Role of m6A in Embryonic Stem Cell Differentiation and in Gametogenesis

The rising field of RNA modifications is stimulating massive research nowadays. m6A, the most abundant mRNA modification is highly conserved during evolution. Through the last decade, the essential components of this dynamic mRNA modification machinery were found and classified into writer, eraser and reader proteins. m6A modification is now known to take part in diverse biological processes such as embryonic development, cell circadian rhythms and cancer stem cell proliferation. In addition, there is already firm evidence for the importance of m6A modification in stem cell differentiation and gametogenesis, both in males and females. This review attempts to summarize the important results of recent years studying the mechanism underlying stem cell differentiation and gametogenesis processes

A Functional and Regulatory Map of Asthma

The prevalence and morbidity of asthma, a chronic inflammatory airway disease, is increasing. Animal models provide a meaningful but limited view of the mechanisms of asthma in humans. A systems-level view of asthma that integrates multiple levels of molecular and functional information is needed. For this, we compiled a gene expression compendium from five publicly available mouse microarray datasets and a gene knowledge base of 4,305 gene annotation sets. Using this collection we generated a high-level map of the functional themes that characterize animal models of asthma, dominated by innate and adaptive immune response. We used Module Networks analysis to identify co-regulated gene modules. The resulting modules reflect four distinct responses to treatment, including early response, general induction, repression, and IL-13–dependent response. One module with a persistent induction in response to treatment is mainly composed of genes with suggested roles in asthma, suggesting a similar role for other module members. Analysis of IL-13–dependent response using protein interaction networks highlights a role for TGF-β1 as a key regulator of asthma. Our analysis demonstrates the discovery potential of systems-level approaches and provides a framework for applying such approaches to asthma

Context-dependent functional compensation between Ythdf m6A reader proteins

The N6-methyladenosine (m6A) modification is the most prevalent post-transcriptional mRNA modification, regulating mRNA decay and splicing. It plays a major role during normal development, differentiation, and disease progression. The modification is regulated by a set of writer, eraser, and reader proteins. The YTH domain family of proteins consists of three homologous m6A-binding proteins, Ythdf1, Ythdf2, and Ythdf3, which were suggested to have different cellular functions. However, their sequence similarity and their tendency to bind the same targets suggest that they may have overlapping roles. We systematically knocked out (KO) the Mettl3 writer, each of the Ythdf readers, and the three readers together (triple-KO). We then estimated the effect in vivo in mouse gametogenesis, postnatal viability, and in vitro in mouse embryonic stem cells (mESCs). In gametogenesis, Mettl3-KO severity is increased as the deletion occurs earlier in the process, and Ythdf2 has a dominant role that cannot be compensated by Ythdf1 or Ythdf3, due to differences in readers' expression pattern across different cell types, both in quantity and in spatial location. Knocking out the three readers together and systematically testing viable offspring genotypes revealed a redundancy in the readers' role during early development that is Ythdf1/2/3 gene dosage-dependent. Finally, in mESCs there is compensation between the three Ythdf reader proteins, since the resistance to differentiate and the significant effect on mRNA decay occur only in the triple-KO cells and not in the single KOs. Thus, we suggest a new model for the Ythdf readers function, in which there is profound dosage-dependent redundancy when all three readers are equivalently coexpressed in the same cell types

Densely Interconnected Transcriptional Circuits Control Cell States in Human Hematopoiesis

Though many individual transcription factors are known to regulate hematopoietic differentiation, major aspects of the global architecture of hematopoiesis remain unknown. Here, we profiled gene expression in 38 distinct purified populations of human hematopoietic cells and used probabilistic models of gene expression and analysis of cis-elements in gene promoters to decipher the general organization of their regulatory circuitry. We identified modules of highly coexpressed genes, some of which are restricted to a single lineage but most of which are expressed at variable levels across multiple lineages. We found densely interconnected cis-regulatory circuits and a large number of transcription factors that are differentially expressed across hematopoietic states. These findings suggest a more complex regulatory system for hematopoiesis than previously assumed.National Institutes of Health (U.S.). Pioneer AwardBurroughs Wellcome Fund (Career Award at the Scientific Interface)Landon and Lavinia ClayHoward Hughes Medical Institut

Neutralizing Gatad2a-Chd4-Mbd3/NuRD Complex Facilitates Deterministic Induction of Naive Pluripotency

Mbd3, a member of nucleosome remodeling and deacetylase (NuRD) co-repressor complex, was previously identified as an inhibitor for deterministic induced pluripotent stem cell (iPSC) reprogramming, where up to 100% of donor cells successfully complete the process. NuRD can assume multiple mutually exclusive conformations, and it remains unclear whether this deterministic phenotype can be attributed to a specific Mbd3/NuRD subcomplex. More-over, since complete ablation of Mbd3 blocks somatic cell proliferation, we aimed to explore functionally relevant alternative ways to neutralize Mbd3-dependent NuRD activity. We identify Gatad2a, a NuRD-specific subunit, whose complete deletion specifically disrupts Mbd3/NuRD repressive activity on the pluripotency circuitry during iPSC differentiation and reprogramming without ablating somatic cell proliferation. Inhibition of Gatad2a facilitates deterministic murine iPSC reprogramming within 8 days. We validate a distinct molecular axis, Gatad2a-Chd4-Mbd3, within Mbd3/NuRD as being critical for blocking reestablishment of naive pluripotency and further highlight signaling-dependent and post-translational modifications of Mbd3/NuRD that influence its interactions and assembly

Densely Interconnected Transcriptional Circuits Control Cell States in Human Hematopoiesis

While many individual transcription factors are known to regulate hematopoietic differentiation, major aspects of the global architecture of hematopoiesis remain unknown. Here, we profiled gene expression in 38 distinct purified populations of human hematopoietic cells and used probabilistic models of gene expression and analysis of cis-elements in gene promoters to decipher the general organization of their regulatory circuitry. We identified modules of highly co-expressed genes, some of which are restricted to a single lineage, but most are expressed at variable levels across multiple lineages. We found densely interconnected cis-regulatory circuits and a large number of transcription factors that are differentially expressed across hematopoietic states. These findings suggest a more complex regulatory system for hematopoiesis than previously assumed