 heterozygous female cortices. In cortical and hippocampal neurons, Pcdh19 was localized along their dendrites, showing occasional accumulation on synapses. Pcdh19 mutants, however, displayed no detectable abnormalities in dendrite and spine morphology of layer V neurons. Nevertheless, Pcdh19 hemizygous males and heterozygous females showed impaired behaviors including activity defects under stress conditions. Notably, only heterozygous females exhibited decreased fear responses. In addition, Pcdh19 overexpression in wild-type cortices led to ectopic clustering of Pcdh19-positive neurons. These results suggest that Pcdh19 is required for behavioral control in mice, but its genetic loss differentially affects the male and female behavior, as seen in human, and they also support the hypothesis that the mosaic expression of Pcdh19 in brains perturbs neuronal interactions.

The Role of Protocadherin 19 (PCDH19) in Neurodevelopment and in the Pathophysiology of Early Infantile Epileptic Encephalopathy‐9 (EIEE9)

“…PCDH19 is thus able to enhance Rac1‐mediated WRC activation, which regulates actin cytoskeleton dynamics via the actin related protein 2/3 (Arp2/3) complex (Fig. D) (Hayashi et al , ; Nakao et al , ; Tai et al , ).…”

“…At the cellular level, PCDH19 expression has been reported in both glial cells (Zhang et al , ) and pyramidal neurons (Bassani et al , ; Hayashi et al , ). In the cortex, PCDH19 is expressed in neurons of the layers IV and V (Krishna et al , ; ; Pederick et al , ) and in the hippocampus it is expressed in both cornus ammonis (CA) regions and dentate gyrus (DG).…”

“…In particular, in the developing rat hippocampus, PCDH19 expression is the highest in CA1 and CA3 regions with respect to the DG, while it is the highest in the DG than other CA regions in adult brain (Gaitan and Bouchard, ; Hertel and Redies, ; Kim et al , ; ; Krishna‐K et al , ). In pyramidal neurons, PCDH19 has been detected along dendrites partially localizing with synapses (Bassani et al , ; Hayashi et al , ), supporting PCDH19 role in neuronal connectivity.…”

“…Despite all these evidences, PCDH19 role in neuronal morphology still needs in‐depth analysis and might be limited to some neuronal subtypes, since for instance, no morphological defects in dendrites and dendritic spines have been observed in neurons of the cortical layer V of Pcdh19 knock out mice (Hayashi et al , ).…”

A Rat Model of a Focal Mosaic Expression of PCDH19 Replicates Human Brain Developmental Abnormalities and Behaviors

“…Although these animal models are being instrumental and have started to shed light on the histopathology of the disease, they have mostly failed in fully recapitulating the EIEE9 phenotype regarding overt brain malformations together with significant behavioral deficits (Pederick et al 2016;Lotte et al 2016;Pederick et al 2018;Hayashi et al 2017;Lim et al 2019), which is a pre-requisite for future testing of potential therapeutic treatments. Moreover, while characterized by global mosaicism in all brain areas, the current models, although valuable, did not allow to dissect which particular affected brain area was responsible for the diverse behavioural phenotypes (Pederick et al 2016;Lotte et al 2016;Pederick et al 2018;Hayashi et al 2017;Lim et al 2019). Here, by using in utero electroporation as a technique to achieve a focal mosaic of Pcdh19 downregulated cells intermixed with wild type cells in the rat cortex or hippocampus, we mimicked the focal disorganization of the brain tissue described in EIEE9-affected people.…”