We have created a 2D morphometric analysis of the developing mouse hindlimb bud. This analysis has provided two useful resources for the study of limb development. First, a temporally accurate numerical description of shape changes during normal mouse limb development. Second, a web-based morphometric staging system, which has the advantage of being easy to use, and with a reproducibility of ab...

The prevailing view has long been that mesenchymal cells at the apex of the vertebrate limb bud proliferate in a progress zone (PZ) under the influence of the apical ectodermal ridge (AER). According to the PZ model, proximodistal cell fates are specified according to the time spent in the PZ. New results, considered along with some earlier findings, fail to support this model.

When it first appears at stage HH16, the wing bud is already polarized along the dorsoventral axis. To study the mechanisms leading to the establishment of its dorsoventral polarity, we decided to focus our attention on an earlier stage (HH13). Using the quail-chick chimera system, we first show that the presumptive wing mesoderm occupies the medial half of the somatopleure at the level of somi...

When polarizing mesoderm from the posterior border of the 4-day chick limb bud is placed adjacent to anterior limb mesoderm and ectodermal ridge, the anterior ridge thickens and mesodermal outgrowth ensues, resulting in supernumerary limb structures. This apposition of anterior and posterior limb tissues can be accomplished by cutting off the apical one third of the limb bud and reimplanting it...

Mutations in the murine limb deformity (ld) gene disrupt differentiation of the Apical Ectodermal Ridge (AER) and patterning of distal limb structures. However, initial outgrowth of the limb bud is not affected, suggesting that early and late functions of the AER are uncoupled. Similarly, activation of the 5' members of the HoxD gene cluster (Hoxd-11 to Hoxd-13) is not affected in ld mutant pos...

The chick limb bud is a powerful experimental system in which to study pattern formation in vertebrate embryos. Exogenously applied retinoic acid, a vitamin A derivative, can bring about changes in pattern and, on several grounds, is a good candidate for an endogenous morphogen. As such, the local concentration of retinoic acid might provide cells with information about their position in relati...

We summarize existing data and describe new information on the levels and distribution of cellular retinoic acid-binding protein (CRABP) and cellular retinol-binding protein (CRBP) in the regenerating axolotl limb, the developing chick limb bud and the nervous system of the chick embryo in the light of the known morphogenetic effects of retinoids on these systems. In the regenerating limb, leve...

The forelimbs of higher vertebrates are composed of two portions: the appendicular region (stylopod, zeugopod and autopod) and the less prominent proximal girdle elements (scapula and clavicle) that brace the limb to the main trunk axis. We show that the formation of the muscles of the proximal limb occurs through two distinct mechanisms. The more superficial girdle muscles (pectoral and latiss...

Vertebrate odd-skipped related genes (Osr) have an essential function during the formation of the intermediate mesoderm (IM) and the kidney structures derived from it. Here, we show that these genes are also crucial for limb bud formation in the adjacent lateral plate mesoderm (LPM). Reduction of zebrafish Osr function impairs fin development by the failure of tbx5a maintenance in the developin...

T H E limbs of amniote embryos are characterized by a thickening of the epiblast at their tips (Balfour, 1885). Kolliker (1879) illustrated such a thickening in a section of a chick embryo and, according to Braus (1906), was responsible for the term 'ectodermal cap' {Ektodermkappe). Saunders (1948) showed in the chick by experimental means that 'the thickened ectoderm at the apex of the bud' is...