Biology subjects

Lizarraga, S. B.

Publications and source records attributed to Lizarraga, S. B..

5 recordsLinked to original sources

bioRxiv2025

Mutations in ASH1L cause a neurodevelopmental disorder with sex differences in epilepsy and autism

To understand brain phenotypes associated with ASH1L, we performed both studies in mouse models and clinical phenotyping of human subjects. We found in mice that ASH1L mutations result in seizures, microcephaly, and also less complex dendritic morphology. When we analyzed human subjects based for epilepsy, intellectual disability, and ASD, we found sex differences in epilepsy and autism, with epilepsy predominantly in female and ASD in male subjects. To understand the cellular and molecular mechanisms of the sex-difference, we performed whole cell patch clamp electrophysiology in mice and found hyperexcitability in female compared with male hippocampal CA1 neurons. We report the identification of sex-specific transcriptomic signatures resulting from ASH1L haploinsufficiency. Differentially expressed genes in female mice showed distinct association with epileptic encephalopathy, postnatal microcephaly and autistic behaviors. Thus, the role of ASH1L in specific circuits may be sex-dependent leading to sexual dimorphic effects from disruption of this gene.

neuroscience↗

bioRxiv2024

Dynamic Regulation Of The Chromatin Environment By ASH1L Modulates Human Neuronal Structure And Function

Precise regulation of the chromatin environment through post-translational histone modification modulates transcription and controls brain development. Not surprisingly, mutations in a large number of histone-modifying enzymes underlie complex brain disorders. In particular, the histone methyltransferase ASH1L modifies histone marks linked to transcriptional activation and has been implicated in multiple neuropsychiatric disorders. However, the mechanisms underlying the pathobiology of ASH1L-asociated disease remain underexplored. We generated human isogenic stem cells with a mutation in ASH1Ls catalytic domain. We find that ASH1L dysfunction results in reduced neurite outgrowth, which correlates with alterations in the chromatin profile of activating and repressive histone marks, as well as the dysregulation of gene programs important for neuronal structure and function implicated in neuropsychiatric disease. We also identified a novel regulatory node implicating both the SP and Kruppel-like families of transcription factors and ASH1L relevant to human neuronal development. Finally, we rescue cellular defects linked to ASH1L dysfunction by leveraging two independent epigenetic mechanisms that promote transcriptional activation. In summary, we identified an ASH1L-driven epigenetic and transcriptional axis essential for human brain development and complex brain disorders that provide insights into future therapeutic strategies for ASH1L-related disorders.

neuroscience↗

bioRxiv2022

Dysregulation of The Chromatin Environment Leads to Differential Alternative Splicing as A Mechanism Of Disease In a Human Model of Autism Spectrum Disorders

Autism spectrum disorder (ASD) affects 1 in 44 children. Chromatin regulatory proteins are overrepresented among genes that contain high risk variants in ASD. Disruption of the chromatin environment leads to widespread dysregulation of gene expression, which is traditionally thought as a mechanism of disease pathogenesis associated with ASD. Alternatively, alterations in chromatin dynamics could also lead to dysregulation of alternative splicing, which is understudied as a mechanism of ASD pathogenesis. The anticonvulsant valproic acid (VPA) is a well-known environmental risk factor for ASD that acts as a class I histone deacetylase (HDAC) inhibitor. However, the precise molecular mechanisms underlying defects in human neuronal development associated with exposure to VPA are understudied. To dissect how VPA exposure and subsequent chromatin hyperacetylation influence molecular signatures involved in ASD pathogenesis, we conducted RNA sequencing (RNA-seq) in human cortical neurons that were treated with VPA. We observed that differentially expressed genes (DEGs) were enriched for mRNA splicing, mRNA processing, histone modification, and metabolism related gene sets. Furthermore, we observed widespread increase in the number and the type of alternative splicing events. Analysis of differential transcript usage (DTU) showed that exposure to VPA induces extensive alterations in transcript isoform usage across neurodevelopmentally important genes. Finally, we find that DEGs and genes that display DTU overlap with known ASD-risk genes. Together, these findings suggest that, in addition to differential gene expression, changes in alternative splicing correlated with alterations in the chromatin environment could act as an additional mechanism of disease in ASD.

neuroscience↗

bioRxiv2021

Overcoming the effect of ASH1L haploinsufficiency on stem cells amenability to genome editing and differentiation into the neuronal lineage - a technical report

Genome editing and neuronal differentiation protocols have proliferated in the last decade. Mutations in genes that control pluripotency could lead to a potential obstacle with regards to the survival and differentiation potential of the genome-edited cell lines. Here we describe a protocol for the generation, and differentiation, of cell lines containing CRISPR/Cas9 induced mutations in the histone methyl transferase ASH1L. This chromatin modifier was previously implicated in hematopoietic stem cell pluripotency and is a major genetic risk factor for autism spectrum disorders (ASD). We find that haploinsufficiency of ASH1L leads to decreased NANOG gene expression leading to reduce cell survival and increased spontaneous differentiation. We report a method that provides improved single-cell survival with higher colony formation efficiency in ASH1L mutant stem cells. Additionally, we describe a modified dual-SMAD inhibition neuronal induction methodology that permits the successful generation of human neurons with mutations in ASH1L, in a smaller scale than previously reported methods. With our modified CRISPR-genome editing and neuronal differentiation protocols, it is possible to generate genome-edited stem cells containing mutations in genes that impact pluripotency and could affect subsequent cell lineage specific differentiation. Our detailed technical report presents cost-effective strategies that will benefit researchers focusing on both translational and basic science using stem cell experimental systems.

neuroscience↗

bioRxiv2018

Human neurons from Christianson syndrome iPSCs reveal allele-specific responses to rescue strategies

Human genetic disorders provide a powerful lens to understanding the human brain. Induced pluripotent stem cells (iPSC) represent an important, new resource for mechanistic studies and therapeutic development. Christianson syndrome (CS), an X-linked neurological disorder with attenuation of brain growth postnatally (postnatal microcephaly), is caused by mutations in SLC9A6, the gene encoding endosomal Na+/H+ exchanger 6 (NHE6). We developed CS iPSC lines from patients with a mutational spectrum, as well as robust biologically-related and isogenic controls. We demonstrate that mutations in CS lead to loss of protein function by a variety of mechanisms. Regardless of mutation, all patient-derived neurons demonstrate reduced neurite growth and arborization, likely underlying diminished postnatal brain growth in patients. Additionally, phenotype rescue strategies show allele-specific responses: a gene replacement strategy shows efficacy in nonsense mutations but not in a missense mutation, whereas application of exogenous trophic factors (BDNF or IGF-1) rescues arborization phenotypes across all mutations. Our data emphasize the important principle of personalized medicine whereby success of some therapeutic strategies may be more linked to patient genotype than others.

neuroscience↗