DYX1C1, DCDC2, and KIAA0319 are
three of the most replicated dyslexia candidate genes (DCGs). Recently, these DCGs
were implicated in functions at the cilium. Here, we investigate the regulation of
these DCGs by Regulatory Factor X transcription factors (RFX TFs), a gene family
known for transcriptionally regulating ciliary genes. We identify conserved X-box
motifs in the promoter regions of DYX1C1, DCDC2, and
KIAA0319 and demonstrate their functionality, as well as the
ability to recruit RFX TFs using reporter gene and electrophoretic mobility shift
assays. Furthermore, we uncover a complex regulation pattern between
RFX1, RFX2, and RFX3 and their
significant effect on modifying the endogenous expression of DYX1C1
and DCDC2 in a human retinal pigmented epithelial cell line
immortalized with hTERT (hTERT-RPE1). In addition, induction of ciliogenesis
increases the expression of RFX TFs and DCGs. At the protein level, we show that
endogenous DYX1C1 localizes to the base of the cilium, whereas DCDC2 localizes along
the entire axoneme of the cilium, thereby validating earlier localization studies
using overexpression models. Our results corroborate the emerging role of DCGs in
ciliary function and characterize functional noncoding elements, X-box promoter
motifs, in DCG promoter regions, which thus can be targeted for mutation screening in
dyslexia and ciliopathies associated with these genes.—Tammimies, K., Bieder,
A., Lauter, G., Sugiaman-Trapman, D., Torchet, R., Hokkanen, M.-E., Burghoorn, J.,
Castrén, E., Kere, J., Tapia-Páez, I., Swoboda, P. Ciliary dyslexia
candidate genes DYX1C1 and DCDC2 are regulated by
Regulatory Factor (RF) X transcription factors through X-box promoter motifs.