MYT1L haploinsufficiency in human neurons and mice causes autism-associated phenotypes that can be reversed by genetic and pharmacologic intervention

Abstract

MYT1L is an autism spectrum disorder (ASD)-associated transcription factor that is expressed in virtually all neurons throughout life. How MYT1L mutations cause neurological phenotypes and whether they can be targeted remains enigmatic. Here, we examine the effects of MYT1L deficiency in human neurons and mice. Mutant mice exhibit neurodevelopmental delays with thinner cortices, behavioural phenotypes, and gene expression changes that resemble those of ASD patients. MYT1L target genes, including WNT and NOTCH, are activated upon MYT1L depletion and their chemical inhibition can rescue delayed neurogenesis in vitro. MYT1L deficiency also causes upregulation of the main cardiac sodium channel, SCN5A, and neuronal hyperactivity, which could be restored by shRNA-mediated knockdown of SCN5A or MYT1L overexpression in postmitotic neurons. Acute application of the sodium channel blocker, lamotrigine, also rescued electrophysiological defects in vitro and behaviour phenotypes in vivo. Hence, MYT1L mutation causes both developmental and postmitotic neurological defects. However, acute intervention can normalise resulting electrophysiological and behavioural phenotypes in adulthood.

MYT1L deficiency impairs excitatory neuron trajectory during cortical development

“…To date, there are three transgenic mouse models that disrupt different exons of MYT1L that converge on a hyperactivity phenotype, while other behaviors are varied likely because different assays were used 12,13,15 . A study by Weigel et al 14 performed scRNAseq on the neonatal (P0) forebrain from the mice described in Wohr et al 15 and found a decreased number of newly formed neurons in the subventricular zone. Additionally, the authors observed an increased expression of non-neuronal gene expression programs which can perturb neuronal cell identity.…”

“…Given the widespread expression pattern of MYT1L in neurons, it is unclear if specific neuronal subtypes are more sensitive to MYT1L deficiency. Likewise, previous studies using bulk RNA sequencing have shown that MYT1L deficiency affects genes associated with the cell cycle 11,12,14 , differentiation 9,10 , and proliferation 22 . However, a limitation of bulk sequencing is that it only provides average gene expression data from a mixed population of cells, making it challenging to discern the precise origin of observed differences.…”

“…To investigate the long-term effects of MYT1L deficiency on both cell proportion and transcriptional changes, we conducted a snRNAseq analysis of the cortex in juvenile male and female WT and MYT1L Het animals at P21, when neurogenesis is largely completed. Analysis of KOs are not possible as they are not viable postnatally [12][13][14] . We analyzed snRNAseq data from 96,505 nuclei to identify 19 types of excitatory neurons spanning cortical layers, 11 subtypes of inhibitory neurons, and 8 non-neuronal types using hierarchical correlation mapping, referencing the taxonomies and subclass annotations from the Allen Brain Cell (ABC) Atlas 19 (Figure 4A, Supplemental Figure 2).…”

“…Similarly, in vivo epigenetic studies of normal development show that MYT1L promotes neuronal differentiation by recruiting the SIN3B repressive complex to promoters and enhancers of postmitotic neurons to suppress early developmental programs 11 . Indeed, loss of MYT1L in multiple mouse models resulted in upregulation of a fetal gene expression signature [12][13][14] . To date, three pivotal studies have delved into the in vivo functions of MYT1L by creating transgenic mouse models.…”

“…Each study uniquely disrupted a different exon of MYT1L (6 in Wohr et al 15 , 7 in Chen et al 12 , and 9 in Kim et al 13 ). The animal models are valuable tools to study the molecular and cellular consequences of MYT1L haploinsufficiency and the mice recapitulate many of the clinical presentations such as hyperactivity, structural malformations, obesity, and behavioral deficits [12][13][14] . However, it remains largely unknown how MYT1L haploinsufficiency influences the trajectory of neuronal differentiation in vivo, and whether the development of specific neuronal subtypes is particularly susceptible to the loss of MYT1L.…”