| My thesis work has focused primarily on the characterization of two zebrafish mutations switch hitter (swt) and locke. Originally identified by a "curly tail" phenotype in a large scale mutagenesis screen, both mutants develop left-right patterning defects and renal cysts early during the zebrafish embryonic period. Zebrafish are an attractive model to study the earliest cellular defects occurring during renal cyst formation as its kidney (the pronephros) is simple and genes that cause cystic kidney diseases (CKD) in humans, cause pronephric dilations in zebrafish. By comparing phenotypes in three different mutants, locke, swt and kurly, we found that dilations occur in the medial tubules, a location similar to mammalian species. We show that phenotypes common to human CKD such an increased number of cells are secondary consequences of dilation and that the normally basolateral sodium/potassium ATPase is mislocalized. Cilia motility defects were the first observed phenotype in each mutant prior to nephron dilation. Although locke, swt and kurly show unique cilia defects, the cystic phenotypes are similar, suggesting a common cystogenesis pathway. Finally, we show that knock-down of polycystic kidney disease 2 (pkd2) specifically causes glomerular cysts and does not affect cilia motility. Based on these data, we were able to build a model describing primary versus secondary effects of CKD in zebrafish, and illustrate two distinctive types of pronephric cysts. Interestingly, switch hitter and locke mutants also display left-right organ patterning defects and function upstream of asymmetric gene expression. This intriguing link between left-right asymmetry defects and cystic kidneys is also observed in the mouse and in some cases of human disease. Recent research, including our own, has found that cilia are intimately involved in both processes. We have cloned the swt mutation to a gene coding for a novel Leucine rich repeat containing protein (Lrrc50) and the expression pattern correlates to tissues with motile cilia. Although locke has not been cloned, there are two interesting ciliary genes that make strong candidates. By studying these mutations in zebrafish, we aim to better access the genetic decisions that control proper organ patterning and renal tubular maintenance and the roles cilia play in these processes. |
