👤 Calum MacRae

TF (transcription factor) Prdm16 (positive regulatory domain-containing protein 16) regulates hematopoietic and neuronal stem cell homeostasis, adipose differentiation, and cardiac development. Its role in the circulatory system extends beyond the heart, as Prdm16 loss in arterial endothelial cells (ECs) impairs arterial reperfusion of ischemic mouse limbs due to endothelial dysfunction, and Zebrafish were used to analyze vascular development, arteriovenous endothelial specification, and the emergence of arteriovenous malformations in the absence or presence of Prdm16 or Notch signaling. Lentiviral-mediated Prdm16 overexpression in human endothelial (progenitor) cells was coupled to qRT-PCR (real-time quantitative polymerase chain reaction), Western blot, and transcriptional profiling to document Prdm16's importance for arterial lineage specification. Coimmunoprecipitation in HEK293 (human embryonic kidney 293) cells was performed to assess physical interaction between Prdm16 and the Notch pathway. Existing mouse and human data sets were reanalyzed to evaluate Prdm16 expression in mammalian arteriovenous malformations. Prdm16 actively promotes arterial EC identity while suppressing venous fate. Like in mice, Prdm16 is expressed by arterial ECs early during vascular development in zebrafish, where it synergistically coordinates arterial development together with canonical notch signaling, as their combined loss in zebrafish leads to arteriovenous malformations. PRDM16's arterializing effect on human ECs is dependent on canonical Notch activity, as it is blunted in the presence of canonical Notch inhibitors and potentiated in the presence of delta-like ligand 4. Mechanistically, Prdm16 does not increase the protein levels of the cleaved intracellular domain of Notch receptors (notch intracellular domain) but rather potentiates the effect of the latter via physical and functional interaction. Prdm16 further finetunes Notch signaling and arterial development by complexing with Hey2 (Hes-related family bHLH TF with YRPW motif 2), the basic helix-loop-helix TF acting downstream of canonical Notch during arterial lineage specification and development. Together, our data demonstrate an intricate interplay between Prdm16 and Notch in ECs and indicate that Prdm16 signaling may constitute a novel therapeutic target for arteriovenous malformations. Show less

An estimated 1 in 500 people live with hypertrophic cardiomyopathy (HCM), a disease for which genetic diagnosis can identify family members at risk, and increasingly guide therapy. Mutations in the myosin binding protein C3 ( We developed a scaled multidimensional mapping strategy to evaluate the functional impact of variants across a critical domain of MYBPC3. We incorporate saturation base editing at the native Our multidimensional mapping strategy enabled high-resolution functional analysis of This work provides a platform for extending genome engineering in iPSCs to multiplexed assays of variant effects across diverse disease-relevant cellular phenotypes, enhancing the understanding of variant pathogenicity and uncovering novel biological mechanisms that could inform therapeutic strategies. Show less

RBPs (RNA-binding proteins) perform indispensable functions in the post-transcriptional regulation of gene expression. Numerous RBPs have been implicated in cardiac development or physiology based on gene knockout studies and the identification of pathogenic RBP gene mutations in monogenic heart disorders. The discovery and characterization of additional RBPs performing indispensable functions in the heart will advance basic and translational cardiovascular research. We performed a differential expression screen in zebrafish embryos to identify genes enriched in We identified 1848 genes enriched in the Our study identifies Show less

As DNA sequencing costs decline, genetic testing options have expanded. Whole exome sequencing and whole genome sequencing (WGS) are entering clinical use, posing questions about their incremental value compared with disease-specific multigene panels that have been the cornerstone of genetic testing. Forty-one patients with hypertrophic cardiomyopathy who had undergone targeted hypertrophic cardiomyopathy genetic testing (either multigene panel or familial variant test) were recruited into the MedSeq Project, a clinical trial of WGS. Results from panel genetic testing and WGS were compared. In 20 of 41 participants, panel genetic testing identified variants classified as pathogenic, likely pathogenic, or uncertain significance. WGS identified 19 of these 20 variants, but the variant detection algorithm missed a pathogenic 18 bp duplication in myosin binding protein C ( WGS detected nearly all variants identified on panel testing, provided 1 new diagnostic finding, and allowed interrogation of posited disease genes. Several variants of uncertain clinical use and numerous secondary genetic findings were also identified. Whereas panel testing and WGS provided similar diagnostic yield, WGS offers the advantage of reanalysis over time to incorporate advances in knowledge, but requires expertise in genomic interpretation to appropriately incorporate WGS into clinical care. URL: https://clinicaltrials.gov. Unique identifier: NCT01736566. Show less

Genetic variants that cause haploinsufficiency account for many autosomal dominant (AD) disorders. Gene-based diagnosis classifies variants that alter canonical splice signals as pathogenic, but due to imperfect understanding of RNA splice signals other variants that may create or eliminate splice sites are often clinically classified as variants of unknown significance (VUS). To improve recognition of pathogenic splice-altering variants in AD disorders, we used computational tools to prioritize VUS and developed a cell-based minigene splicing assay to confirm aberrant splicing. Using this two-step procedure we evaluated all rare variants in two AD cardiomyopathy genes, lamin A/C ( Show less

Conventional drug discovery approaches require a priori selection of an appropriate molecular target, but it is often not obvious which biological pathways must be targeted to reverse a disease phenotype. Phenotype-based screens offer the potential to identify pathways and potential therapies that influence disease processes. The zebrafish mutation gridlock (grl, affecting the gene hey2) disrupts aortic blood flow in a region and physiological manner akin to aortic coarctation in humans. Here we use a whole-organism, phenotype-based, small-molecule screen to discover a class of compounds that suppress the coarctation phenotype and permit survival to adulthood. These compounds function during the specification and migration of angioblasts. They act to upregulate expression of vascular endothelial growth factor (VEGF), and the activation of the VEGF pathway is sufficient to suppress the gridlock phenotype. Thus, organism-based screens allow the discovery of small molecules that ameliorate complex dysmorphic syndromes even without targeting the affected gene directly. Show less