The polarizing region is a major signalling tissue involved in patterning the tissues of the vertebrate limb. The polarizing region is located at the posterior margin of the limb bud and can be recognized by its ability to induce additional digits when grafted to the anterior margin of a chick limb bud. The signal from the polarizing region operates at the tip of the bud in the progress zone, a...

The purpose of this experiment was to examine the relationship, if any, between nerve fibers and the formation of muscle pattern in the regenerating amphibian limb. During embryogenesis, nerve fibers grow into the limb bud at the time when the common muscle blastemas subdivide into individual muscle primordia, whereas in regeneration nerve fibers are always present. In order to learn whether or...

Myogenic Regulatory Factors (MRFs) are a family of transcription factors whose expression in a cell reflects the commitment of this cell to a myogenic fate before any cytological sign of muscle differentiation is detectable. Myogenic cells in limb skeletal muscles originate from the lateral half of the somites. Cells that migrate away from the lateral part of the somites to the limb bud do not ...

Both Hensen's node, the organizer center in chick embryo, and exogenous retinoic acid are known to induce limb duplication when grafted or applied to the host chick limb bud. Retinoic acid is known to be present in the node and has been proposed as the putative morphogen for chick limb development. Here, we report that Hensen's node from vitamin A-deficient quail embryo induces limb duplication...

In this paper, we review the major mathematical and computational models of vertebrate limb development and their roles in accounting for different aspects of this process. The main aspects of limb development that have been modeled include outgrowth and shaping of the limb bud, establishment of molecular gradients within the bud, and formation of the skeleton. These processes occur interdepend...

The purpose of this experiment was to examine the relationship, if any, between nerve fibers and the formation of muscle pattern in the regenerating amphibian limb. During embryogenesis, nerve fibers grow into the limb bud at the time when the common muscle blastemas subdivide into individual muscle primordia, whereas in regeneration nerve fibers are always present. In order to learn whether or...

Preaxial polydactyly (PPD) is a common limb-associated birth defect characterized by extra digit(s) in the anterior autopod. It often results from ectopic sonic hedgehog (Shh) expression in the anterior limb bud. Although several transcription factors are known to restrict Shh expression to the posterior limb bud, how they function together remains unclear. Here we provide evidence from mouse c...

Stage-dependent cell sorting in vitro is an intriguing property that mesenchymal cells of a chick limb bud have. We previously proposed that N-cadherin, a cell adhesion molecule, is involved in the sorting process and is likely to be a component of the mechanism of proximal-distal patterning in the developing limb (Yajima et al., (1999) Dev. Dynam. 216:274-284). Here, we present more direct evi...

We have recently shown in mice that four members of the T-box family of transcription factors (Tbx2-Tbx5) are expressed in developing limb buds, and that expression of two of these genes, Tbx4 and Tbx5, is primarily restricted to the developing hindlimbs and forelimbs, respectively. In this report, we investigate the role of these genes in limb specification and development, using the chick as ...

The positional signal localized to the posterior (zone of polarizing activity or ZPA) region of the vertebrate limb is transiently expressed during development and a decline in ZPA signaling is accelerated when posterior cells are dissociated and cultured in vitro. The evidence that cultured posterior cells display a precocious decline in ZPA signaling when compared to in vivo studies suggests ...