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Presents a study that described the development of a system in which mouse embryos are cultured under an artificial fluid flow. Relation between the direction of the intrinsic nodal flow and that of the pump-driven artificial flow; Reversal of the intrinsic nodal flow by fast rightward artificial flow; Reversal of situs of wild-type embryos at the presomite stage by fast rightward flow.

Abstract: Left–right (L–R) asymmetry in the mouse embryo is generated in the node and is dependent on cilia-driven fluid flow, but how the initial asymmetry is transmitted from the node to the lateral plate has remained unknown. We have now identified a transcriptional enhancer (ANE) in the human LEFTY1 gene that exhibits marked L>R asymmetric activity in perinodal cells of the mouse embryo. Dissection of ANE revealed that it is activated in the perinodal cells on the left side by Nodal signaling, suggesting that Nodal activity in the node is asymmetric at a time when Nodal expression is symmetric. Phosphorylated Smad2/3 (pSmad2) indeed manifested an L–R asymmetric distribution at the node, being detected in perinodal cells preferentially on the left side. This asymmetry in pSmad2 distribution was found to be generated not by unidirectional transport of Nodal but rather as a result of LR distribution of active Nodal in the node is translated into the asymmetry in LPM. [Copyright &y& Elsevier]