1. Defining the node-streak border, caudal lateral epiblast and chordo-neural hinge.
Defining the node-streak border, caudal lateral epiblast and chordo-neural hinge. (A,B) Schematics of (A) mouse and (B) chick 2- to 6-somite (Aa,Ba) and 35- to 40-somite (Af,Bf) embryos, depicting the node and the tail bud regions (blue boxes) shown below. (Ab-Ad,Ag-Ai,Bb-Bd,Bg-Bi) Whole-mount in situ hybridisation of selected genes expressed in the node-streak border (NSB, red boxes in early embryos) and chordo-neural hinge (CNH, red boxes in late embryos): Bra (Ab,Ag,Bb,Bg); Foxa2 (Ac,Ah,Bc,Bh) and Fgf8 (Ad,Ai,Bd,Bi). Ab and Bb, ventral view; Ac,Ad,Ag-Ai,Bc,Bd,Bg-Bi, sagittal sections. Both Bra and Fgf8 are expressed in the NSB and the CNH in both species, but their expression extends further rostrally in the chick than in the mouse. Thus, in the chick, they cannot be considered markers of the NSB or CNH. Foxa2 labels the end of the neural tube and notochord in both species and can be used to localise the NSB and the CNH. (Ae,Aj,Be,Bj) Summary diagrams showing the similar topography of Foxa2 (dark red) and Fgf8 (orange) gene expression in the mouse and chick NSB and CNH. C, caudal; N, node; NC, notochord; NT, neural tube; PS, primitive streak; TBM, tail bud mesoderm; R, Rostral.
Valerie Wilson et al. Development 2009;136:
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