Figure 16.5. Specification of limb type by Tbx4 and Tbx5.

Figure 16.5

Specification of limb type by Tbx4 and Tbx5. (A) During normal chick development, in situ hybridizations show that Tbx5 is found in the anterior lateral plate mesoderm, while Tbx4 is found in the posterior lateral plate mesoderm. Tbx5-containing limb buds produce wings, while Tbx4-containing limb buds generate legs. (B) If a new limb bud is induced with an FGF-secreting bead, the type of limb formed depends upon the tbx gene expressed in the limb bud. If placed between the regions of Tbx4 and Tbx5 expression, the bead will induce the expression of Tbx4 posteriorly and Tbx5 anteriorly. The resulting limb bud will also express Tbx5 anteriorly and Tbx4 posteriorly and will generate a chimeric limb. (C) Expression of Tbx5 in the forelimb (w, wing) buds and in the anterior portion of a limb bud induced by an FGF-secreting bead. (The somite level can be determined by staining for Mrf4 mRNA, which is localized to the myotomes.) (D) Expression of Tbx4 in the hindlimb (le, leg) buds and in the posterior portion of an FGF-induced limb bud. (E, F) A chimeric limb induced by an FGF bead contains anterior wing structures and posterior leg structures. (A, B after Ohuchi et al. 1998, Ohuchi and Noji 1999; C-F photographs courtesy of S. Noji.)

From: Formation of the Limb Bud

Cover of Developmental Biology
Developmental Biology. 6th edition.
Gilbert SF.
Sunderland (MA): Sinauer Associates; 2000.
Copyright © 2000, Sinauer Associates.

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