FOXA2 controls Pkd1l1 expression in the mouse node during left-right determination

Objectives

The embryonic node is a ciliated pit-like structure that is important in left-right (L-R) determination. Pkd1l1, encoding a membrane-bound ciliary protein, is expressed specifically in the node and is required to establish normal L-R patterning. Given the importance of this gene, we set out to understand its regulation.

Methods

Pkd1l1 and FoxA2 expression was compared through whole-mount in situ hybridization and β-galactosidase staining in 7.5-9.5 dpc mouse embryos. Bioinformatic analysis was used to characterise FOXA2 binding regions upstream of Pkd1l1 in the human-mouse lineage. Finally, luciferase assays were used to test the functionality of these potential regulatory regions.

Results

Our expression studies indicate that a regulatory relationship might exist between FOXA2 and Pkd1l1. Furthermore, Shh^-/- and FoxA2^c/c ;ShhcreER^T2 embryos display abnormal Pkd1l1 expression. Indeed, previous studies identified FOXA2 binding regions upstream of Pkd1l1, in both human and mouse. Our work has revealed the two regions to be non-homologous, but conserved in the human-mouse lineage, in some cases to the binding site level. Although bioinformatic analysis predicts lower binding affinities for the conserved mouse-identified region in human and vice versa, luciferase assays indicate that the conserved regions are capable of driving gene expression.

Conclusion

Our study implicates FOXA2 in the regulation of Pkd1l1 and characterises two FOXA2 binding regions upstream of this gene. Both regions are conserved across the human-mouse lineage to varying degrees. Furthermore, in both mouse and human, the two regions are able to activate gene expression.