The homeodomain of Oct4 is a dimeric binder of methylated CpG elements

Epigenomic insights into common human disease pathology

The epigenome-the chemical modifications and chromatin-related packaging of the genome-enables the same genetic template to be activated or repressed in different cellular settings. This multi-layered mechanism facilitates cell-type specific function by setting the local sequence and 3D interactive activity level. Gene transcription is further modulated through the interplay with transcription factors and co-regulators. The human body requires this epigenomic apparatus to be precisely installed throughout development and then adequately maintained during the lifespan. The causal role of the epigenome in human pathology, beyond imprinting disorders and specific tumour suppressor genes, was further brought into the spotlight by large-scale sequencing projects identifying that mutations in epigenomic machinery genes could be critical drivers in both cancer and developmental disorders. Abrogation of this cellular mechanism is providing new molecular insights into pathogenesis. However, deciphering the full breadth and implications of these epigenomic changes remains challenging. Knowledge is accruing regarding disease mechanisms and clinical biomarkers, through pathogenically relevant and surrogate tissue analyses, respectively. Advances include consortia generated cell-type specific reference epigenomes, high-throughput DNA methylome association studies, as well as insights into ageing-related diseases from biological 'clocks' constructed by machine learning algorithms. Also, 3rd-generation sequencing is beginning to disentangle the complexity of genetic and DNA modification haplotypes. Cell-free DNA methylation as a cancer biomarker has clear clinical utility and further potential to assess organ damage across many disorders. Finally, molecular understanding of disease aetiology brings with it the opportunity for exact therapeutic alteration of the epigenome through CRISPR-activation or inhibition.

Pioneer factors: roles and their regulation in development

Pioneer factors are a subclass of transcription factors that can bind and initiate opening of silent chromatin regions. Pioneer factors subsequently regulate lineage-specific genes and enhancers and, thus, activate the zygotic genome after fertilization, guide cell fate transitions during development, and promote various forms of human cancers. As such, pioneer factors are useful in directed cell reprogramming. In this review, we define the structural and functional characteristics of pioneer factors, how they bind and initiate opening of closed chromatin regions, and the consequences for chromatin dynamics and gene expression during cell differentiation. We also discuss emerging mechanisms that modulate pioneer factors during development.

Transcriptional Coactivator BOB1 (OBF1, OCA-B) Modulates the Specificity of DNA Recognition by the POU-Domain Factors OCT1 and OCT2 in a Monomeric Configuration

BOB1, a mammalian lymphocyte-specific transcriptional coactivator of the transcription factors OCT1 and OCT2 (OCT1/2), plays important roles in normal immune responses, autoimmunity, and hematologic malignancies. The issue of a DNA sequence preference change imposed by BOB1 was raised more than two decades ago but remains unresolved. In this paper, using the EMSA-SELEX-Seq approach, we have reassessed the intrinsic ability of BOB1 to modulate the specificity of DNA recognition by OCT1 and OCT2. Our results have reaffirmed previous conclusions regarding BOB1 selectivity towards the dimer configuration of OCT1/2. However, they suggest that the monomeric configuration of these factors, assembled on the classical octamer ATGCAAAT and related motifs, are the primary targets of BOB1. Our data further specify the DNA sequence preference imposed by BOB1 and predict the probability of ternary complex formation. These results provide an additional insight into the action of BOB1-an essential immune regulator and a promising molecular target for the treatment of autoimmune diseases and hematologic malignancies.

Evaluation of the determinants for improved pluripotency induction and maintenance by engineered SOX17

An engineered SOX17 variant with point mutations within its DNA binding domain termed SOX17FNV is a more potent pluripotency inducer than SOX2, yet the underlying mechanism remains unclear. Although wild-type SOX17 was incapable of inducing pluripotency, SOX17FNV outperformed SOX2 in mouse and human pluripotency reprogramming. In embryonic stem cells, SOX17FNV could replace SOX2 to maintain pluripotency despite considerable sequence differences and upregulated genes expressed in cleavage-stage embryos. Mechanistically, SOX17FNV co-bound OCT4 more cooperatively than SOX2 in the context of the canonical SoxOct DNA element. SOX2, SOX17, and SOX17FNV were all able to bind nucleosome core particles in vitro, which is a prerequisite for pioneer transcription factors. Experiments using purified proteins and in cellular contexts showed that SOX17 variants phase-separated more efficiently than SOX2, suggesting an enhanced ability to self-organise. Systematic deletion analyses showed that the N-terminus of SOX17FNV was dispensable for its reprogramming activity. However, the C-terminus encodes essential domains indicating multivalent interactions that drive transactivation and reprogramming. We defined a minimal SOX17FNV (miniSOX) that can support reprogramming with high activity, reducing the payload of reprogramming cassettes. This study uncovers the mechanisms behind SOX17FNV-induced pluripotency and establishes engineered SOX factors as powerful cell engineering tools.