Andrew Lumsden and Susanne Dietrich 1 Introduction

Many patterning structures have been identified by microsurgical manipulation of chick embryos in ovo, such as ablation or heterotopic grafting experiments. Among the structures studied, the notochord has received much attention, since it plays a crucial role in the development of the surrounding tissues. In the overlying neural tube (Fig. 1), the notochord induces the ventral midline structure, the floor plate, which subsequently specifies neuronal cell types in the ventral half of the neural tube (reviewed in ref. 2). In the paraxial mesoderm that flanks the neural tube and notochord, the latter induces the scle-rotome and, in synergy with signals from dorsal neural tube or surface ectoderm, the epaxial myotome (3, reviewed in ref. 4). Studies on zebrafish notochord mutants suggest that the notochord also acts in the formation of the dorsal aorta (5). Finally, the proximity of notochord and the subjacent endo-derm during early phases of development suggests that the notochord may play a role in the development of the roof of the gut.

Much of the function of the notochord in these tissue interactions has been attributed to the signaling molecule sonic hedgehog (Shh; reviewed in 2,6,7). However, in mice lacking Shh, notochord-dependent structures develop to some extent (8). Thus, the notochord will remain the subject of many embryological studies in the future. Therefore, we will describe notochord heterotopic transplantation in chick embryos as one approach to study the functions of this structure in vivo. It should be noted, however, that many other tissues in the chick embryo can be grafted using similar methods. Similarly, corresponding structures from quail embryos may be grafted into chick hosts, allowing the detection of quail cells with quail-specific markers (9). Finally, tissues derived from mouse embryos have successfully been transplanted to chick hosts using this approach (10).

From: Methods in Molecular Biology, Vol. 97: Molecular Embryology: Methods and Protocols Edited by: P. T. Sharpe and I. Mason © Humana Press Inc., Totowa, NJ

Fig. 1. Repatterning of the neural tube after ectopic notochord insertion (1). (A,B) sections of embryos hybridized with the dorsal neural tube marker Pax3. (C,D) Sections of embryos hybridized with the intermediate marker Pax6. A, C, controls, B, D, sections of operated embryos. Where the ectopic notochord (N') has established contact to the neural tube, it induces a wedge-shaped structure normally found ventrally in the neural tube: the floor plate. Simultaneously, the graft suppresses the expression of the dorsal marker Pax3 and the intermediate marker Pax6.

Fig. 1. Repatterning of the neural tube after ectopic notochord insertion (1). (A,B) sections of embryos hybridized with the dorsal neural tube marker Pax3. (C,D) Sections of embryos hybridized with the intermediate marker Pax6. A, C, controls, B, D, sections of operated embryos. Where the ectopic notochord (N') has established contact to the neural tube, it induces a wedge-shaped structure normally found ventrally in the neural tube: the floor plate. Simultaneously, the graft suppresses the expression of the dorsal marker Pax3 and the intermediate marker Pax6.

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