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Fig. 1. Schematized morphogenesis of vertebrate and arthropod neurectoderm.
Vertebrate and arthropod ectoderm viewed in cross-section (grey circles
represent non-neural ectoderm). Vertebrate neurectoderm (colored boxes) is
positioned dorsally (top of figure) on the body. Later neurectoderm undergoes
morphogenesis (direction indicated by arrowhead) to form a neural tube,
internal to the non-neural ectoderm. Dorsal CNS (D; red) is initially lateral,
intermediate CNS (I; green) is initially intermediate and ventral CNS (V;
blue) is initially medial. Arthropod neurectoderm (colored boxes) is
positioned ventrally (bottom of figure) on the body. The nerve cord forms as
neuroblasts bud off toward the interior of the embryo (direction of
arrowhead). Later in development, the arthropod nerve cord contains layers of
neurons. Early, members of the vnd/Nkx gene family are expressed in the
ventral domain (blue) and members of the msh/Msx gene family are expressed in
the dorsal (red) domain of both vertebrates and flies (see text for details).
In flies, ind is expressed early in the intermediate domain. Although
vertebrate ind homologs (Gsh) are expressed in a subset of
intermediate domain cells, they are expressed early only in anterior CNS and
much later in spinal cord (Deschet et al.,
1998; Cheesman and Eisen,
2004; Valerius et al.,
1995).
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