Although mammals tend to be largely left/right symmetrical, there are differences between the two sides, particularly in the placement of internal organs. This ‘left-right symmetry breaking’ occurs very early in embryonic development. How do developing embryos differentiate in this way? Surprisingly, it is the movement of amniotic fluid across the developing embryo that creates the asymmetry.
Hiroshi Hamada and colleagues at Japan’s Osaka University have previously demonstrated that beating cilia on the early embryonic cells can cause the differential movement of amniotic fluid. The cilia are positioned so that they create a leftward flow of amniotic fluid.
New research by Hamada and his team has identified a set of genes in mice that are involved in directing the placement of the cilia. They looked at genes from the ‘Dishevelled’ family (don’t you love geneticists?) and found that mutations in these genes did in fact prevent the cilia from migrating to the proper position on the cell. Mouse embyros with these mutations did not display the normal left-right symmetry breaking.This finding could impact research on human birth defects.