Untangle the Multi-Facet Functions of Auts2 as an Entry Point to Understand Neurodevelopmental Disorders

ImputeHiFI: An Imputation Method for Multiplexed DNA FISH Data by Utilizing Single-Cell Hi-C and RNA FISH Data

Although multiplexed DNA fluorescence in situ hybridization (FISH) enables tracking the spatial localization of thousands of genomic loci using probes within individual cells, the high rates of undetected probes impede the depiction of 3D chromosome structures. Current data imputation methods neither utilize single-cell Hi-C data, which elucidate 3D genome architectures using sequencing nor leverage multimodal RNA FISH data that reflect cell-type information, limiting the effectiveness of these methods in complex tissues such as the mouse brain. To this end, a novel multiplexed DNA FISH imputation method named ImputeHiFI is proposed, which fully utilizes the complementary structural information from single-cell Hi-C data and the cell type signature from RNA FISH data to obtain a high-fidelity and complete spatial location of chromatin loci. ImputeHiFI enhances cell clustering, compartment identification, and cell subtype detection at the single-cell level in the mouse brain. ImputeHiFI improves the recognition of cell-type-specific loops in three high-resolution datasets. In short, ImputeHiFI is a powerful tool capable of imputing multiplexed DNA FISH data from various resolutions and imaging protocols, facilitating studies of 3D genome structures and functions.

Fbrsl1 is required for heart development in Xenopus laevis and de novo variants in FBRSL1 can cause human heart defects

De novo truncating variants in fibrosin-like 1 (FBRSL1), a member of the AUTS2 gene family, cause a disability syndrome, including organ malformations such as heart defects. Here, we use Xenopus laevis to investigate whether Fbrsl1 plays a role in heart development. Xenopus laevis fbrsl1 is expressed in tissues relevant for heart development, and morpholino-mediated knockdown of Fbrsl1 results in severely hypoplastic hearts. Our data suggest that Fbrsl1 is required for the development of the first heart field, which contributes to the ventricle and the atria, but not for the second heart field, which gives rise to the outflow tract. The morphant heart phenotype could be rescued using a human N-terminal FBRSL1 isoform that contains an alternative exon, but lacks the AUTS2 domain. N-terminal isoforms carrying patient variants failed to rescue. Interestingly, a long human FBRSL1 isoform, harboring the AUTS2 domain, also did not rescue the morphant heart defects. Thus, our data suggest that different FBRSL1 isoforms may have distinct functions and that only the short N-terminal isoform, appears to be critical for heart development.

Fetal brain response to maternal inflammation requires microglia

In utero infection and maternal inflammation can adversely impact fetal brain development. Maternal systemic illness, even in the absence of direct fetal brain infection, is associated with an increased risk of neuropsychiatric disorders in affected offspring. The cell types mediating the fetal brain response to maternal inflammation are largely unknown, hindering the development of novel treatment strategies. Here, we show that microglia, the resident phagocytes of the brain, highly express receptors for relevant pathogens and cytokines throughout embryonic development. Using a rodent maternal immune activation (MIA) model in which polyinosinic:polycytidylic acid is injected into pregnant mice, we demonstrate long-lasting transcriptional changes in fetal microglia that persist into postnatal life. We find that MIA induces widespread gene expression changes in neuronal and non-neuronal cells; importantly, these responses are abolished by selective genetic deletion of microglia, indicating that microglia are required for the transcriptional response of other cortical cell types to MIA. These findings demonstrate that microglia play a crucial durable role in the fetal response to maternal inflammation, and should be explored as potential therapeutic cell targets.

TAD evolutionary and functional characterization reveals diversity in mammalian TAD boundary properties and function

Topological associating domains (TADs) are self-interacting genomic units crucial for shaping gene regulation patterns. Despite their importance, the extent of their evolutionary conservation and its functional implications remain largely unknown. In this study, we generate Hi-C and ChIP-seq data and compare TAD organization across four primate and four rodent species and characterize the genetic and epigenetic properties of TAD boundaries in correspondence to their evolutionary conservation. We find 14% of all human TAD boundaries to be shared among all eight species (ultraconserved), while 15% are human-specific. Ultraconserved TAD boundaries have stronger insulation strength, CTCF binding, and enrichment of older retrotransposons compared to species-specific boundaries. CRISPR-Cas9 knockouts of an ultraconserved boundary in a mouse model lead to tissue-specific gene expression changes and morphological phenotypes. Deletion of a human-specific boundary near the autism-related AUTS2 gene results in the upregulation of this gene in neurons. Overall, our study provides pertinent TAD boundary evolutionary conservation annotations and showcases the functional importance of TAD evolution.

CRS: a circadian rhythm score model for predicting prognosis and treatment response in cancer patients

BACKGROUND

Circadian rhythm regulates complex physiological activities in organisms. A strong link between circadian dysfunction and cancer has been identified. However, the factors of dysregulation and functional significance of circadian rhythm genes in cancer have received little attention.

METHODS

In 18 cancer types from The Cancer Genome Atlas (TCGA), the differential expression and genetic variation of 48 circadian rhythm genes (CRGs) were examined. The circadian rhythm score (CRS) model was created using the ssGSEA method, and patients were divided into high and low groups based on the CRS. The Kaplan-Meier curve was created to assess the patient survival rate. Cibersort and estimate methods were used to identify the infiltration characteristics of immune cells between different CRS subgroups. Gene Expression Omnibus (GEO) dataset is used as verification queue and model stability evaluation queue. The CRS model's ability to predict chemotherapy and immunotherapy was assessed. Wilcoxon rank-sum test was used to compare the differences of CRS among different patients. We use CRS to identify potential "clock-drugs" by the connective map method.

RESULTS

Transcriptomic and genomic analyses of 48 CRGs revealed that most core clock genes are up-regulated, while clock control genes are down-regulated. Furthermore, we show that copy number variation may affect CRGs aberrations. Based on CRS, patients can be classified into two groups with significant differences in survival and immune cell infiltration. Further studies showed that patients with low CRS were more sensitive to chemotherapy and immunotherapy. Additionally, we identified 10 compounds (e.g. flubendazole, MLN-4924, ingenol) that are positively associated with CRS, and have the potential to modulate circadian rhythms.

CONCLUSIONS

CRS can be utilized as a clinical indicator to predict patient prognosis and responsiveness to therapy, and identify potential "clock-drugs".

TAD Evolutionary and functional characterization reveals diversity in mammalian TAD boundary properties and function

Topological associating domains (TADs) are self-interacting genomic units crucial for shaping gene regulation patterns. Despite their importance, the extent of their evolutionary conservation and its functional implications remain largely unknown. In this study, we generate Hi-C and ChIP-seq data and compare TAD organization across four primate and four rodent species, and characterize the genetic and epigenetic properties of TAD boundaries in correspondence to their evolutionary conservation. We find that only 14% of all human TAD boundaries are shared among all eight species (ultraconserved), while 15% are human-specific. Ultraconserved TAD boundaries have stronger insulation strength, CTCF binding, and enrichment of older retrotransposons, compared to species-specific boundaries. CRISPR-Cas9 knockouts of two ultraconserved boundaries in mouse models leads to tissue-specific gene expression changes and morphological phenotypes. Deletion of a human-specific boundary near the autism-related AUTS2 gene results in upregulation of this gene in neurons. Overall, our study provides pertinent TAD boundary evolutionary conservation annotations, and showcase the functional importance of TAD evolution.

Activity-Dependent Differential Regulation of Auts2 Isoforms In Vitro and In Vivo

Autism spectrum disorder (ASD) is a neurodevelopmental disorder of unknown cause, although one hypothesis suggests a potential imbalance between excitation and inhibition that leads to changes in neuronal activity and a disturbance in the brain network. However, the mechanisms through which neuronal activity contributes to the development of ASD remain largely unexplained. In this study, we described that neuronal activity at the transcriptional and translational levels regulated the expression of Auts2 isoforms. The prolonged stimulation of cultured cortical neurons significantly reduced the auts2 transcripts, accompanied by the decrease of FL-Auts2 protein, as well as one of the short isoforms (S-Auts2 var.1). Blocking neuronal activity increased the number of auts2 transcripts but not protein levels. Furthermore, blocking the NMDA receptors during stimulation could partially restore the FL-Auts2 and S-Auts2 var.1 at protein level, but not at mRNA level. Finally, Auts2 expression in the hippocampus was reduced in mice exposed to an enriched environment, a behavior paradigm designed to increase the brain activity through abundant sensory and social stimulations. Thus, our study revealed a novel regulatory effect of neuronal activity on the transcription and translation of ASD-risk gene auts2.

Epigenetic profile of Japanese supercentenarians: a cross-sectional study

BACKGROUND

Centenarians and supercentenarians with exceptional longevity are excellent models for research towards improvements of healthy life expectancy. Extensive research regarding the maintenance and reduction of epigenetic age has provided insights into increasing healthy longevity. To this end, we explored the epigenetic signatures reflecting hallmarks of exceptional healthy longevity, including avoidance of age-related diseases and cognitive functional decline.

METHODS

In this cross-sectional study, we enrolled Japanese non-centenarians (eligible participants aged 20-80 years) from the Tohoku Medical Megabank Community-Based Cohort Study and centenarians and supercentenarians (aged 101-115 years) from the Tokyo Centenarian Study and the Japanese Semi-supercentenarian Study. We assessed participants' whole-blood DNA methylation profiles and then developed sex-specific and non-specific first-generation epigenetic clocks by elastic net regression, calculated individuals' epigenetic ages, and assessed their age acceleration. We also screened for age-related CpG sites in non-centenarians by epigenome-wide linear regression analyses and ANOVA. We subsequently investigated which CpG sites in centenarians and supercentenarians had DNA methylation patterns following the age-related findings obtained from non-centenarians and which did not. We further characterised CpG sites with hypermethylation or hypomethylation in the centenarians and supercentenarians using enrichment and protein-protein interaction network analyses.

FINDINGS

We enrolled 421 non-centenarians (231 [55%] women and 190 [45%] men; age range 20-78 years), recruited between May 20, 2013, and March 31, 2016, and 94 centenarians and supercentenarians (66 women [70%] and 28 [30%] men; age range 101-115 years), recruited between Jan 20, 2001, and April 17, 2018. Non-sex-specific epigenetic clock showed the highest accuracy (r=0·96) based on which centenarians and supercentenarians had negative epigenetic age acceleration. Epigenome-wide association analyses further showed that centenarians and supercentenarians had younger-than-expected epigenetic states (DNA methylation profiles similar to those of non-centenarians) for 557 CpG sites enriched in cancer-related and neuropsychiatric-related genes, whereas these individuals had advanced (or older) epigenetic states for 163 CpG sites represented by genes related to TGF-β signalling, which is involved in anti-inflammatory responses and known to contribute to healthy ageing.

INTERPRETATION

These results indicate that exceptionally healthy longevity depends not only on maintaining young epigenetic states but also on advanced states of specific epigenetic regions.

FUNDING

The Japan Agency for Medical Research and Development, KDDI Research, and Keio University.

TRANSLATION

For the Japanese translation of the abstract see Supplementary Materials section.

auts2 Features and Expression Are Highly Conserved during Evolution Despite Different Evolutionary Fates Following Whole Genome Duplication

The AUTS2 gene plays major roles during brain development and is associated with various neuropathologies including autism. Data in non-mammalian species are scarce, and the aim of our study was to provide a comprehensive analysis of auts2 evolution in teleost fish, which are widely used for in vivo functional analysis and biomedical purposes. Comparative genomics in 78 species showed that auts2a and auts2b originate from the teleost-specific whole genome duplication (TGD). auts2a, which is highly similar to human AUTS2, was almost systematically retained following TGD. In contrast, auts2b, which encodes for a shorter protein similar to a short human AUTS2 isoform, was lost more frequently and independently during evolution. RNA-seq analysis in 10 species revealed a highly conserved profile with predominant expression of both genes in the embryo, brain, and gonads. Based on protein length, conserved domains, and expression profiles, we speculate that the long human isoform functions were retained by auts2a, while the short isoform functions were retained by auts2a and/or auts2b, depending on the lineage/species. auts2a showed a burst in expression during medaka brain formation, where it was expressed in areas of the brain associated with neurodevelopmental disorders. Together, our data suggest a strong conservation of auts2 functions in vertebrates despite different evolutionary scenarios in teleosts.

Comparing a Novel Malformation Syndrome Caused by Pathogenic Variants in FBRSL1 to AUTS2 Syndrome

Truncating variants in specific exons of Fibrosin-like protein 1 (FBRSL1) were recently reported to cause a novel malformation and intellectual disability syndrome. The clinical spectrum includes microcephaly, facial dysmorphism, cleft palate, skin creases, skeletal anomalies and contractures, postnatal growth retardation, global developmental delay as well as respiratory problems, hearing impairment and heart defects. The function of FBRSL1 is largely unknown, but pathogenic variants in the FBRSL1 paralog Autism Susceptibility Candidate 2 (AUTS2) are causative for an intellectual disability syndrome with microcephaly (AUTS2 syndrome). Some patients with AUTS2 syndrome also show additional symptoms like heart defects and contractures overlapping with the phenotype presented by patients with FBRSL1 mutations. For AUTS2, a dual function, depending on different isoforms, was described and suggested for FBRSL1. Both, nuclear FBRSL1 and AUTS2 are components of the Polycomb subcomplexes PRC1.3 and PRC1.5. These complexes have essential roles in developmental processes, cellular differentiation and proliferation by regulating gene expression via histone modification. In addition, cytoplasmic AUTS2 controls neural development, neuronal migration and neurite extension by regulating the cytoskeleton. Here, we review recent data on FBRSL1 in respect to previously published data on AUTS2 to gain further insights into its molecular function, its role in development as well as its impact on human genetics.