Differential cell adhesive properties are known to regulate important developmental events like cell sorting and cell migration. Cadherins and protocadherins are known to mediate these cellular properties. Though a large number of such molecules have been predicted, their characterization in terms of interactive properties and cellular roles is far from being comprehensive. To narrow down the tissue context and collect correlative evidence for tissue specific roles of these molecules, we have carried out whole-mount in situ hybridization based RNA expression study for seven cadherins and four protocadherins. In developing chicken embryos (HH stages 18, 22, 26 and 28) cadherins and protocadherins are expressed in tissue restricted manner. This expression study elucidates precise expression domains of cell adhesion molecules in the context of developing embryos. These expression domains provide spatio-temporal context in which the function of these genes can be further explored.

Differentiated tissues may be considered as materials with distinct properties. The differentiation program of a given tissue ensures that it acquires material properties commensurate with its function. It may be hypothesized that some of these properties are acquired through production of tissue-specific metabolites synthesized by metabolic enzymes. To establish correlation between metabolism and organogenesis we have carried out a genome-wide expression study of metabolism related genes by RNA in-situ hybridization. 23% of the metabolism related genes studied are expressed in a tissue-restricted but not tissue-exclusive manner. We have conducted the screen on whole mount chicken (Gallus gallus) embryos from four distinct developmental stages to correlate dynamic changes in expression patterns of metabolic enzymes with spatio-temporally unique developmental events. Our data strongly suggests that unique combinations of metabolism related genes, and not specific metabolic pathways, are upregulated during differentiation. Further, expression of metabolism related genes in well established signaling centers that regulate different aspects of morphogenesis indicates developmental roles of some of the metabolism related genes. The database of tissue-restricted expression patterns of metabolism related genes, generated in this study, should serve as a resource for systematic identification of these genes with tissue-specific functions during development. Finally, comprehensive understanding of differentiation is not possible unless the downstream genes of a differentiation cascade are identified. We propose, metabolic enzymes constitute a significant portion of these downstream target genes. Thus our study should help elucidate different aspects of tissue differentiation.

Des programmes de cartographie des génomes des principales espèces animales d’intérêt économique se sont développés depuis quelques années. Cet article fait le point sur l’état d’avancement et les perspectives d’utilisation de la carte génétique porcine. Après une présentation des principes généraux de la cartographie génétique, les résultats des principaux programmes de cartographie du génome porcin sont présentés. Différentes perspectives d’utilisation des cartes génétiques sont ensuite évoquées. Les possibilités et les modalités d’utilisation des marqueurs génétiques pour la détection et la localisation de locus à effets quantitatifs (QTL) sont présentées. L’intérêt de la cartographie comparée pour l’identification des QTL est illustré à partir de l’exemple du système majeur d’histocompatibilité. Quelques perspectives d’utilisation de l’information apportée par les marqueurs dans les programmes d’amélioration génétique (introgression d’un gène, sélection assistée par marqueurs) sont ensuite évoquées. Enfin, les principaux programmes de recherche utilisant la carte génétique porcine actuellement en cours à l’INRA (programmes de localisation de gènes RN et MU, programme de recherche des QTL responsables de la variabilité génétique entre les races Meishan et Large White) sont présentés.