Interaction between Notch and BMP receptor signaling in the cerebellar primordium. (a-f) Stage 10 to 12 chick embryos were electroporated in ovo with a GFP reporter plasmid and the expression plasmids described below. After two days of incubation, embryos were processed for cryosectioning, and the sections processed by in situ hybridization for Cath1. Adjacent sections were photographed for GFP and Cath1 in each experiment. (a, b) GFP alone. (c, d) GFP and caBMPR1b. (e, f) GFP, Notch1 ICD, and caBMPR1b. In the case of caBMPR1b and Notch1 ICD/caBMPR1b electroporations, additional sections were stained by immunohistochemistry for GFP (green) and phosphorylated (g, i, j) Smad1 and (h, k, l) Msx1/2 expression (red; green and red channels are shown separately to the left of each overlay). The rostral cerebellar primordium is outlined with a dashed oval. In the caBMPR and Notch1 ICD/caBMPR Msx1/2 stainings shown in (k, l), GFP/Msx1/2+ and GFP/Msx1/2- cells were counted across sections from three electroporated cerebella each and represented as columns. Scale bar in (f) represents 100 μm.