Expression In Limb Buds Research Articles

Chicken homeobox gene Msx-1: structure, expression in limb buds and effect of retinoic acid

A chicken gene carrying a homeobox highly homologous to the Drosophila muscle segment homeobox (msh) gene was isolated and designated as Msx-1. Conceptual translation from the longest ORF gave a protein of 259 amino acids lacking the conserved hexapeptide. Northern analysis detected a single 2.6 kb transcript. As early as day 2 of incubation, the transcript was detected but was not found in adult tissue. In situ hybridization analysis revealed that Msx-1 expression is closely related to a particular mesenchymal cell lineage during limb bud formation. In early stage embryos, Msx-1 was expressed in the somatopleure. When primordial mesenchyme cells for limb bud were generated from the Wolffian ridge of the somatopleure, Msx-1 expression began to diminish in the posterior half of the limb bud then in the presumptive cartilage-forming mesenchyme. In developing limb buds, remarkable expression was seen in the apical ectodermal ridge (AER), which is responsible for the sustained outgrowth and development of the limb. The Msx-1 transcripts were found in the limb mesenchymal cells in the region covering the necrotic zone and ectodermal cells overlying such mesenchymal cells. Both ectodermal and mesenchymal expression in limb bud were rapidly suppressed by local treatment of retinoic acid which can generate mirror-image duplication of digits. This indicates that retinoic acid alters the marginal presumptive non-cartilage forming mesenchyme cell lineage through suppression of Msx-1 expression.

Morphgenesis of chick limbs and retinoic acid.

Retinoic acid (RA) is a putative morphogen in the formation of chick limbs. We briefly reviewed recent advances in the study of mechanism for RA-induced duplication of the limbs. The discovery of RA receptor and its expression in limb buds may be promising breakthrough in the field. Furthermore, the correlated expressions of various types of the homeobox genes in limb buds may be a critical event in the limb morphogenesis.

Choline acetyltransferase in the chick limb bud.

In embryonic tissues a primitive cholinergic system is transiently expressed during morphogenesis. In the chick limb bud expression of the primitive cholinergic system in mesenchyme and central chondrogenic core precedes the appearance of the definitive cholinergic system in nerve and muscle. Here we show that, parallel to the expression of cholinesterase in mesenchyme and chondroblasts, embryonic cells are capable of acetylcholine synthesis. Choline acetyltransferase (ChAT) activity was measured by the radiometric assay of Fonnum (1975).