Cell Movements at Hensen’s Node Establish Left/Right Asymmetric Gene Expression in the Chick

TLDR: It is shown that asymmetric cell rearrangements take place within chick embryos, creating a leftward movement of cells around the node, which represents an alternative strategy for breaking L/R symmetry in gene activity.

Abstract: In vertebrates, the readily apparent left/right (L/R) anatomical asymmetries of the internal organs can be traced to molecular events initiated at or near the time of gastrulation However, the earliest steps of this process do not seem to be universally conserved In particular, how this axis is first defined in chicks has remained problematic Here we show that asymmetric cell rearrangements take place within chick embryos, creating a leftward movement of cells around the node It is the relative displacement of cells expressing sonic hedgehog (Shh) and fibroblast growth factor 8 (Fgf8) that is responsible for establishing their asymmetric expression patterns The creation of asymmetric expression domains as a passive effect of cell movements represents an alternative strategy for breaking L/R symmetry in gene activity