Fig. 2. The less Hh signal, the fewer primary motoneurons, but all embryos still form median floor plate. Lateral views of islet2 expression in blue (A,B,D,E) and 
-collagen type II expression in red (A,B) at 18-21 h (18-22 somites) in wild-type uninjected embryo (A); MO-injected syu mutant (B); and embryos from a triple mutant cross (D,E). (B) entirely lacked primary motoneurons but still formed median floor plate. (D) has no islet2-expressing primary motoneurons and is presumably a cyc-/-;flh-/-;syu-/- triple mutant. (E) has only six islet2-expressing primary motoneurons but has a notochord (*) and is probably cyc-/-;flh+/-;syu-/- or cyc-/-;flh+/+;syu-/-. (C) shows total number of embryos from all the morpholino injection experiments that formed six or fewer islet2-expressing primary motoneurons. These are broken down into embryos from syu+/- parents (blue) or syu+/-;smu+/- parents (pink) injected with twhh-MO + ehh-MO and the one syu mutant injected with twhh-MO that formed six primary motoneurons (green). (F) The number of motoneurons in individual triple mutants. These were embryos from cyc+/-;flh+/-;syu+/- parents that had no notochord and five or fewer primary motoneurons. islet2 experiment, n=609: expect about 9.5 triple mutants; observed eight embryos with five or fewer motoneurons. islet1 experiment, n=549: expect about 8.5 triple mutants; observed seven embryos with five or fewer motoneurons. islet1 + islet2 experiment, n=367: expect about 5.7 triple mutants; observed four embryos with four or fewer motoneurons. Scale bar: 100 µm (A,B) and 250 µm (D,E).
