Pogz Mutation Leads to Abnormal Behavior and Transcription Dysregulation in the Brain
De-novo loss-of-function mutations in POGZ (Pogo Transposable Element with ZNF domain) were identified in multiple individuals with developmental delay, half of them with a diagnosis of autism spectrum disorder (ASD). POGZ consistently interacts with the three isotypes of HP1 and therefore may play a key role in transcription regulation. As of today, the molecular, cellular and neuronal mechanisms through which POGZ is associated with ASD remain incompletely understood.
Our overall aim was to delineate the function of POGZ in the normal brain and in ASD. In particular, we inquired how rare genetic insults in this gene influence networks of genes leading to ASD.
Our approach to study the function of POGZ was based on Pogz-deficient mice. We used a conventional knockout mice with a whole body heterozygous mutation in Pogz gene (Pogz KO+/-), and conditional knockout mice that harbor a homozygous Pogz knockout restricted to the brain (Pogz cKO-/-). To characterize the anatomical and behavioural phenotypes we used several staining methods and a battery of behavioural assays relevant to ASD. To explore how POGZ modulates gene expression in the brain and identify its transcriptional targets we used RNA-Seq and dual-luciferase reporter assay.
Pogz deficient mice showed a significant growth delay relative to their WT littermates. Behaviourally, these mice exhibited reduced anxiety, deficits in learning and memory and impaired sociability. Similar to what was reported in humans, the KO mice were “overly friendly”. To identify defects in neural development that may explain the behavioral phenotypes, we first studied brain anatomy, including the structure of the cortex, but found that Pogz-deficient mice displayed no detectable defects. However, adult neurogenesis was significantly decreased in the hippocampus because of reduced neuronal survival. Gene expression profiling of the hippocampus identified a large number of dysregulated genes. The majority of differentially expressed genes with fold change above 1.5 or above 2 were upregulated (67%, P = 0.026; 93%, P = 0.00098, respectively) and enriched for genes involved in axon guidance, and regulation of locomotion. Since POGZ was found to be an integral part of the HP1 protein complexes, and given the gene expression results, we hypothesized that POGZ plays a key role in transcription repression. Indeed, dual-luciferase reporter assay showed that POGZ acts as a negative regulator of transcription through its interaction with HP1 proteins.
Our study shows that Pogz deficiency in mice is sufficient to cause ASD-related behaviours, similar to those found in human individuals with de-novo mutations in POGZ. The behavioral abnormalities and growth delay may result from lower survival of newly born neurons and transcriptional dysregulation in mature neurons caused by POGZ deficiency.