Quantification of the posterior to anterior propagation of spaw, pitx2 and lft1. A: At 15 somite stage (SS), the anterior boundary of lateral plate mesoderm (LPM) spaw was at somite 7. Green arrowhead: anterior expression boundary of spaw. Red arrowhead: somite corresponding to the anterior expression boundary of spaw, pitx2 or lft1. B: At 15 SS, the anterior boundary of LPM pitx2 expression was at somite 10. C,D: lft1 expression in the midline was bi-phasic. C: In the first phase, static lft1 expression was present in posterior midline before the LPM spaw expression at 10 SS. D: At approximately 15 SS, the second propagation phase of lft1 expression started. Green arrow: spaw expression. Blue arrowhead: anterior expression boundary of lft1 expression. A,B: Anterior to the left. C,D: Anterior to the top. E: Quantitative analysis of posterior-to-anterior (PA) propagation of spaw (n = 213), pitx2 (n = 74) and lft1 (n = 124). X axis is the development stages defined by total number of somite pairs. Y axis is the position of anterior expression boundary of each gene. A negative number means the anterior expression domain is anterior to the somitogenesis region. Almost 100% of embryos had detectable expression of spaw and pitx2 at stage 13 SS, 14 SS, respectively. Error bars are ± standard error.
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