Fig. 1

Screening strategy to identify candidate head inhibitor genes in Hydra. a Anatomy of an intact Hydra. The apical extremity (head) is composed of a dome-shaped structure called hypostome, surrounded by a ring of tentacles. At the other extremity (foot), the basal disk allows the animals to attach. b The five criteria used to identify HI candidate genes. c, d Screening procedure applied to identify HI candidate genes: An RNA-seq dataset of 440 downregulated genes in β-catenin (RNAi) planarians was used to retrieve through blastx on NCBI (E value < 1e⁻¹⁰) 124 non-redundant Hydra sequences that correspond to 106 unique proteins (Supplementary Data 1). These candidates were next tested on RNA-seq data sets obtained in intact Hydra measured at five positions along the body axis (apical -Ap-, regions R1, R3, R4, basal -Ba-) to identify five apical-to-basal graded genes, which were tested on RNA-seq data sets obtained from regenerating tips taken at nine time points after a 50% or 80% bisection. Data available on HydrAtlas.unige.ch e Three genes downregulated after β-catenin(RNAi) in planarians, show an apical-to-basal graded expression in Hydra, and a minimal 1.5-fold upregulation in head-regenerating tips at 24 hpa. The 3rd column indicates the mean value of the number of reads measured in three biological replicates in the indicated regions. Fold Change (FC) measured in head-regenerating (HR) tips at 24 h post-amputation (hpa) over the values measured at time 0. f Wnt3 and HySp5 RNA-seq profiles in intact and regenerating animals. g HySp5 expression patterns in intact and regenerating Hydra tested as indicated after mid-gastric bisection in two independent experiments. Inset: magnified view of the apex. Scale bars: 250 μm