2 MOLECULAR-MODELS OF INITIAL LEFT-RIGHT ASYMMETRY GENERATION

Left-right (LR) asymmetry is a fascinating problem in embryonic morpho genesis. Recently, a pathway of genes has been identified which is inv olved in LR patterning in vertebrates. Although this work characterize s the interactions of several asymmetrically-expressed genes, it is st ill entirely unclear how such asymmetric expression is set up in the f irst place. There are two promising molecular candidates which may pla y a role is such a process: the motor protein dynein, and the gap junc tion protein connexin-43 (Cx43). We present two models, significantly supported by previous findings, which hypothesize that (a) dynein asym metrically localizes LR determinants in individual cells to establish cell-autonomous LR biasing, and (b) asymmetric activity of Cx43 gap ju nctions within key cells sets up electric potentials in multicellular fields, thus establishing large-scale LR asymmetry.