Issues and Specific Experimental Preparations

We will describe in detail several methods of analyzing some current and difficult problems in neural induction, including the relative roles of planar and vertical signaling in neural induction and patterning. However, many of

Fig. 5. Diagrams illustrate the concepts of vertical induction (A) and planar induction (B). In vertical induction, the organizer mesoderm (stippled) first involutes beneath the prospective neural tissue, and then sends signals radially (outward or vertically) to the overlying neural tissue (arrows, A). In planar induction, the Organizer mesoderm sends signals animally, from its posterior edge, into the prospective neural tissue (arrow, B). One difference is that vertical signaling requires involution of the Organizer and thus must occur at a relatively older stage (stage 10.5 shown in A), whereas planar signaling can occur early (stage 10- shown in B). The prospective fore- and midbrain (F, M), rhombencephalon (RH), and spinal cord (SC) are shown. The components of the organizer in the sagittal plane, the prospective prechordal mesoderm (PM) and notochordal mesoderm, are indicated with fine and course stippling, respectively.

Fig. 5. Diagrams illustrate the concepts of vertical induction (A) and planar induction (B). In vertical induction, the organizer mesoderm (stippled) first involutes beneath the prospective neural tissue, and then sends signals radially (outward or vertically) to the overlying neural tissue (arrows, A). In planar induction, the Organizer mesoderm sends signals animally, from its posterior edge, into the prospective neural tissue (arrow, B). One difference is that vertical signaling requires involution of the Organizer and thus must occur at a relatively older stage (stage 10.5 shown in A), whereas planar signaling can occur early (stage 10- shown in B). The prospective fore- and midbrain (F, M), rhombencephalon (RH), and spinal cord (SC) are shown. The components of the organizer in the sagittal plane, the prospective prechordal mesoderm (PM) and notochordal mesoderm, are indicated with fine and course stippling, respectively.

the issues, problems, and solutions described below are generic ones, applicable to other experiments as well.

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