Loss of a cilia-associated gene, pkd1l1, causes biliary defects in zebrafish: Implications for Biliary Atresia Splenic Malformation.

Biliary atresia (BA) is a fibroinflammatory neonatal disease with no effective therapies. A subset of cases (10-20%), are associated with laterality defects - BA Splenic Malformation (BASM) syndrome. Recently, whole exome sequencing of BASM patients identified deleterious variants in PKD1L1. PKD1L1 is involved in L-R axis determination, however its role in cholangiocytes is unknown. We generated the pkd1l1hsc117 allele using CRISPR/Cas9 mutagenesis in zebrafish to determine the role of Pkd1l1 in biliary development and function. Wild type (WT) and mutant larvae were assessed for laterality defects, biliary function and biliary tree architecture in 5-day- post-fertilization embryos. pkd1l1hsc117 mutant larvae exhibit early left-right patterning defects. The gallbladder was positioned on the left in 47% of mutants compared to 4% in WT larvae. PED6 accumulation was significantly reduced in pkd1l1hsc117 mutants (46%) compared to WT (4%). pkd1l1hsc117 exhibited fewer biliary epithelial cells and reduced density of the intrahepatic biliary network compared to WT. These data highlight the essential role of pkd1l1 in normal development and function of the zebrafish biliary system, supporting a role for this gene as a cause for BASM.