Mutations in the human NOTCH3 gene cause Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL). CADASIL is an inherited small vessel disease characterized by diverse clinical manifestations including vasculopathy, neurodegeneration, and dementia. Here we report two mutations in the zebrafish notch3 gene, one identified in a previous screen for mutations with reduced expression of myelin basic protein (mbp) and another caused by a retroviral insertion. Reduced mbp expression in embryos is associated with fewer oligodendrocyte precursor cells (OPCs) in notch3 mutants. Despite an early neurogenic phenotype, mbp expression recovered at later developmental stages and some of notch3 homozygous mutants survived to adulthood. Adult mutants for both notch3 alleles displayed a striking stress-associated accumulation of blood. Histological analysis of mutant vessels revealed vasculopathy, including an enlargement (dilation) of vessels in the telencephalon and fin, disorganization of the normal stereotyped arrangement of vessels in the fin, and an apparent loss of arterial morphological structure. Expression of hey1, a well-known transcriptional target of Notch signaling, was greatly reduced in notch3 mutants, suggesting Notch3 acts via a canonical Notch signaling pathway to promote normal vessel structure. Ultrastructural analysis confirmed the presence of dilated vessels in notch3 mutant fins and revealed that the vessel walls of presumed arteries showed signs of deterioration. Gaps evident in the arterial wall and the presence of blood cells outside of vessels in mutants indicated that compromised vessel structure led to hemorrhage. In notch3 heterozygotes, we found elevated expression of notch3 itself and target genes, indicating that specific alterations in gene expression caused by a partial loss of Notch3 function may contribute to pathologies observed in heterozygous larvae and adults. Our analysis of zebrafish notch3 mutants indicates that Notch3 regulates OPC development and mbp gene expression in larvae, and maintains vascular integrity in adults.
- Received February 3, 2013.
- Accepted May 22, 2013.
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