A forward genetic screen identifies eukaryotic translation initiation factor 3, subunit H (eIF3h), as an enhancer of variegation in the mouse

Unveiling dysregulated lncRNAs and networks in non-syndromic cleft lip with or without cleft palate pathogenesis

Non-syndromic cleft lip with or without cleft palate (NSCL/P) is a common congenital facial malformation with a complex, incompletely understood origin. Long noncoding RNAs (lncRNAs) have emerged as pivotal regulators of gene expression, potentially shedding light on NSCL/P's etiology. This study aimed to identify critical lncRNAs and construct regulatory networks to unveil NSCL/P's underlying molecular mechanisms. Integrating gene expression profiles from the Gene Expression Omnibus (GEO) database, we pinpointed 30 dysregulated NSCL/P-associated lncRNAs. Subsequent analyses enabled the creation of competing endogenous RNA (ceRNA) networks, lncRNA-RNA binding protein (RBP) interaction networks, and lncRNA cis and trans regulation networks. RT-qPCR was used to examine the regulatory networks of lncRNA in vivo and in vitro. Furthermore, protein levels of lncRNA target genes were validated in human NSCL/P tissue samples and murine palatal shelves. Consequently, two lncRNAs and three mRNAs: FENDRR (log2FC = - 0.671, P = 0.040), TPT1-AS1 (log2FC = 0.854, P = 0.003), EIF3H (log2FC = - 1.081, P = 0.041), RBBP6 (log2FC = 0.914, P = 0.037), and SRSF1 (log2FC = 0.763, P = 0.026) emerged as potential contributors to NSCL/P pathogenesis. Functional enrichment analyses illuminated the biological functions and pathways associated with these lncRNA-related networks in NSCL/P. In summary, this study comprehensively delineates the dysregulated transcriptional landscape, identifies associated lncRNAs, and reveals pivotal sub-networks relevant to NSCL/P development, aiding our understanding of its molecular progression and setting the stage for further exploration of lncRNA and mRNA regulation in NSCL/P.

BAF complex-mediated chromatin relaxation is required for establishment of X chromosome inactivation

The process of epigenetic silencing, while fundamentally important, is not yet completely understood. Here we report a replenishable female mouse embryonic stem cell (mESC) system, Xmas, that allows rapid assessment of X chromosome inactivation (XCI), the epigenetic silencing mechanism of one of the two X chromosomes that enables dosage compensation in female mammals. Through a targeted genetic screen in differentiating Xmas mESCs, we reveal that the BAF complex is required to create nucleosome-depleted regions at promoters on the inactive X chromosome during the earliest stages of establishment of XCI. Without this action gene silencing fails. Xmas mESCs provide a tractable model for screen-based approaches that enable the discovery of unknown facets of the female-specific process of XCI and epigenetic silencing more broadly.

Female embryonic stem cells (ESCs) are the ideal model to study X chromosome inactivation (XCI) establishment; however, these cells are challenging to keep in culture. Here the authors create fluorescent ‘Xmas’ reporter mice as a renewable source of ESCs and show nucleosome remodelers Smarcc1 and Smarca4 create a nucleosome-free promoter region prior to the establishment of silencing.

Localization and Functional Roles of Components of the Translation Apparatus in the Eukaryotic Cell Nucleus

Components of the translation apparatus, including ribosomal proteins, have been found in cell nuclei in various organisms. Components of the translation apparatus are involved in various nuclear processes, particularly those associated with genome integrity control and the nuclear stages of gene expression, such as transcription, mRNA processing, and mRNA export. Components of the translation apparatus control intranuclear trafficking; the nuclear import and export of RNA and proteins; and regulate the activity, stability, and functional recruitment of nuclear proteins. The nuclear translocation of these components is often involved in the cell response to stimulation and stress, in addition to playing critical roles in oncogenesis and viral infection. Many components of the translation apparatus are moonlighting proteins, involved in integral cell stress response and coupling of gene expression subprocesses. Thus, this phenomenon represents a significant interest for both basic and applied molecular biology. Here, we provide an overview of the current data regarding the molecular functions of translation factors and ribosomal proteins in the cell nucleus.

Controlling tissue patterning by translational regulation of signaling transcripts through the core translation factor eIF3c

Although gene expression is tightly regulated during embryonic development, the impact of translational control has received less experimental attention. Here, we find that eukaryotic translation initiation factor-3 (eIF3) is required for Shh-mediated tissue patterning. Analysis of loss-of-function eIF3 subunit c (Eif3c) mice reveal a unique sensitivity to the Shh receptor patched 1 (Ptch1) dosage. Genome-wide in vivo enhanced cross-linking immunoprecipitation sequence (eCLIP-seq) shows unexpected specificity for eIF3 binding to a pyrimidine-rich motif present in subsets of 5'-UTRs and a corresponding change in the translation of these transcripts by ribosome profiling in Eif3c loss-of-function embryos. We further find a transcript specific effect in Eif3c loss-of-function embryos whereby translation of Ptch1 through this pyrimidine-rich motif is specifically sensitive to eIF3 amount. Altogether, this work uncovers hidden specificity of housekeeping translation initiation machinery for the translation of key developmental signaling transcripts.

Strain-Specific Epigenetic Regulation of Endogenous Retroviruses: The Role of Trans-Acting Modifiers

Approximately 10 percent of the mouse genome consists of endogenous retroviruses (ERVs), relics of ancient retroviral infections that are classified based on their relatedness to exogenous retroviral genera. Because of the ability of ERVs to retrotranspose, as well as their cis-acting regulatory potential due to functional elements located within the elements, mammalian ERVs are generally subject to epigenetic silencing by DNA methylation and repressive histone modifications. The mobilisation and expansion of ERV elements is strain-specific, leading to ERVs being highly polymorphic between inbred mouse strains, hinting at the possibility of the strain-specific regulation of ERVs. In this review, we describe the existing evidence of mouse strain-specific epigenetic control of ERVs and discuss the implications of differential ERV regulation on epigenetic inheritance models. We consider Krüppel-associated box domain (KRAB) zinc finger proteins as likely candidates for strain-specific ERV modifiers, drawing on insights gained from the study of the strain-specific behaviour of transgenes. We conclude by considering the coevolution of KRAB zinc finger proteins and actively transposing ERV elements, and highlight the importance of cross-strain studies in elucidating the mechanisms and consequences of strain-specific ERV regulation.

Metastable epialleles and their contribution to epigenetic inheritance in mammals

Many epigenetic differences between individuals are driven by genetic variation. Mammalian metastable epialleles are unusual in that they show variable DNA methylation states between genetically identical individuals. The occurrence of such states across generations has resulted in their consideration by many as strong evidence for epigenetic inheritance in mammals, with the classic A^vy and Axin^Fu mouse models - each products of repeat element insertions - being the most widely accepted examples. Equally, there has been interest in exploring their use as epigenetic biosensors given their susceptibility to environmental compromise. Here we review the classic murine metastable epialleles as well as more recently identified candidates, with the aim of providing a more holistic understanding of their biology. We consider the extent to which epigenetic inheritance occurs at metastable epialleles and explore the limited mechanistic insights into the establishment of their variable epigenetic states. We discuss their environmental modulation and their potential relevance in genome regulation. In light of recent whole-genome screens for novel metastable epialleles, we point out the need to reassess their biological relevance in multi-generational studies and we highlight their value as a model to study repeat element silencing as well as the mechanisms and consequences of mammalian epigenetic stochasticity.

The Genetics and Epigenetics of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, provides a powerful model of the complex interplay between genetic and epigenetic mechanisms of chromatin regulation. FSHD is caused by dysregulation of a macrosatellite repeat, either by contraction of the repeat or by mutations in silencing proteins. Both cases lead to chromatin relaxation and, in the context of a permissive allele, aberrant expression of the DUX4 gene in skeletal muscle. DUX4 is a pioneer transcription factor that activates a program of gene expression during early human development, after which its expression is silenced in most somatic cells. When misexpressed in FSHD skeletal muscle, the DUX4 program leads to accumulated muscle pathology. Epigenetic regulators of the disease locus represent particularly attractive therapeutic targets for FSHD, as many are not global modifiers of the genome, and altering their expression or activity should allow correction of the underlying defect.

Heterogeneity and specialized functions of translation machinery: from genes to organisms

Regulation of mRNA translation offers the opportunity to diversify the expression and abundance of proteins made from individual gene products in cells, tissues and organisms. Emerging evidence has highlighted variation in the composition and activity of several large, highly conserved translation complexes as a means to differentially control gene expression. Heterogeneity and specialized functions of individual components of the ribosome and of the translation initiation factor complexes eIF3 and eIF4F, which are required for recruitment of the ribosome to the mRNA 5' untranslated region, have been identified. In this Review, we summarize the evidence for selective mRNA translation by components of these macromolecular complexes as a means to dynamically control the translation of the proteome in time and space. We further discuss the implications of this form of gene expression regulation for a growing number of human genetic disorders associated with mutations in the translation machinery.

Eukaryotic translation initiation factor 3H suppression inhibits osteocarcinoma cell growth and tumorigenesis

Eukaryotic translation initiation factor 3H subunit (EIF3H) is a member of the EIF3 family and exhibits a central role in translation initiation in higher eukaryotes. Although EIF3H expression is upregulated in numerous tumour types, its potential role in human osteosarcoma (OS) has not yet been investigated. In the present study, it was demonstrated that EIF3H mRNA expression was upregulated in the human OS cell lines Saos-2 and U2OS. A recombinant lentivirus harbouring short hairpin RNA targeting EIF3H was constructed and successfully infected human OS Saos-2 and U2OS cells, resulting in 95% downregulated EIF3H expression compared with the respective control groups. Knockdown of EIF3H significantly inhibited the proliferation and colony formation of OS cells in vitro, and tumour growth in nude mice in vivo. Flow cytometry analysis revealed cell cycle arrest and promotion of apoptosis in OS cells with EIF3H knocked down. In conclusion, the results strongly suggested that EIF3H is a critical factor mediating the growth of OS cells and may represent a novel therapeutic target.

Panel sequencing of 264 candidate susceptibility genes and segregation analysis in a cohort of non-BRCA1, non-BRCA2 breast cancer families

PURPOSE

The main aim of this study was to screen epigenetic modifier genes and known breast cancer driver genes for germline mutations in non-BRCA1/2 (BRCAx) breast cancer families in order to identify novel susceptibility genes of moderate-high penetrance.

METHODS

We screened 264 candidate susceptibility genes in 656 index cases from non-BRCA1/2 families. Potentially pathogenic candidate mutations were then genotyped in all available family members for the assessment of co-segregation of the variant with disease in the family in order to estimate the breast cancer risks associated with these mutations. For 11 of the candidate susceptibility genes, we screened an additional 800 non-BRCA1/2 breast cancer cases and 787 controls.

RESULTS

Only two genes, CHD8 and USH2A showed any evidence of an increased risk of breast cancer (RR = 2.40 (95% CI 1.0-7.32) and 2.48 (95% CI 1.11-6.67), respectively).

CONCLUSIONS

We found no convincing evidence that epigenetic modifier and known breast cancer driver genes carry germline mutations that increase breast cancer risk. USH2A is no longer regarded as a breast cancer driver gene and seems an implausible candidate given its association with Usher syndrome. However, somatic mutations in CHD8 have been recently reported, making it an even more promising candidate, but further analysis of CHD8 in very large cohorts of families or case-control studies would be required to determine if it is a moderate-risk breast cancer susceptibility gene.

Translation Initiation Factors: Reprogramming Protein Synthesis in Cancer

Control of mRNA translation plays a crucial role in the regulation of gene expression and is critical for cellular homeostasis. Dysregulation of translation initiation factors has been documented in several pathologies including cancer. Aberrant function of translation initiation factors leads to translation reprogramming that promotes proliferation, survival, angiogenesis, and metastasis. In such context, understanding how altered levels (and presumably activity) of initiation factors can contribute to tumor initiation and/or maintenance is of major interest for the development of novel therapeutic strategies. In this review we provide an overview of translation initiation mechanisms and focus on recent findings describing the role of individual initiation factors and their aberrant activity in cancer.

Facioscapulohumeral muscular dystrophy as a model for epigenetic regulation and disease

SIGNIFICANCE

Aberrant epigenetic regulation is an integral aspect of many diseases and complex disorders. Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, is caused by disrupted genetic and epigenetic regulation of a macrosatellite repeat. FSHD provides a powerful model to investigate disease-relevant epigenetic modifiers and general mechanisms of epigenetic regulation that govern gene expression.

RECENT ADVANCES

In the context of a genetically permissive allele, the one aspect of FSHD that is consistent across all known cases is the aberrant epigenetic state of the disease locus. In addition, certain mutations in the chromatin regulator SMCHD1 (structural maintenance of chromosomes hinge-domain protein 1) are sufficient to cause FSHD2 and enhance disease severity in FSHD1. Thus, there are multiple pathways to generate the epigenetic dysregulation required for FSHD.

CRITICAL ISSUES

Why do some individuals with the genetic requirements for FSHD develop disease pathology, while others remain asymptomatic? Similarly, disease progression is highly variable among individuals. What are the relative contributions of genetic background and environmental factors in determining disease manifestation, progression, and severity in FSHD? What is the interplay between epigenetic factors regulating the disease locus and which, if any, are viable therapeutic targets?

FUTURE DIRECTIONS

Epigenetic regulation represents a potentially powerful therapeutic target for FSHD. Determining the epigenetic signatures that are predictive of disease severity and identifying the spectrum of disease modifiers in FSHD are vital to the development of effective therapies.

An ENU mutagenesis screen identifies novel and known genes involved in epigenetic processes in the mouse

Background

We have used a sensitized ENU mutagenesis screen to produce mouse lines that carry mutations in genes required for epigenetic regulation. We call these lines Modifiers of murine metastable epialleles (Mommes).

Results

We report a basic molecular and phenotypic characterization for twenty of the Momme mouse lines, and in each case we also identify the causative mutation. Three of the lines carry a mutation in a novel epigenetic modifier, Rearranged L-myc fusion (Rlf), and one gene, Rap-interacting factor 1 (Rif1), has not previously been reported to be involved in transcriptional regulation in mammals. Many of the other lines are novel alleles of known epigenetic regulators. For two genes, Rlf and Widely-interspaced zinc finger (Wiz), we describe the first mouse mutants. All of the Momme mutants show some degree of homozygous embryonic lethality, emphasizing the importance of epigenetic processes. The penetrance of lethality is incomplete in a number of cases. Similarly, abnormalities in phenotype seen in the heterozygous individuals of some lines occur with incomplete penetrance.

Conclusions

Recent advances in sequencing enhance the power of sensitized mutagenesis screens to identify the function of previously uncharacterized factors and to discover additional functions for previously characterized proteins. The observation of incomplete penetrance of phenotypes in these inbred mutant mice, at various stages of development, is of interest. Overall, the Momme collection of mouse mutants provides a valuable resource for researchers across many disciplines.

Translation factors and ribosomal proteins control tumor onset and progression: how?

Gene expression is shaped by translational control. The modalities and the extent by which translation factors modify gene expression have revealed therapeutic scenarios. For instance, eukaryotic initiation factor (eIF)4E activity is controlled by the signaling cascade of growth factors, and drives tumorigenesis by favoring the translation of specific mRNAs. Highly specific drugs target the activity of eIF4E. Indeed, the antitumor action of mTOR complex 1 (mTORc1) blockers like rapamycin relies on their capability to inhibit eIF4E assembly into functional eIF4F complexes. eIF4E biology, from its inception to recent pharmacological targeting, is proof-of-principle that translational control is druggable. The case for eIF4E is not isolated. The translational machinery is involved in the biology of cancer through many other mechanisms. First, untranslated sequences on mRNAs as well as noncoding RNAs regulate the translational efficiency of mRNAs that are central for tumor progression. Second, other initiation factors like eIF6 show a tumorigenic potential by acting downstream of oncogenic pathways. Third, genetic alterations in components of the translational apparatus underlie an entire class of inherited syndromes known as 'ribosomopathies' that are associated with increased cancer risk. Taken together, data suggest that in spite of their evolutionary conservation and ubiquitous nature, variations in the activity and levels of ribosomal proteins and translation factors generate highly specific effects. Beside, as the structures and biochemical activities of several noncoding RNAs and initiation factors are known, these factors may be amenable to rational pharmacological targeting. The future is to design highly specific drugs targeting the translational apparatus.

The use of mouse models to study epigenetics

Much of what we know about the role of epigenetics in the determination of phenotype has come from studies of inbred mice. Some unusual expression patterns arising from endogenous and transgenic murine alleles, such as the Agouti coat color alleles, have allowed the study of variegation, variable expressivity, transgenerational epigenetic inheritance, parent-of-origin effects, and position effects. These phenomena have taught us much about gene silencing and the probabilistic nature of epigenetic processes. Based on some of these alleles, large-scale mutagenesis screens have broadened our knowledge of epigenetic control by identifying and characterizing novel genes involved in these processes.

No evidence for cumulative effects in a Dnmt3b hypomorph across multiple generations

Observations of inherited phenotypes that cannot be explained solely through genetic inheritance are increasing. Evidence points to transmission of non-DNA molecules in the gamete as mediators of the phenotypes. However, in most cases it is unclear what the molecules are, with DNA methylation, chromatin proteins, and small RNAs being the most prominent candidates. From a screen to generate novel mouse mutants of genes involved in epigenetic reprogramming, we produced a DNA methyltransferase 3b allele that is missing exon 13. Mice that are homozygous for the mutant allele have smaller stature and reduced viability, with particularly high levels of female post-natal death. Reduced DNA methylation was also detected at telocentric repeats and the X-linked Hprt gene. However, none of the abnormal phenotypes or DNA methylation changes worsened with multiple generations of homozygous mutant inbreeding. This suggests that in our model the abnormalities are reset each generation and the processes of transgenerational epigenetic reprogramming are effective in preventing their inheritance.