Fig. S1. TEM sections through talpid³ neuroepithelium at stage HH24. Basal bodies (black arrow) with satellites (arrowhead), sister centrioles (s). No primary cilia project from cell surface into lumen, no ciliary vesicles are associated with basal bodies and in most cases basal bodies are not orientated toward apical membrane. Scale bars: 589nm.

Fig. S2. (A) Alignment of orthologous Talpid3 proteins from vertebrates and Nematostella vectensis. Multiple alignments made using MUSCLE and displayed with JalView. Predicted coiled-coil region from PCOILS analysis in Fig. S4 shown as a green box. A neighbouring region of high sequence homology purple box. The chicken sequence was used as the reference and so does not contain gaps. (B) Alignment of complete/partial Talpid3 proteins from vertebrates, and Strongylocentrolus purpuratus and Nematostella vectensis. Multiple alignments made using MUSCLE and displayed with JalView. All gaps in alignment retained.

Fig. S3. Sequence conservation of Talpid3 protein in vertebrates and Nematostella vectensis. Quality plot of sequence conservation produced by Plotcon, using a window of 33 residues and the BLOSUM62 sequence conservation scoring matrix. Predicted coiled-coil region from PCOILS analysis in Fig. S3 shown as green box. Neighbouring region of high sequence homology shown as purple box.

Fig. S4. Prediction of coiled-coil domain in Talpid3 protein. Weighted (a) and unweighted (b) predictions of coiled-coil regions were made using PCOILS and windows of 14 (green), 21 (blue) or 28 (red) residues. Helix wheels (c) were drawn using Pepwheels. Physical characteristics of residues are shown as hydrophobic (blue), positive charge (black) and negative charge (red).

Fig. S5. Predicted secondary structure of Talpid3 protein. Predictions of secondary structure made using SABLE and displayed with POLYVIEW. Alpha helix (red, H), β strand (green, E) and coil (blue, C) regions are displayed, with confidence scores (0-9). Physicochemical properties shown as hydrophobic (yellow), charges (orange) and polar (red). Predicted coiled-coil region from PCOILS analysis in Fig. S4 is shown as solid boxed region, neighbouring highly conserved region shown as a broken line.