Neural tube slice preparation for live imaging. (A) Unturned embryo E8.5 with first appearance of somite pairs. (B) Neural tube dissected in pre-warmed medium using a micro-knife. (C) Slice of the neural tube mounted ventral side down on the poly-L-lysine coated glass bottom dish. (D) Small amount of a mixture made from petroleum jelly and wax applied around the neural tube and gently covered by a narrow piece of glass coverslip. Bar is 300 μm (B).