The Histone Methyltransferase Gene Absent, Small, or Homeotic Discs-1 Like Is Required for Normal Hox Gene Expression and Fertility in Mice

In silico identification of novel pre-microRNA genes in Rift valley fever virus suggest new pathomechanisms for embryo-fetal dysgenesis

MicroRNAs (miRNAs) are small non-coding RNAs that regulate the post-transcriptional expression of target genes. Virus-encoded miRNAs play an important role in the replication of viruses, modulate gene expression in both the virus and host, and affect their persistence and immune evasion in hosts. This renders viral miRNAs as potential targets for therapeutic applications, especially against pathogenic viruses that infect humans and animals. Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic RNA virus that causes severe disease in both humans and livestock. High mortality among newborn lambs and abortion storms are key characteristics of an RVF outbreak. To date, limited information is available on RVFV-derived miRNAs. In this study, computational methods were used to analyse the RVFV genome for putative pre-miRNA genes, which were then analysed for the presence of mature miRNAs. We detected 19 RVFV-encoded miRNAs and identified their potential mRNAs targets in sheep (Ovis aries), the most susceptible host. The identification of significantly enriched O. aries genes in association with RVFV miRNAs will help elucidate the molecular mechanisms underlying RVFV pathogenesis and potentially uncover novel drug targets for RVFV.

ASH1L guards cis-regulatory elements against cyclobutane pyrimidine dimer induction

The histone methyltransferase ASH1L, first discovered for its role in transcription, has been shown to accelerate the removal of ultraviolet (UV) light-induced cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair. Previous reports demonstrated that CPD excision is most efficient at transcriptional regulatory elements, including enhancers, relative to other genomic sites. Therefore, we analyzed DNA damage maps in ASH1L-proficient and ASH1L-deficient cells to understand how ASH1L controls enhancer stability. This comparison showed that ASH1L protects enhancer sequences against the induction of CPDs besides stimulating repair activity. ASH1L reduces CPD formation at C-containing but not at TT dinucleotides, and no protection occurs against pyrimidine-(6,4)-pyrimidone photoproducts or cisplatin crosslinks. The diminished CPD induction extends to gene promoters but excludes retrotransposons. This guardian role against CPDs in regulatory elements is associated with the presence of H3K4me3 and H3K27ac histone marks, which are known to interact with the PHD and BRD motifs of ASH1L, respectively. Molecular dynamics simulations identified a DNA-binding AT hook of ASH1L that alters the distance and dihedral angle between neighboring C nucleotides to disfavor dimerization. The loss of this protection results in a higher frequency of C->T transitions at enhancers of skin cancers carrying ASH1L mutations compared to ASH1L-intact counterparts.

The ASH1L-AS1-ASH1L axis controls NME1-mediated activation of the RAS signaling in gastric cancer

Gastric cancer (GC) is one of the most leading cause of malignancies. However, the molecular mechanisms underlying stomach carcinogenesis remain incompletely understood. Dysregulated genetic and epigenetic alternations significantly contribute to GC development. Here, we report that ASH1L and its antisense lncRNA ASH1L-AS1, which are transcribed from the most significant GC-risk signal at 1q22, act as novel oncogenes. The high levels of ASH1L or lncRNA ASH1L-AS1 expression in GC specimens are associated with worse prognosis of patients. In line with this, ASH1L and ASH1L-AS1 are functionally important in promoting GC disease progression. LncRNA ASH1L-AS1 up-regulates ASH1L transcription, increases histone methyltransferase ASH1L expression and elevates genome-wide H3K4me3 modification levels in GC cells. Furthermore, ASH1L-AS1 directly interacts with transcription factor NME1 protein to form the ASH1L-AS1-NME1 ribonucleoprotein, which transcriptionally promotes expression of ASH1L, ASH1L-AS1, KRAS and RAF1, and activates the RAS signaling pathway in GC cells. Taken together, our data demonstrated that the ASH1L-AS1-ASH1L regulatory axis controls histone modification reprogram and activation of the RAS signaling in cancers. Thus, ASH1L-AS1 might be a novel targets of GC therapeutics and diagnosis in the clinic.

ASH1L-MRG15 methyltransferase deposits H3K4me3 and FACT for damage verification in nucleotide excision repair

To recognize DNA adducts, nucleotide excision repair (NER) deploys the XPC sensor, which detects damage-induced helical distortions, followed by engagement of TFIIH for lesion verification. Accessory players ensure that this factor handover takes place in chromatin where DNA is tightly wrapped around histones. Here, we describe how the histone methyltransferase ASH1L, once activated by MRG15, helps XPC and TFIIH to navigate through chromatin and induce global-genome NER hotspots. Upon UV irradiation, ASH1L adds H3K4me3 all over the genome (except in active gene promoters), thus priming chromatin for XPC relocations from native to damaged DNA. The ASH1L-MRG15 complex further recruits the histone chaperone FACT to DNA lesions. In the absence of ASH1L, MRG15 or FACT, XPC is misplaced and persists on damaged DNA without being able to deliver the lesions to TFIIH. We conclude that ASH1L-MRG15 makes damage verifiable by the NER machinery through the sequential deposition of H3K4me3 and FACT.

To incise or not and where: SET-domain methyltransferases know

The concept of the histone code posits that histone modifications regulate gene functions once interpreted by epigenetic readers. A well-studied case is trimethylation of lysine 4 of histone H3 (H3K4me3), which is enriched at gene promoters. However, H3K4me3 marks are not needed for the expression of most genes, suggesting extra roles, such as influencing the 3D genome architecture. Here, we highlight an intriguing analogy between the H3K4me3-dependent induction of double-strand breaks in several recombination events and the impact of this same mark on DNA incisions for the repair of bulky lesions. We propose that Su(var)3-9, Enhancer-of-zeste and Trithorax (SET)-domain methyltransferases generate H3K4me3 to guide nucleases into chromatin spaces, the favorable accessibility of which ensures that DNA break intermediates are readily processed, thereby safeguarding genome stability.

Histone lysine methyltransferase-related neurodevelopmental disorders: current knowledge and saRNA future therapies

Neurodevelopmental disorders encompass a group of debilitating diseases presenting with motor and cognitive dysfunction, with variable age of onset and disease severity. Advances in genetic diagnostic tools have facilitated the identification of several monogenic chromatin remodeling diseases that cause Neurodevelopmental disorders. Chromatin remodelers play a key role in the neuro-epigenetic landscape and regulation of brain development; it is therefore not surprising that mutations, leading to loss of protein function, result in aberrant neurodevelopment. Heterozygous, usually de novo mutations in histone lysine methyltransferases have been described in patients leading to haploinsufficiency, dysregulated protein levels and impaired protein function. Studies in animal models and patient-derived cell lines, have highlighted the role of histone lysine methyltransferases in the regulation of cell self-renewal, cell fate specification and apoptosis. To date, in depth studies of histone lysine methyltransferases in oncology have provided strong evidence of histone lysine methyltransferase dysregulation as a determinant of cancer progression and drug resistance. As a result, histone lysine methyltransferases have become an important therapeutic target for the treatment of different cancer forms. Despite recent advances, we still lack knowledge about the role of histone lysine methyltransferases in neuronal development. This has hampered both the study and development of precision therapies for histone lysine methyltransferases-related Neurodevelopmental disorders. In this review, we will discuss the current knowledge of the role of histone lysine methyltransferases in neuronal development and disease progression. We will also discuss how RNA-based technologies using small-activating RNAs could potentially provide a novel therapeutic approach for the future treatment of histone lysine methyltransferase haploinsufficiency in these Neurodevelopmental disorders, and how they could be first tested in state-of-the-art patient-derived neuronal models.

Set2 family regulates mycotoxin metabolism and virulence via H3K36 methylation in pathogenic fungus Aspergillus flavus

Aspergillus flavus infects various crops with aflatoxins, and leads to aspergillosis opportunistically. Though H3K36 methylation plays an important role in fungal toxin metabolism and virulence, no data about the biological function of H3K36 methylation in A. flavus virulence has been reported. Our study showed that the Set2 histone methyltransferase family, AshA and SetB, involves in morphogenesis and mycotoxin anabolism by regulating related transcriptional factors, and they are important for fungal virulence to crops and animals. Western-blotting and double deletion analysis revealed that AshA mainly regulates H3K36me2, whereas SetB is mainly responsible for H3K36me3 in the nucleus. By construction of domain deletion A. flavus strain and point mutation strains by homologous recombination, the study revealed that SET domain is indispensable in mycotoxin anabolism and virulence of A. flavus, and N455 and V457 in it are the key amino acid residues. ChIP analysis inferred that the methyltransferase family controls fungal reproduction and regulates the production of AFB1 by directly regulating the production of the transcriptional factor genes, including wetA, steA, aflR and amylase, through H3K36 trimethylation in their chromatin fragments, based on which this study proposed that, by H3K36 trimethylation, this methyltransferase family controls AFB1 anabolism through transcriptional level and substrate utilization level. This study illuminates the epigenetic mechanism of the Set2 family in regulating fungal virulence and mycotoxin production, and provides new targets for controlling the virulence of the fungus A. flavus.

AUTHOR SUMMARY

The methylation of H3K36 plays an important role in the fungal secondary metabolism and virulence, but no data about the regulatory mechanism of H3K36 methylation in the virulence of A. flavus have been reported. Our study revealed that, in the histone methyltransferase Set2 family, AshA mainly catalyzes H3K36me2, and involves in the methylation of H3K36me1, and SetB mainly catalyzes H3K36me3 and H3K36me1. Through domain deletion and point mutation analysis, this study also revealed that the SET domain was critical for the normal biological function of the Set2 family and that N455 and V457 in the domain were critical for AshA. By ChIP-seq and ChIP-qPCR analysis, H3K36 was found to be trimethylation modified in the promotors and ORF positions of wetA, steA, aflR and the amylase gene (AFLA_084340), and further qRT-PCR results showed that these methylation modifications regulate the expression levels of these genes. According to the results of ChIP-seq analysis, we proposed that, by H3K36 trimethylation, this methyltransferase family controls the metabolism of mycotoxin through transcriptional level and substrate utilization level. All the results from this study showed that Set2 family is essential for fungal secondary metabolism and virulence, which lays a theoretical groundwork in the early prevention and treatment of A. flavus pollution, and also provides an effective strategy to fight against other pathogenic fungi.

Role of HOXA9 in solid tumors: mechanistic insights and therapeutic potential

HOXA9 functioning as a transcription factor is one of the members of HOX gene family, which governs multiple cellular activities by facilitating cellular signal transduction. In addition to be a driver in AML which has been widely studied, the role of HOXA9 in solid tumor progression has also received increasing attention in recent years, where the aberrant expression of HOXA9 is closely associated with the prognosis of patient. This review details the signaling pathways, binding partners, post-transcriptional regulation of HOXA9, and possible inhibitors of HOXA9 in solid tumors, which provides a reference basis for further study on the role of HOXA9 in solid tumors.

Modelling Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) Using Mice and Zebrafish

Autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD) are two debilitating neurodevelopmental disorders. The former is associated with social impairments whereas the latter is associated with inattentiveness, hyperactivity, and impulsivity. There is recent evidence that both disorders are somehow related and that genes may play a large role in these disorders. Despite mounting human and animal research, the neurological pathways underlying ASD and ADHD are still not well understood. Scientists investigate neurodevelopmental disorders by using animal models that have high similarities in genetics and behaviours with humans. Mice have been utilized in neuroscience research as an excellent animal model for a long time; however, the zebrafish has attracted much attention recently, with an increasingly large number of studies using this model. In this review, we first discuss ASD and ADHD aetiology from a general point of view to their characteristics and treatments. We also compare mice and zebrafish for their similarities and discuss their advantages and limitations in neuroscience. Finally, we summarize the most recent and existing research on zebrafish and mouse models of ASD and ADHD. We believe that this review will serve as a unique document providing interesting information to date about these models, thus facilitating research on ASD and ADHD.

Counteracting epigenetic mechanisms regulate the structural development of neuronal circuitry in human neurons

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. Genetic findings suggest that there is an overrepresentation of chromatin regulatory genes among the genes associated with ASD. ASH1 like histone lysine methyltransferase (ASH1L) was identified as a major risk factor for ASD. ASH1L methylates Histone H3 on Lysine 36, which is proposed to result primarily in transcriptional activation. However, how mutations in ASH1L lead to deficits in neuronal connectivity associated with ASD pathogenesis is not known. We report that ASH1L regulates neuronal morphogenesis by counteracting the catalytic activity of Polycomb Repressive complex 2 group (PRC2) in stem cell-derived human neurons. Depletion of ASH1L decreases neurite outgrowth and decreases expression of the gene encoding the neurotrophin receptor TrkB whose signaling pathway is linked to neuronal morphogenesis. The neuronal morphogenesis defect is overcome by inhibition of PRC2 activity, indicating that a balance between the Trithorax group protein ASH1L and PRC2 activity determines neuronal morphology. Thus, our work suggests that ASH1L may epigenetically regulate neuronal morphogenesis by modulating pathways like the BDNF-TrkB signaling pathway. Defects in neuronal morphogenesis could potentially impair the establishment of neuronal connections which could contribute to the neurodevelopmental pathogenesis associated with ASD in patients with ASH1L mutations.

Reprogramming of the epigenome in neurodevelopmental disorders

The etiology of neurodevelopmental disorders (NDDs) remains a challenge for researchers. Human brain development is tightly regulated and sensitive to cellular alterations caused by endogenous or exogenous factors. Intriguingly, the surge of clinical sequencing studies has revealed that many of these disorders are monogenic and monoallelic. Notably, chromatin regulation has emerged as highly dysregulated in NDDs, with many syndromes demonstrating phenotypic overlap, such as intellectual disabilities, with one another. Here we discuss epigenetic writers, erasers, readers, remodelers, and even histones mutated in NDD patients, predicted to affect gene regulation. Moreover, this review focuses on disorders associated with mutations in enzymes involved in histone acetylation and methylation, and it highlights syndromes involving chromatin remodeling complexes. Finally, we explore recently discovered histone germline mutations and their pathogenic outcome on neurological function. Epigenetic regulators are mutated at every level of chromatin organization. Throughout this review, we discuss mechanistic investigations, as well as various animal and iPSC models of these disorders and their usefulness in determining pathomechanism and potential therapeutics. Understanding the mechanism of these mutations will illuminate common pathways between disorders. Ultimately, classifying these disorders based on their effects on the epigenome will not only aid in prognosis in patients but will aid in understanding the role of epigenetic machinery throughout neurodevelopment.

Deficiency of autism risk factor ASH1L in prefrontal cortex induces epigenetic aberrations and seizures

ASH1L, a histone methyltransferase, is identified as a top-ranking risk factor for autism spectrum disorder (ASD), however, little is known about the biological mechanisms underlying the link of ASH1L haploinsufficiency to ASD. Here we show that ASH1L expression and H3K4me3 level are significantly decreased in the prefrontal cortex (PFC) of postmortem tissues from ASD patients. Knockdown of Ash1L in PFC of juvenile mice induces the downregulation of risk genes associated with ASD, intellectual disability (ID) and epilepsy. These downregulated genes are enriched in excitatory and inhibitory synaptic function and have decreased H3K4me3 occupancy at their promoters. Furthermore, Ash1L deficiency in PFC causes the diminished GABAergic inhibition, enhanced glutamatergic transmission, and elevated PFC pyramidal neuronal excitability, which is associated with severe seizures and early mortality. Chemogenetic inhibition of PFC pyramidal neuronal activity, combined with the administration of GABA enhancer diazepam, rescues PFC synaptic imbalance and seizures, but not autistic social deficits or anxiety-like behaviors. These results have revealed the critical role of ASH1L in regulating synaptic gene expression and seizures, which provides insights into treatment strategies for ASH1L-associated brain diseases.

Discovery of first-in-class inhibitors of ASH1L histone methyltransferase with anti-leukemic activity

ASH1L histone methyltransferase plays a crucial role in the pathogenesis of different diseases, including acute leukemia. While ASH1L represents an attractive drug target, developing ASH1L inhibitors is challenging, as the catalytic SET domain adapts an inactive conformation with autoinhibitory loop blocking the access to the active site. Here, by applying fragment-based screening followed by medicinal chemistry and a structure-based design, we developed first-in-class small molecule inhibitors of the ASH1L SET domain. The crystal structures of ASH1L-inhibitor complexes reveal compound binding to the autoinhibitory loop region in the SET domain. When tested in MLL leukemia models, our lead compound, AS-99, blocks cell proliferation, induces apoptosis and differentiation, downregulates MLL fusion target genes, and reduces the leukemia burden in vivo. This work validates the ASH1L SET domain as a druggable target and provides a chemical probe to further study the biological functions of ASH1L as well as to develop therapeutic agents.

Role of Ash1l in Tourette syndrome and other neurodevelopmental disorders

Ash1l potentially contributes to neurodevelopmental diseases. Although specific Ash1l mutations are rare, they have led to informative studies in animal models that may bring therapeutic advances. Ash1l is highly expressed in the brain and correlates with the neuropathology of Tourette syndrome (TS), autism spectrum disorder, and intellectual disability during development, implicating shared epigenetic factors and overlapping neuropathological mechanisms. Functional convergence of Ash1l generated several significant signaling pathways: chromatin remodeling and transcriptional regulation, protein synthesis and cellular metabolism, and synapse development and function. Here, we systematically review the literature on Ash1l, including its discovery, expression, function, regulation, implication in the nervous system, signaling pathway, mutations, and putative involvement in TS and other neurodevelopmental traits. Such findings highlight Ash1l pleiotropy and the necessity of transcending a single gene to complicated mechanisms of network convergence underlying these diseases. With the progress in functional genomic analysis (highlighted in this review), and although the importance and necessity of Ash1l becomes increasingly apparent in the medical field, further research is required to discover the precise function and molecular regulatory mechanisms related to Ash1l. Thus, a new perspective is proposed for basic scientific research and clinical interventions for cross‐disorder diseases.

Experimental Models to Study Autism Spectrum Disorders: hiPSCs, Rodents and Zebrafish

Autism Spectrum Disorders (ASD) affect around 1.5% of the global population, which manifest alterations in communication and socialization, as well as repetitive behaviors or restricted interests. ASD is a complex disorder with known environmental and genetic contributors; however, ASD etiology is far from being clear. In the past decades, many efforts have been put into developing new models to study ASD, both in vitro and in vivo. These models have a lot of potential to help to validate some of the previously associated risk factors to the development of the disorder, and to test new potential therapies that help to alleviate ASD symptoms. The present review is focused on the recent advances towards the generation of models for the study of ASD, which would be a useful tool to decipher the bases of the disorder, as well as to conduct drug screenings that hopefully lead to the identification of useful compounds to help patients deal with the symptoms of ASD.

Knockdown of ASH1L methyltransferase induced apoptosis inhibiting proliferation and H3K36 methylation in bovine cumulus cells

This study aims to investigate the expression and function of absent, small, or homeotic 1-like (ASH1L) methyltransferase in bovine cumulus cells in order to reveal by which mechanisms ASH1L regulates epigenetic modification and apoptosis in cumulus cells. The location of ASH1L and the methylation pattern of H3K36 were detected using immunofluorescence staining in cumulus cells. Quantitative PCR (qPCR) and western blotting were used to screen for effective siRNA targeting the ASH1L gene. Also, the mRNA expression levels of apoptosis-related genes and polycomb inhibitory complex genes were estimated by qPCR after knocking down the ASH1L gene in bovine cumulus cells. Cell proliferation and apoptosis were measured with the CCK-8 method and Annexin V-FITC by flow cytometry, respectively. The results of immunofluorescence analysis showed that ASH1L is located in the nucleus of bovine cumulus cells and is distributed in a dotted pattern. ASH1L knockdown in cumulus cells induced a decrease in the levels of H3K36me1/2/3 methylation (P < 0.05). Additionally, ASH1L knockdown inhibited cell proliferation, increased the apoptosis rate, and upregulated the expression of apoptosis genes CASPASE-3, BAX and BAX/BCL-2 ratio (P < 0.05). Meanwhile, the mRNA expression levels of EZH2 and SUZ12, two subunits of PRC2 protein, were increased in cells with ASH1L knockdown (P < 0.05). Therefore, the expression of ASH1L methyltransferase and its function in on the apoptosis of bovine cumulus cells were first studied. The mechanism by which ASH1L regulates the histone methylation and apoptosis in cumulus cells was also revealed.

Mir142 loss unlocks IDH2R140-dependent leukemogenesis through antagonistic regulation of HOX genes

AML is a genetically heterogeneous disease and understanding how different co-occurring mutations cooperate to drive leukemogenesis will be crucial for improving diagnostic and therapeutic options for patients. MIR142 mutations have been recurrently detected in IDH-mutated AML samples. Here, we have used a mouse model to investigate the interaction between these two mutations and demonstrate a striking synergy between Mir142 loss-of-function and IDH2^R140Q, with only recipients of double mutant cells succumbing to leukemia. Transcriptomic analysis of the non-leukemic single and leukemic double mutant progenitors, isolated from these mice, suggested a novel mechanism of cooperation whereby Mir142 loss-of-function counteracts aberrant silencing of Hoxa cluster genes by IDH2^R140Q. Our analysis suggests that IDH2^R140Q is an incoherent oncogene, with both positive and negative impacts on leukemogenesis, which requires the action of cooperating mutations to alleviate repression of Hoxa genes in order to advance to leukemia. This model, therefore, provides a compelling rationale for understanding how different mutations cooperate to drive leukemogenesis and the context-dependent effects of oncogenic mutations.

A chromosome 1q22 microdeletion including ASH1L is associated with intellectual disability in a Chinese family

Background

Copy number variants (CNVs) associated with developmental delay and intellectual disability (DD/ID) continue to be identified in patients. This article reports identification of a chromosome 1q22 microdeletion as the genetic cause in a Chinese family affected by ID.

Case presentation

The proband was a 19-year-old pregnant woman referred for genetic counseling and prenatal diagnosis at 18 weeks of gestation. She had severe ID with basically normal stature (height 154 cm [0 SD], weight 61 kg [− 0.2 SD], and head circumference 54 cm [− 1.12 SD]). Her distinctive facial features included a prominent forehead; flat face; flat nasal bridge and a short upturned nose; thin lips; and small ears. The proband’s father was reported to have low intelligence, whereas her mother was of normal intelligence but with scoliosis. Chromosome microarray analysis (CMA) reveals that the proband, her father and the fetus all carry a 1q22 microdeletion of 936.3 Kb (arr[GRCh37] 1q22 (155016052_155952375)×1), which was not observed in her mother and paternal grandparents and uncles, suggesting a de novo mutation in the proband’s father. The microdeletion involves 24 OMIM genes including ASH1L (also known as KMT2H and encoding a histone lysine methyltransferase). Of note, haploinsufficiency of ASH1L has been shown to be associated with neurodevelopmental disorders. Based on the inheritance of the detected CNV in the pedigree and similar CNVs associated with ID in public databases (Decipher, DGV and ClinVar) and literature, the detected CNV is considered as pathogenic. The family chose to terminate the pregnancy.

Conclusions

The identified 1q22 microdeletion including ASH1L is pathogenic and associated with ID. This case broadens the spectrum of ID-related CNVs and may be useful as a reference for clinicians.

A chromatin scaffold for DNA damage recognition: how histone methyltransferases prime nucleosomes for repair of ultraviolet light-induced lesions

The excision of mutagenic DNA adducts by the nucleotide excision repair (NER) pathway is essential for genome stability, which is key to avoiding genetic diseases, premature aging, cancer and neurologic disorders. Due to the need to process an extraordinarily high damage density embedded in the nucleosome landscape of chromatin, NER activity provides a unique functional caliper to understand how histone modifiers modulate DNA damage responses. At least three distinct lysine methyltransferases (KMTs) targeting histones have been shown to facilitate the detection of ultraviolet (UV) light-induced DNA lesions in the difficult to access DNA wrapped around histones in nucleosomes. By methylating core histones, these KMTs generate docking sites for DNA damage recognition factors before the chromatin structure is ultimately relaxed and the offending lesions are effectively excised. In view of their function in priming nucleosomes for DNA repair, mutations of genes coding for these KMTs are expected to cause the accumulation of DNA damage promoting cancer and other chronic diseases. Research on the question of how KMTs modulate DNA repair might pave the way to the development of pharmacologic agents for novel therapeutic strategies.

Mutations in ASH1L confer susceptibility to Tourette syndrome

Tourette syndrome (TS) is a childhood-onset neuropsychiatric disorder characterized by repetitive motor movements and vocal tics. The clinical manifestations of TS are complex and often overlap with other neuropsychiatric disorders. TS is highly heritable; however, the underlying genetic basis and molecular and neuronal mechanisms of TS remain largely unknown. We performed whole-exome sequencing of a hundred trios (probands and their parents) with detailed records of their clinical presentations and identified a risk gene, ASH1L, that was both de novo mutated and associated with TS based on a transmission disequilibrium test. As a replication, we performed follow-up targeted sequencing of ASH1L in additional 524 unrelated TS samples and replicated the association (P value = 0.001). The point mutations in ASH1L cause defects in its enzymatic activity. Therefore, we established a transgenic mouse line and performed an array of anatomical, behavioral, and functional assays to investigate ASH1L function. The Ash1l^+/- mice manifested tic-like behaviors and compulsive behaviors that could be rescued by the tic-relieving drug haloperidol. We also found that Ash1l disruption leads to hyper-activation and elevated dopamine-releasing events in the dorsal striatum, all of which could explain the neural mechanisms for the behavioral abnormalities in mice. Taken together, our results provide compelling evidence that ASH1L is a TS risk gene.

The Trithorax protein Ash1L promotes myoblast fusion by activating Cdon expression

Myoblast fusion (MF) is required for muscle growth and repair, and its alteration contributes to muscle diseases. The mechanisms governing this process are incompletely understood, and no epigenetic regulator has been previously described. Ash1L is an epigenetic activator belonging to the Trithorax group of proteins and is involved in FSHD muscular dystrophy, autism and cancer. Its physiological role in skeletal muscle is unknown. Here we report that Ash1L expression is positively correlated with MF and reduced in Duchenne muscular dystrophy. In vivo, ex vivo and in vitro experiments support a selective and evolutionary conserved requirement for Ash1L in MF. RNA- and ChIP-sequencing indicate that Ash1L is required to counteract Polycomb repressive activity to allow activation of selected myogenesis genes, in particular the key MF gene Cdon. Our results promote Ash1L as an important epigenetic regulator of MF and suggest that its activity could be targeted to improve cell therapy for muscle diseases.

Myoblast fusion in skeletal muscle is a complex process but how this is regulated is unclear. Here, the authors identify Ash1L, a histone methyltransferase, as modulating myoblast fusion via activation of the myogenesis gene Cdon, and observe decreased Ash1L expression in Duchenne muscular dystrophy.

Epigenetic Control of Mesenchymal Stem Cell Fate Decision via Histone Methyltransferase Ash1l

Previous research indicates that knocking out absent, small, or homeotic-like (Ash1l) in mice, a histone 3 lysine 4 (H3K4) trimethyltransferase, can result in arthritis with more severe cartilage and bone destruction. Research has documented the essential role of Ash1l in stem cell fate decision such as hematopoietic stem cells and the progenitors of keratinocytes. Following up on those insights, our research seeks to document the function of Ash1l in skeletal formation, specifically whether it controls the fate decision of mesenchymal progenitor cells. Our findings indicate that in osteoporotic bones, Ash1l was significantly decreased, indicating a positive correlation between bone mass and the expression of Ash1l. Silencing of Ash1l that had been markedly upregulated in differentiated C3H10T1/2 (C3) cells hampered osteogenesis and chondrogenesis but promoted adipogenesis. Consistently, overexpression of an Ash1l SET domain-containing fragment 3 rather than Ash1lΔN promoted osteogenic and chondrogenic differentiation of C3 cells and simultaneously inhibited adipogenic differentiation. This indicates that the role of Ash1l in regulating the differentiation of C3 cells is linked to its histone methyltransferase activity. Subcutaneous ex vivo transplantation experiments confirmed the role of Ash1l in the promotion of osteogenesis. Further experiments proved that Ash1l can epigenetically affect the expression of essential osteogenic and chondrogenic transcription factors. It exerts this impact via modifications in the enrichment of H3K4me3 on their promoter regions. Considering the promotional action of Ash1l on bone, it could potentially prompt new therapeutic strategy to promote osteogenesis. Stem Cells 2019;37:115-127.

Histone Lysine Methylases and Demethylases in the Landscape of Human Developmental Disorders

Histone lysine methyltransferases (KMTs) and demethylases (KDMs) underpin gene regulation. Here we demonstrate that variants causing haploinsufficiency of KMTs and KDMs are frequently encountered in individuals with developmental disorders. Using a combination of human variation databases and existing animal models, we determine 22 KMTs and KDMs as additional candidates for dominantly inherited developmental disorders. We show that KMTs and KDMs that are associated with, or are candidates for, dominant developmental disorders tend to have a higher level of transcription, longer canonical transcripts, more interactors, and a higher number and more types of post-translational modifications than other KMT and KDMs. We provide evidence to firmly associate KMT2C, ASH1L, and KMT5B haploinsufficiency with dominant developmental disorders. Whereas KMT2C or ASH1L haploinsufficiency results in a predominantly neurodevelopmental phenotype with occasional physical anomalies, KMT5B mutations cause an overgrowth syndrome with intellectual disability. We further expand the phenotypic spectrum of KMT2B-related disorders and show that some individuals can have severe developmental delay without dystonia at least until mid-childhood. Additionally, we describe a recessive histone lysine-methylation defect caused by homozygous or compound heterozygous KDM5B variants and resulting in a recognizable syndrome with developmental delay, facial dysmorphism, and camptodactyly. Collectively, these results emphasize the significance of histone lysine methylation in normal human development and the importance of this process in human developmental disorders. Our results demonstrate that systematic clinically oriented pathway-based analysis of genomic data can accelerate the discovery of rare genetic disorders.

Mrg15 stimulates Ash1 H3K36 methyltransferase activity and facilitates Ash1 Trithorax group protein function in Drosophila

Ash1 is a Trithorax group protein that possesses H3K36-specific histone methyltransferase activity, which antagonizes Polycomb silencing. Here we report the identification of two Ash1 complex subunits, Mrg15 and Nurf55. In vitro, Mrg15 stimulates the enzymatic activity of Ash1. In vivo, Mrg15 is recruited by Ash1 to their common targets, and Mrg15 reinforces Ash1 chromatin association and facilitates the proper deposition of H3K36me2. To dissect the functional role of Mrg15 in the context of the Ash1 complex, we identify an Ash1 point mutation (Ash1-R1288A) that displays a greatly attenuated interaction with Mrg15. Knock-in flies bearing this mutation display multiple homeotic transformation phenotypes, and these phenotypes are partially rescued by overexpressing the Mrg15-Nurf55 fusion protein, which stabilizes the association of Mrg15 with Ash1. In summary, Mrg15 is a subunit of the Ash1 complex, a stimulator of Ash1 enzymatic activity and a critical regulator of the TrxG protein function of Ash1 in Drosophila.

ASH1L histone methyltransferase regulates the handoff between damage recognition factors in global-genome nucleotide excision repair

Global-genome nucleotide excision repair (GG-NER) prevents ultraviolet (UV) light-induced skin cancer by removing mutagenic cyclobutane pyrimidine dimers (CPDs). These lesions are formed abundantly on DNA wrapped around histone octamers in nucleosomes, but a specialized damage sensor known as DDB2 ensures that they are accessed by the XPC initiator of GG-NER activity. We report that DDB2 promotes CPD excision by recruiting the histone methyltransferase ASH1L, which methylates lysine 4 of histone H3. In turn, methylated H3 facilitates the docking of the XPC complex to nucleosomal histone octamers. Consequently, DDB2, ASH1L and XPC proteins co-localize transiently on histone H3-methylated nucleosomes of UV-exposed cells. In the absence of ASH1L, the chromatin binding of XPC is impaired and its ability to recruit downstream GG-NER effectors diminished. Also, ASH1L depletion suppresses CPD excision and confers UV hypersensitivity. These findings show that ASH1L configures chromatin for the effective handoff between damage recognition factors during GG-NER activity.

Dysregulation of an X-linked primate-specific epididymal microRNA cluster in unexplained asthenozoospermia

Asthenoszoopermia, characterized by reduced sperm motility, is one of the primary forms of male infertility. Whereas most cases were diagnosed into unexplained asthenozoospermia (UA) because the etiology cannot be identified. In animal models, epigenetic dysregulation in epididymis can impair sperm maturation and result in asthenozoospermia. However, researches of epididymal epigenetic regulation on humans are impeded by the difficulty in obtaining epididymal tissues. We previously identified cell-free seminal microRNAs predominately derived from epididymis in human ejaculate. In the present study, these microRNAs were used to screen and validate the microRNA dysregulation in men with UA, which were divided into screening set and validation set. The expression of five miRNAs (miR-891b, miR-892b, miR-892a, miR-888 and miR-890) was found and confirmed to be dysregulated in men with UA. Interestingly, these five miRNAs belong to a primate-specific miRNA cluster located on the X chromosome with epididymis specific expression. Moreover, obvious coherent dysregulation of these miRNAs were observed in 13% men with UA. Regression analysis demonstrated that levels of these miRNAs were significantly correlated with progressive sperm motility. Functions and pathways of predicted target genes of this cluster suggested its role in sperm maturation. Dysregulation of this miRNA cluster might be an epigenetic basis for some patients with UA. We also showed a noninvasive and feasible approach to get epigenetic information of human epididymis.

Novel MCA/ID syndrome with ASH1L mutation

We identified a novel mutation in ASH1L in a patient with severe intellectual disability, growth failure, microcephaly, facial dysmorphism, myelination delay, and skeletal abnormalities. ASH1L is a histone methyltransferase that associates with the transcribed region of all active genes examined, including Hox genes. It catalyzes H3K36 methylation and plays important roles in development. There has been increasing evidence that heterozygous mutation of ASH1L is associated with ID and autism spectrum disorders. We suggest that ASH1L abnormalities may cause a novel MCA/ID syndrome.