Jonathan M. Skarie

The Primary open-angle glaucoma gene WDR36 functions in ribosomal RNA processing and interacts with the p53 stress–response pathway

Primary open-angle glaucoma (POAG) is a genetically complex neuropathy that affects retinal ganglion cells and is a leading cause of blindness worldwide. WDR36, a gene of unknown function, was recently identified as causative for POAG at locus GLC1G. Subsequent studies found disease-associated variants in control populations, leaving the role of WDR36 in this disease unclear. To address this issue, we determined the function of WDR36. We studied Wdr36 in zebrafish and found it is the functional homolog of yeast Utp21. Utp21 is cell essential and functions in the nucleolar processing of 18S rRNA, which is required for ribosome biogenesis. Evidence for functional homology comes from sequence alignment, ubiquitous expression, sub-cellular localization to the nucleolus and loss-of-function phenotypes that include defects in 18S rRNA processing and abnormal nucleolar morphology. Additionally, we show that loss of Wdr36 function leads to an activation of the p53 stress-response pathway, suggesting that co-inheritance of defects in p53 pathway genes may influence the impact of WDR36 variants on POAG. Although these results overall do not provide evidence for or against a role of WDR36 in POAG, they do provide important baseline information for future studies.

FoxC1 Is Essential for Vascular Basement Membrane Integrity and Hyaloid Vessel Morphogenesis

PURPOSE Alterations in FOXC1 dosage lead to a spectrum of highly penetrant, ocular anterior segment dysgenesis phenotypes. The most serious outcome is the development of glaucoma, which occurs in 50% to 75% of patients. Therefore, the need to identify specific pathways and genes that interact with FOXC1 to promote glaucoma is great. In this study, the authors investigated the loss of foxC1 in the zebrafish to characterize phenotypes and gene interactions that may impact glaucoma pathogenesis. METHODS Morpholino knockdown in zebrafish, RNA and protein marker analyses, transgenic reporter lines, and angiography, along with histology and transmission electron microscopy, were used to study foxC1 function and gene interactions. RESULTS Zebrafish foxC1 genes were expressed dynamically in the developing vasculature and periocular mesenchyme during development. Multiple ocular and vascular defects were found after the knockdown of foxC1. Defects in the hyaloid vasculature, arteriovenous malformations, and coarctation of the aorta were observed with maximal depletion of foxC1. Partial loss of foxC1 resulted in CNS and ocular hemorrhages, defects in intersegmental vessel patterning, and increased vascular permeability. To investigate the basis for these disruptions, the ultrastructure of foxC1-depleted hyaloid vascular cells was studied. These experiments, along with laminin-111 immunoreactivity, revealed disruptions in basement membrane integrity. Finally, codepletion of laminin alpha-1 and foxC1 uncovered a genetic interaction between these genes during development. CONCLUSIONS Genetic interactions between FOXC1 and basement membrane components influence vascular stability and may impact glaucoma development and increase stroke risk in FOXC1 patients.

Mutation of FOXC1 and PITX2 induces cerebral small-vessel disease

Patients with cerebral small-vessel disease (CSVD) exhibit perturbed end-artery function and have an increased risk for stroke and age-related cognitive decline. Here, we used targeted genome-wide association (GWA) analysis and defined a CSVD locus adjacent to the forkhead transcription factor FOXC1. Moreover, we determined that the linked SNPs influence FOXC1 transcript levels and demonstrated that patients as young as 1 year of age with altered FOXC1 function exhibit CSVD. MRI analysis of patients with missense and nonsense mutations as well as FOXC1-encompassing segmental duplication and deletion revealed white matter hyperintensities, dilated perivascular spaces, and lacunar infarction. In a zebrafish model, overexpression or morpholino-induced suppression of foxc1 induced cerebral hemorrhage. Inhibition of foxc1 perturbed platelet-derived growth factor (Pdgf) signaling, impairing neural crest migration and the recruitment of mural cells, which are essential for vascular stability. GWA analysis also linked the FOXC1-interacting transcription factor PITX2 to CSVD, and both patients with PITX2 mutations and murine Pitx2-/- mutants displayed brain vascular phenotypes. Together, these results extend the genetic etiology of stroke and demonstrate an increasing developmental basis for human cerebrovascular disease.