The Role of ASH1L During Human Neurodevelopment

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. A significant proportion of ASD cases are of complex genetic etiology; complexity which might reflect the impact of gene-environment interactions. However, there is a gap in our understanding of the mechanisms that underlie the gene-environment interaction in autism complex etiology. Genome wide association studies in large ASD cohorts identified high risk variants associated with autism in genes that regulate histone modifications and remodel chromatin. These findings highlight the relevance of chromatin regulatory mechanisms in the pathology of ASD. Changes in Histone H3 methylation have been identified in a subset of neuronal genes in postmortem cerebral cortex of autism patients. ASH1L is a histone H3-methyltransferase that was previously identified in whole exome sequencing studies, as a gene strongly enriched for variants likely to increase ASD risk. However, the role of ASH1L during human neurodevelopment is not well understood on a cellular or molecular basis. To investigate ASH1L during human brain development, I analyzed developmental transcriptome data collected from donated post-mortem human brain tissue; tissues that was processed in the Allen Brain Atlas. My analysis suggests that ASH1L is active during early prenatal development, along with other genes important to chromatin modification. Furthermore, I find that co-expression network analysis implicates ASH1L in a cluster of genes important to the development of neuronal projections, protein ubiquitination, and neurotrophin signaling pathways. This analysis supports cellular and molecular phenotypes seen in ASH1L knockdown studies performed in human-induced neurons. Through these analyses, ASH1L is shown to be important both in early neurodevelopment, and to be strongly associated with ASD pathology

Multiubiquitination of TRPV4 reduces channel activity independent of surface localization

Ubiquitin (Ub)-mediated regulation of plasmalemmal ion channel activity canonically occurs via stimulation of endocytosis. Whether ubiquitination can modulate channel activity by alternative mechanisms remains unknown. Here, we show that the transient receptor potential vanilloid 4 (TRPV4) cation channel is multiubiquitinated within its cytosolic N-terminal and C-terminal intrinsically disordered regions (IDRs). Mutagenizing select lysine residues to block ubiquitination of the N-terminal but not C-terminal IDR resulted in a marked elevation of TRPV4-mediated intracellular calcium influx, without increasing cell surface expression levels. Conversely, enhancing TRPV4 ubiquitination via expression of an E3 Ub ligase reduced TRPV4 channel activity but did not decrease plasma membrane abundance. These results demonstrate Ub-dependent regulation of TRPV4 channel function independent of effects on plasma membrane localization. Consistent with ubiquitination playing a key negative modulatory role of the channel, gain-of-function neuropathy-causing mutations in the TRPV4 gene led to reduced channel ubiquitination in both cellular and Drosophila models of TRPV4 neuropathy, whereas increasing mutant TRPV4 ubiquitination partially suppressed channel overactivity. Together, these data reveal a novel mechanism via which ubiquitination of an intracellular flexible IDR domain modulates ion channel function independently of endocytic trafficking and identify a contributory role for this pathway in the dysregulation of TRPV4 channel activity by neuropathy-causing mutations