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Fig. 4
Dorsal view (anterior to the left) of the expression pattern of the floor plate marker shh at the 15-somite stage in (A) wild-type, (B) flhtk241, (C) momth211, (D) ntltc41, (E) ntlts260 and (F) doctt258 embryos. (A) At the 15-somite stage shh is expressed in the notochord (weak, out of focus) and in the midline floor plate cell of the spinal cord (strong). (C) In momth211 embryos shh is expressed in a few faintly labeled cells in the ventral spinal cord. These cells frequently overlie cells in the dorsal mesoderm expressing both shh and ntl (arrowheads, out of focus). (D) Note that in embryos with the strong allele, ntltc41, no expression of shh in the axial mesoderm is detectable. (E) Axial mesodermal expression of shh is strongly reduced in mutant embryos with the weak allele, ntlts260.