Figure 1: Asymmetric Cerl2 expression is established when leftward flow is weak.
(a) Velocity distribution of nodal flow in mouse embryos at the EHF and two-somite (2-som) stages. (b) Cerl2 expression in the perinodal region (top panel) and leftward velocity of nodal flow (bottom panel) at various stages of development. The level of left-sided expression of Cerl2 relative to that on the right is indicated by=(equal to) or < (less than). In the present study, we define 'local leftward flow' as the flow field with a leftward flow speed, U, in the range of 1.0–2.0 μm s−1. Red closed circles, blue open circles, orange asterisks, and green triangles denote velocity of L, R, posterior, and anterior directional flows, respectively. Values represent the 90th percentile (top 10th percentile) of the velocity distribution ±5% error bars. Three embryos were examined for analysis of flow velocity. (c) Quantification of Cerl2 expression level in the node. Cerl2 expression in the node was examined at various stages by whole mount in situ hybridization. 1so, one somite stage; 2so, two-somite stage. The level of Cerl2 expression on both sides of the node was quantified by measuring the pixel intensity of signals obtained by whole mount in situ hybridization. Multiple embryos were examined for each stage; n=7 for EHF; n=12 for LHF; n=7 for one-somite; n=6 for two-somite. The L–R asymmetry in Cerl2 expression appears at the LHF stage (in ∼50% of the LHF embryos). The black scale bar indicates 10 μm. The black arrow indicates 5 μm s−1.
