Functional mechanisms of MYRF DNA-binding domain mutations implicated in birth defects

Splicing variants in MYRF cause partial loss of function in the retinal pigment epithelium

Myelin Regulatory Factor (MYRF) regulates retinal pigment epithelial (RPE) development and variants in the C-terminus are linked to isolated nanophthalmos, while loss-of-function variants cause syndromic disease. To define the molecular mechanism of this discrepancy, in vitro and animal studies were performed on a pathogenic C-terminal variant (p.Gly1126fs30* or dG-MYRF). ARPE-19 cells transduced with dG-MYRF revealed reduced target gene expression compared to WT-MYRF, with reduced steady state levels of C-terminal MYRF cleavage product, but intact cleavage and localization. A homozygous humanized MYRF C-terminal ( Myrf humdG/humdG ) mouse model was embryonic lethal by embryonic day (E) 18.5, while humanized wildtype ( Myrf humWT/humWT ) showed normal expression and survival. Bioinformatic analysis on integrated single cell RNA-seq from humanized E17.5 and knockout Rx-Cre;Myrf fl/fl (E15.5 and P0) mice supported shared differentially expressed genes with decreased effect size in Myrf humdG/humdG eyes. These findings, and the viability differences, support that dG-MYRF is a hypomorphic allele. Further, two novel MYRF splicing variants were identified in families with isolated nanophthalmos, with one confirmed to alter 40% of spliced transcripts, creating a nonfunctional isoform. These cases corroborate that isolated nanophthalmos results from hypomorphic alleles of MYRF, supporting a tissue-specific threshold effect and suggests that the C-terminus has unique roles in the RPE.

Anomalous Left Coronary Artery from the Pulmonary Artery in Three Patients with MYRF-Associated Cardiac-Urogenital Syndrome

Cardiac-Urogenital Syndrome (CUGS) is a recently identified genetic disease characterized by urogenital, diaphragmatic, ophthalmic, and cardiac abnormalities caused by heterozygous pathogenic variants in the Myelin Regulatory Factor (MYRF) gene. The complete spectrum of disease characteristics and prevalence is not yet defined. This report documents the first known cases of anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) in MYRF-associated Cardiac-Urogenital Syndrome (MYRF-CUGS).

MYRF: A unique transmembrane transcription factor- from proteolytic self-processing to its multifaceted roles in animal development

The Myelin Regulator Factor (MYRF) is a master regulator governing myelin formation and maintenance in the central nervous system. The conservation of MYRF across metazoans and its broad tissue expression suggest it has functions extending beyond the well-established role in myelination. Loss of MYRF results in developmental lethality in both invertebrates and vertebrates, and MYRF haploinsufficiency in humans causes MYRF-related Cardiac Urogenital Syndrome, underscoring its importance in animal development; however, these mechanisms are largely unexplored. MYRF, an unconventional transcription factor, begins embedded in the membrane and undergoes intramolecular chaperone mediated trimerization, which triggers self-cleavage, allowing its N-terminal segment with an Ig-fold DNA-binding domain to enter the nucleus for transcriptional regulation. Recent research suggests developmental regulation of cleavage, yet the mechanisms remain enigmatic. While some parts of MYRF's structure have been elucidated, others remain obscure, leaving questions about how these motifs are linked to its intricate processing and function.

MYRF-related mild encephalopathy with reversible myelin vacuolization: a case report and literature review

Background: MYRF-related mild encephalopathy with reversible myelin vacuolization (MMERV) is an inherited neurological disorder characterized by dysfunction in the central nervous system and widespread reversible leukoencephalopathy. This paper presents a confirmed case of familial MMERV and summarizes pertinent features to offer guidance for future diagnosis and treatment of MMERV. Case Introduction: We have diagnosed a case of MMERV based on a history of seizures during early childhood and recurrent speech fluency issues in adulthood, reversible abnormal intensities in bilateral white matter in the centrum semiovale and corpus callosum, and the identification of myelin regulatory factor (MYRF) heterozygous variants. Conclusion: MYRF-related mild encephalopathy with reversible myelin vacuolization is a rare autosomal dominant genetic disease, with early clinical manifestations often being seizures. The definitive diagnosis of MMERV can be confirmed through genetic analysis. Minimizing infections can help reduce disease recurrence. However, future research should explore the impact of MYRF heterozygous variants in the wider MMERV population.

Uncovering oligodendrocyte enhancers that control Cnp expression

Oligodendrocytes (OLs) produce myelin sheaths around axons in the central nervous system (CNS). Myelin accelerates the propagation of action potentials along axons and supports the integrity of axons. Impaired myelination has been linked to neurological and neuropsychiatric disorders. As a major component of CNS myelin, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) plays an indispensable role in the axon-supportive function of myelin. Notably, this function requires a high-level expression of CNP in OLs, as evidenced by downregulated expression of CNP in mental disorders and animal models. Little is known about how CNP expression is regulated in OLs. Especially, OL enhancers that govern CNP remain elusive. We have recently developed a powerful method that links OL enhancers to target genes in a principled manner. Here, we applied it to Cnp, uncovering two OL enhancers for it (termed Cnp-E1 and Cnp-E2). Epigenome editing analysis revealed that Cnp-E1 and Cnp-E2 are dedicated to Cnp. ATAC-seq and ChIP-seq data show that Cnp-E1 and Cnp-E2 are conserved OL-specific enhancers. Single cell multi-omics data that jointly profile gene expression and chromatin accessibility suggest that Cnp-E2 plays an important role in Cnp expression in the early stage of OL differentiation while Cnp-E1 sustains it in mature OLs.

Hypoplastic Left Heart Syndrome: Signaling & Molecular Perspectives, and the Road Ahead

Hypoplastic left heart syndrome (HLHS) is a lethal congenital heart disease (CHD) affecting 8-25 per 100,000 neonates globally. Clinical interventions, primarily surgical, have improved the life expectancy of the affected subjects substantially over the years. However, the etiological basis of HLHS remains fundamentally unclear to this day. Based upon the existing paradigm of studies, HLHS exhibits a multifactorial mode of etiology mediated by a complicated course of genetic and signaling cascade. This review presents a detailed outline of the HLHS phenotype, the prenatal and postnatal risks, and the signaling and molecular mechanisms driving HLHS pathogenesis. The review discusses the potential limitations and future perspectives of studies that can be undertaken to address the existing scientific gap. Mechanistic studies to explain HLHS etiology will potentially elucidate novel druggable targets and empower the development of therapeutic regimens against HLHS in the future.

CRISPR-based knockout and base editing confirm the role of MYRF in heart development and congenital heart disease

High-throughput DNA sequencing studies increasingly associate DNA variants with congenital heart disease (CHD). However, functional modeling is a crucial prerequisite for translating genomic data into clinical care. We used CRISPR-Cas9-mediated targeting of 12 candidate genes in the vertebrate model medaka (Oryzias latipes), five of which displayed a novel cardiovascular phenotype spectrum in F0 (crispants): mapre2, smg7, cdc42bpab, ankrd11 and myrf, encoding a transcription factor recently linked to cardiac-urogenital syndrome. Our myrf mutant line showed particularly prominent embryonic cardiac defects recapitulating phenotypes of pediatric patients, including hypoplastic ventricle. Mimicking human mutations, we edited three sites to generate specific myrf single-nucleotide variants via cytosine and adenine base editors. The Glu749Lys missense mutation in the conserved intramolecular chaperon autocleavage domain fully recapitulated the characteristic myrf mutant phenotype with high penetrance, underlining the crucial function of this protein domain. The efficiency and scalability of base editing to model specific point mutations accelerate gene validation studies and the generation of human-relevant disease models.

A Glance at the Molecules That Regulate Oligodendrocyte Myelination

Oligodendrocyte (OL) myelination is a critical process for the neuronal axon function in the central nervous system. After demyelination occurs because of pathophysiology, remyelination makes repairs similar to myelination. Proliferation and differentiation are the two main stages in OL myelination, and most factors commonly play converse roles in these two stages, except for a few factors and signaling pathways, such as OLIG2 (Oligodendrocyte transcription factor 2). Moreover, some OL maturation gene mutations induce hypomyelination or hypermyelination without an obvious function in proliferation and differentiation. Herein, three types of factors regulating myelination are reviewed in sequence.

Identifying oligodendrocyte enhancers governing Plp1 expression

Oligodendrocytes (OLs) produce myelin in the central nervous system (CNS), which accelerates the propagation of action potentials and supports axonal integrity. As a major component of CNS myelin, proteolipid protein 1 (Plp1) is indispensable for the axon-supportive function of myelin. Notably, this function requires the continuous high-level expression of Plp1 in OLs. Equally important is the controlled expression of Plp1, as illustrated by Pelizaeus-Merzbacher disease for which the most common cause is PLP1 overexpression. Despite a decade-long search, promoter-distal OL enhancers that govern Plp1 remain elusive. We have recently developed an innovative method that maps promoter-distal enhancers to genes in a principled manner. Here, we applied it to Plp1, uncovering two OL enhancers for it (termed Plp1-E1 and Plp1-E2). Remarkably, clustered regularly interspaced short palindromic repeats (CRISPR) interference epigenome editing showed that Plp1-E1 and Plp1-E2 do not regulate two genes in their vicinity, highlighting their exquisite specificity to Plp1. Assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and chromatin immunoprecipitation with high-throughput sequencing (ChIP-seq) data show that Plp1-E1 and Plp1-E2 are OL-specific enhancers that are conserved among human, mouse and rat. Hi-C data reveal that the physical interactions between Plp1-E1/2 and PLP1 are among the strongest in OLs and specific to OLs. We also show that Myrf, a master regulator of OL development, acts on Plp1-E1 and Plp1-E2 to promote Plp1 expression.