Fig. 3. Expression of HyBra1 and HyBra2. HyBra1 and HyBra2 mRNA expression was assessed in adult polyps (A-D) and during budding (E-J). (A,B) In adult hydras HyBra1 is predominantly expressed in the endodermal layer of the hypostome. (C,D) HyBra2 expression was primarily detected in the ectoderm of the hypostome. (B,D) Vibratome cross-sections of the hypostome. (E-J) Both genes are expressed very early during budding, but HyBra1 RNA is predominantly in the endoderm, whereas HyBra2 expression is restricted to the ectoderm (arrows in E and H). (J) Vibratome section of stage 5 bud. (K-M) Switch of HyBra2 expression from the endoderm to the ectoderm during head regeneration. Expression is in the endoderm at 18 hours (K), in both layers at 28 hours (L) and in the ectoderm by 48 hours (M). Arrows indicate the mesoglea, which separates ectoderm from endoderm.