Fig. 9.

Effects of retinoic acid (RA) signaling alterations on development of hu/elav-expressing cells in amphioxus. a–e′ Larvae at 30 hpf (hours post fertilization) and f–j′ larvae at 36 hpf are shown in lateral view (a–j) and dorsal view (a′–j′). a, a′, f, f′ Control animals treated with DMSO at 6 hpf. Dotted lines indicate the mid-trunk area, where a particularly high density of ectodermal sensory neuron progenitors (ESNPs) is observed (compare with Additional file 7: Figure S4). b, b′, d, d′, g, g′, i, i′ Animals treated with the RA receptor (RAR) antagonist BMS493 at two different developmental stages, 6 or 24 hpf. c, c′, e, e′, h, h′, j, j′ Animals treated with all-trans RA at two different developmental stages, 6 or 24 hpf. The treatment time point (t), 6 or 24 hpf, is indicated in the upper right corner of each image set. Scale bars are 50 µm. The scale bar in a also applies to a′, b–e′, and the scale bar in f also applies to f′, g–j′