Fig. 1

Lbx-A gene in expression in lamprey and hagfish embryos. a A pre-ammocoete larva doubly stained with phalloidin (green; skeletal muscles) and acetylated tubulin antibody (green; neurons). HBM, hypobranchial muscle; m, mouth; XII, hypoglossal nerve. b–e Expression of LjLbx-A gene in the rostral part of lamprey embryos. Arrowheads indicate the rostral end of hypobranchial muscle (HBM) primordia. Arrows indicate the ventral edge of the extending body wall muscle primordia. b, d Left lateral views. c Ventral view. e Left-ventral view. f Differentiated somitic muscles visualized by myosin heavy chain antibody MF20. g–l Anterior portion of the stage 30 embryos stained with MyHC antibody MF20, viewed from the left (g, i, k) and right (h, j, l) sides. Compared to the embryos injected with Cas9 only (g, h), LjLbx-A-disrupted embryos have thinner and shorter HBM (i–l). m 3D reconstruction of an HE-stained stage 53 hagfish embryo showing location of the hypobranchial-equivalent muscle anlage (dark green; Oisi et al. [17]). Dorsolateral segmented muscles (m. par) are shown by the repeated pattern of light greens. m. obl/rect, anterior oblique muscles and the rectus muscles; m. par, parietal muscles. n, o Expression of EbLbx-A in the trunk of stage 53 hagfish embryo. Arrowheads show the expression at the ventral edge of the somites. Transverse sections at pharyngeal (n) and cloacal (o) levels. no, notochord; nt, neural tube. Scale bars, 200 mm