Human models for White Sutton syndrome: POGZ mutations change the transcriptome and induce defects in neural progenitor cell biology

Abstract

Intellectual disability (ID) and autism spectrum disorders (ASD) are complex neurodevelopmental conditions with high genetic heterogeneity. Studies indicate that 10%-40% of individuals with ID also have ASD, suggesting shared molecular mechanisms between these disorders. Recent next-generation sequencing studies have highlighted a significant role of de novo mutations in ASD, particularly those with large effects. Among these, POGZ (Pogo Transposable Element with zinc finger “ZNF” domain) has emerged as a frequently mutated gene with potential loss-of-function effects in ASD patients. However, the underlying molecular mechanisms and the pathogenic impact of POGZ mutations are not fully understood.

POGZ encodes a protein that is mainly binds to heterochromatin protein 1α and contributes to gene regulatory functions. Functionally, POGZ is critical for kinetochore assembly, sister chromatid cohesion, and mitotic chromosome segregation. POGZ deficiency can lead to premature mitotic exit, polyploidy, and potential cell death or genomic instability, which may disrupt neural development and brain function. POGZ thought to act as a transcriptional regulator, potentially influencing molecular networks that are critical for neuronal function.

This PhD study investigated the cellular and molecular mechanisms by which POGZ mutations contribute to neurodevelopmental disorders (NDDs) using human induced pluripotent stem cells (iPSCs) derived from patient and CRISPR/Cas9-mediated gene editing to introduce heterozygous POGZ mutations. These mutant iPSCs were differentiated into neural progenitor cells (NPCs) and neurons under both two-dimensional (2D) and three-dimensional (3D) culture conditions to analyze the effects of POGZ mutations on neural development.

Key findings of the study indicated that frameshift mutations in the N-terminus or the HP1-binding zinc finger-like (HPZ) domain of POGZ led to decreased POGZ protein expression without disrupting its nuclear localization. Using 3D neurospheres and brain organoids, it was found that POGZ-deficient cells exhibited impaired self-renewal of NPCs, alongside enhanced differentiation and increased neuronal migration. Additionally, analysis of the transcriptome via RNA sequencing revealed widespread changes in gene expression in NPCs carrying POGZ mutations. These alterations were significantly enriched for genes involved in mitotic chromatid segregation, DNA repair, nonsense-mediated decay, and alternative splicing. Notably, the data revealed a transcriptomic signature characterized by the elevated expression of neuron-specific genes, suggesting an "accelerated differentiation" phenotype in mutant NPCs, mirroring the behavior observed in the 3D neurosphere models.

Furthermore, CUT&Tag sequencing was employed to identify direct targets of POGZ, providing evidence that POGZ directly regulated genes linked to synaptic function, chromosome segregation, and Wnt signaling. The overrepresentation of autism-associated risk genes among POGZ-regulated targets further suggested a potential link between POGZ dysfunction and the etiology of NDDs, including ASD.

This analysis emphasized the critical role of POGZ in regulating neural development at both the cellular and molecular levels. Understanding how POGZ mutations drive alterations in NPC behavior and gene regulation, is crucial for developing targeted therapeutic strategies for conditions associated with POGZ dysfunction. Ultimately, this study aimed to bridge the gap between genetic findings and pathophysiological mechanisms in NDDs, providing deeper insights into the developmental disruptions caused by POGZ mutations.