Control of axonemal proximodistal patterning by the small GTPase Rsg1. (a-a”) A representative Xenopus multiciliated cell (MCC), co-expressing GFP-MAP7, a marker of proximal ciliary identity, and RFP-CLAMP, a marker of the distal-tips of cilia. (b-b”) A MCC co-expressing GFP-MAP7 and RFP-CLAMP, and in which the function of the small GTPase, Rsg1, has been knocked-down (KD) by a translation-blocking antisense morpholino oligonucleotide. Note the significantly shortened or absent distal compartments of RFP-CLAMP as compared to controls. In addition, the proximal compartment marked by GFP-MAP7 is significantly expanded in these axonemes. This cell exhibits a moderate Rsg1 KD phenotype, and was chosen to facilitate direct comparison with the control cell. (c) Quantification of axonemal RFP-CLAMP compartments reveals a severe reduction in distal identity upon Rsg1 KD (Ctl [mean ± SD]: 1.78 ± 0.48 μm, n = 517 axonemes, 29 cells, 5 embryos vs. Rsg1 KD: 0.23 ± 0.34 μm, n = 361 axonemes, 28 cells, 5 embryos; ***P <0.0001). (d) Quantification of GFP-MAP7-positive compartments reveals a significant increase in proximal identity (Ctl: 1.90 ± 0.36 μm, n = 452 axonemes, 29 cells, 5 embryos vs. Rsg1 KD: 3.32 ± 0.95 μm, n = 364 axonemes, 39 cells, 5 embryos; ***P <0.0001). Scale bars represent 5 μm.