32 PKD2 mutant zebrafish display excessive developmental angiogenesis

Rationale Mutations in the PKD2 gene cause human autosomal dominant polycystic kidney disease (ADPKD). ADPKD is associated with vascular complications independent of renal dysfunction but little is known about the role of PKD2 in vascular development. We therefore characterised vascular development in PKD2 mutant zebrafish.

Methodology We identified a novel PKD2 mutant zebrafish generated in a previously unpublished N-ethyl-N-nitrosourea mutagenesis screen. This was crossed with endothelial transgenic lines fli1:EGFP (cytoplasmic GFP) and flk1:nlsEGFP (nuclear localised GFP). Serial confocal microscopy was used to image the developing vasculature of PKD2 mutants and wildtype siblings until 5-day old. Mutant embryos were stained with phalloidin that labels muscle cells.

Results Genotyping revealed the PKD2 mutation to be g.5860G>A, leading to a premature stop codon in exon 5. As described for other zebrafish PKD2 mutant alleles, homozygous mutants had a pronounced dorsal curvature but otherwise developed normally with no delay in onset of circulation. When we quantified endothelial number in the intersomitic vessels (ISVs) running between the somites we found this was almost doubled in PKD2 mutants by 3-day old (p<0.001) and persisted until at least 5-day old. When we characterised ISV morphology, we observed highly abnormal loops that were never observed in wildtypes. Phalloidin staining showed no alteration in somite structure to account for abnormal ISV patterning.

Conclusion This is the first description of hyperproliferative angiogenesis induced by mutations in PKD2. The mechanism needs to be further delineated but our data suggest abnormal vessel development may underlie some vascular complications of ADPKD.