Fig. 5

Expression of Lim3 in the spinal cord of no tail (ntl) and floating head (flh) mutant zebrafish. Twenty-eight-hour embryos were dissected from the yolk and flatted under a coverslip (A–D), or sectioned (E,F). Anterior is to the left, except in E. (A) Ventral view of the anterior spinal cord in a ntl mutant. There is clear separation of Lim3-positive cells across the midline. The first somite is marked with an asterisk and somite borders are indicated by hash marks. (B) Lateral view of ntl embryo at the level of the trunk. The Lim3-positive cells are restricted to the ventral spinal cord, but with a slightly broader distribution than in the wild type and an apparent loss of segmental organization. (C) Ventral view of an flh-mutant anterior spinal cord. The first somite is marked by an asterisk. An excess number and loss of organization of Lim3-positive cells is observed in the anterior spinal cord of the mutant embryos. Variably, around the level of the fifth somite, the midline separation of Lim3-positive cells breaks down (arrows). (D) Lateral view of flh embryo at the posterior end of the trunk. At this level, areas with unorganized clumps of Lim3-positive cells alternate with areas lacking Lim3-positive; in the tail of flh mutants there is no Lim3 expression. (E) Cross section of flh-mutant anterior spinal cord, double labeled with anti-Lim3 antibody (purple) and monoclonal antibody MZ15 which stains notochord and floor plate (brown). MZ15 staining is seen only on the ventricular surface of the spinal cord, and Lim3-positive cells are present across the midline. In flh mutants, axial mesodermal cells are transfated from notochord to somitic mesoderm (S). (F) Parasagital section of the posterior trunk region of a Lim3 (purple) and MZ15 (brown) double-labeled flh mutant embryo. Lim3 expression correlates with expression of MZ15. Scale bar is 50 μm in A–D and F, and 70 μm in E.