Cilia propel the embryo in the right direction

Cilia have long been suspected to play a role in the determination of left- right asymmetry. Humans with the dominantly inherited condition Kartagener syndrome have defective cilia and a 50% incidence of mirror-image positioni ng of their organs (situs inversus). Analysis of mouse mutations affecting ciliary biogenesis and motility has demonstrated that the molecular motors kinesin and dynein are required to establish normal handed organismal asymm etry. The cilia that propel formation of the embryonic left-right axis are not conventional cilia, but monocilia. They are found on the node, or organ izer, of the gastrulation-stage mouse embryo where they drive net leftward movement of the fluid surrounding the node, and initiate left-right asymmet ry. (C) 2001 Wiley-Liss, Inc.