Figure 5: Two rotating cilia are sufficient for L–R asymmetric gene expression in Dpcd and Rfx3 mutant embryos.

(a–u) The number of rotating cilia detected by a high-speed camera via transmitted light from a halogen lamp (a,d,g,j,m,p,s), flow velocity distribution (b,e,h,k,n,q,t), and L–R marker gene expression (c,f,i,l,o,r,u) were examined in individual Dpcd and Rfx3 mutant embryos at the four-to-six-somite stages. The embryo shown in (a–c) is the same embryo shown in Figure 4e. Coloured circles indicate rotating cilia, with red and pink circles denoting posteriorly tilted cilia; green and white circles denote rotating cilia showing no tilt. Expression of Cerl2 in the node and that of Pitx2 in the lateral plate mesoderm were examined as L–R markers. Asymmetric expression of Cerl2 and Pitx2 was maintained in the mildly affected mutant embryos (l,o,r,u). (v) Summary of the relation between the number of rotating cilia and Cerl2 expression. L–R asymmetric Cerl2 expression was impaired in embryos with no, or only one, rotating node cilium, whereas it was retained in those with two or more rotating cilia. (w) Flow velocity distribution for nodal flow in a wild-type (+/+) embryo at the four-somite stage. Global leftward flow is generated across the entire node cavity. The white and the black scale bars indicate 10 μm. The red and green scale bars indicate 70 μm and 0.5 mm, respectively. The black arrows indicate 5 μm s⁻¹.