The recombinant limb as a model for the study of limb patterning, and its application to muscle development

Abstract

The recombinant limb is a model system that has proved fruitful for analyzing epithelial-mesenchymal interactions and understanding the functional properties of the components of the limb bud. Here we present an overview of some of the insights obtained through the use of this technique. Among these are the understanding that fore or hind limb identity is inherent to the limb bud mesoderm, that the apical ectodermal ridge (AER) is a permissive signaling center and that the limb bud ectoderm plays a central role in the control of dorsoventral polarity. Recombinant limb studies have also allowed the identification of the affected tissue component in several limb mutants. More recently this model has been applied to the study of regulation of gene expressions related to patterning. In this report we use recombinant limbs to analyze pattering of the Pax3 expressing limb muscle cell lineage in the early stages of limb development. In recombinant limbs made without the zone of polarizing activity (ZPA), myoblasts appear intermingled with other mesodermal cells at the beginning of the recombinant limb development. Rapidly thereafter, the muscle precursors segregate and organize around the central forming chondrogenic core of the recombinant. Although this segregation is reminiscent of that occurring during normal development, the myoblasts in the recombinant fail to proliferate appropriately and also fail to migrate distally. Consequently, the muscle pattern in the recombinant limb is defective indicating that normal patterning cues are absent. However, recombinant limbs polarized with a ZPA exhibited a larger mass of muscle cells and a more normal morphogenesis, supporting a role for this signaling center in limb muscle development. Finally, we have ruled out host somite contributions to recombinant limbs by grafting chick recombinant limbs to quail hosts. This initial report demonstrates the value of the recombinant limb model system for dissecting the environmental cues required for normal muscle limb patterning.

Specific mesenchymal/epithelial induction of olfactory receptor, vomeronasal, and gonadotropin‐releasing hormone (GnRH) neurons

“…Indeed, the degree of ORN differentiation seen in frontonasal M/E explants is far greater than that reported for odontogenic cells in branchial arches, or cartilage, muscle and bone in limb buds in vitro (reviewed by Fernandez-Teran et al, 1999; Hay, 2005; Modino & Sharpe, 2005). By varying M/E interactions specifically and reproducibly alter signaling and transcriptional regulation, we elicit tissue specific (i.e.…”

“…Removal or relocation of tissues has been an essential experimental approach for understanding specificity of induction and differentiation in accessible embryos for nearly a century (reviewed by Saunders et al, 1976; Hamburger, 1988; LeDourain et al, 1997; Fernandez-Teran et al, 1999; Landmesser, 2001); however, even the most sophisticated intrauterine imaging and manipulation (e.g. Gaiano et al, 1999) is not likely to facilitate consistent, successful extirpation or translocation of frontonasal tissue, which give rise to the OE, in intact mammalian embryos.…”

Initiation of Proximal-Distal Patterning in the Vertebrate Limb by Signals and Growth

“…After several days of development in the host egg, recombinant limbs are patterned by endogenous signals and form recognizable skeletal structures (14, 15). …”

The chickoligozeugodactyly(ozd) mutant lacks sonic hedgehog function in the limb

“…To investigate which tissue layer is affected by the ozd mutation we performed recombination experiments interchanging mesoderm and ectoderm between mutant and normal donors (Fernandez-Teran et al, 1999). Control experiments exchanging mesoderm and ectoderm from normal limb buds resulted in completely normal skeletal patterns (Fig.…”