Using zebrafish as a model for a rare kidney disease

Abstract

Several inherited diseases are characterized by the combination of hearing loss with kidney problems highlighting a group of genes involved the development and function of both organs. The work presented in this thesis concerns a yet undescribed inherited disease which affects these two organs. Patients from the Druze group were found to have sensorineural hearing loss in the high frequency range and proteinuria. Subsequent investigations revealed high urinary levels of beta-2-microglobulin and poor renal accumulation of Tc-99m DMSA (dimercaptosuccinic acid) despite a normal glomerular filtration rate. This suggested a defect in proximal tubular function. These symptoms did not match any current diseases but suggested an unrecognised novel disorder. Genetic studies revealed an underlying mutation in the gene EHD1 in affected individuals. The key aim was to better understand the function of EHD1. To do so, we aimed to study a zebrafish knockout line as a model and identified ehd1a as the closest candidate. We obtained an existing ehd1a knockout mutant line which predicted the insertion in an intron of ehd1a. Yet, with the subsequent update of the zebrafish genome assembly, investigations into the mutant line revealed that this intronic sequence belonged to another gene, fam210aa. We therefore aimed to develop a new ehd1a mutant line via the use of CRISPR technology, which I successfully generated. I assessed the functionality of the equivalent of the proximal tubules in these zebrafish in comparison to wild type using a small molecular tracer, that is normally endocytosed by the tubule. After injecting this tracer into the ehd1a-/- mutants, wildtype and heterozygous siblings, there was no significant difference between these groups in uptake, suggesting that either the zebrafish orthologue has a different function than in man, or that ehd1a is not the functional orthologue and possibly other family members may be the key to elucidating the physiology behind the phenotype in this proximal tubulopathy