RFX2 is essential in the ciliated organ of asymmetry and an RFX2 transgene identifies a population of ciliated cells sufficient for fluid flow

Motile cilia create asymmetric fluid flow in the evolutionarily conserved ciliated organ of asymmetry (COA) and play a fundamental role in establishing the left–right (LR) axis in vertebrate embryos. The transcriptional control of the large group of genes that encode proteins that contribute to ciliary structure and function remains poorly understood. In this study we find that the winged helix transcription factor Rfx2 is expressed in motile cilia in mouse and zebrafish embryos. Morpholino knockdown of Rfx2 function in the whole embryo or specifically in cells of the zebrafish COA (Kupffer's Vesicle, KV) leads to reduced KV cilia length and perturbations in LR asymmetry. LR patterning defects include randomization of the early asymmetric Nodal signaling pathway genes southpaw, lefty1 and lefty2 and subsequent reversals in the organ primordia of the heart and gut. Rfx2 is also required for ciliogenesis in zebrafish pronephric duct. We further show that by restoring Left–Right dynein (LRD) expression and motility specifically in a subset of ciliated cells of the mouse COA (posterior notochord, PNC), we can restore fluid flow, asymmetric expression of Pitx2 and partially rescue situs defects.