Evolutionary diversification of RFX family genes as master regulators of ciliogenesis

Abstract

After originally proposed by Susumu Ohno 50 years ago, ‘Evolution by Gene Duplication’ and the gene functional diversification after the event have been considered the central mechanism for how the species can expand their gene repertoires during the evolution. The transcriptional regulator RFX (regulatory factor X) gene family is conserved across taxa and characterized their roles in the ciliogenesis in multiple models, such as worm, fly, zebrafish, Xenopus, mouse, and human. But the functions of each member in the family in various multiciliated tissues are still intriguing. For a better understanding of functional diversification, we investigated the ancient form of RFX family members. Only a single RFX ortholog is available in the fruitfly and worm, so we tested whether it has the conserved transcriptional regulatory function in ciliogenesis. Surprisingly, fly Rfx can complement the Xenopus Rfx2 protein in the ciliogenesis of MCC. We investigated the DNA binding sites of fly, Xenopus, and human orthologous genes using ChIP-seq experiments and analyzed the difference among their binding motifs and target genes. Furthermore, we further examined the cell-type specificity of these specific and common target genes of multiple Rfx gene family members by analyzing the public single-cell transcriptome data of ependymal, fallopian tubes, and airway mucociliary epithelium. This result will provide new insight into the functional conservation and diversification of the RFX gene family in ciliogenesis.