Caudal Regulates the Spatiotemporal Dynamics of Pair-Rule Waves in Tribolium

In the short-germ beetle tribolium castaneum,waves of pair-rule gene expression propagate from the posterior end of the embryo towards the anterior and eventually freeze into stable stripes,partitioning the anterior-posterior axis into segments. similar waves in vertebrates are assumed to arise due to the modulation of a molecular clock by a posterior-to-anterior frequency gradient. however,neither a molecular candidate nor a functional role has been identified to date for such a frequency gradient,either in vertebrates or elsewhere. here we provide evidence that the posterior gradient of tc-caudal expression regulates the oscillation frequency of pair-rule gene expression in tribolium. we show this by analyzing the spatiotemporal dynamics of tc-even-skipped expression in strong and mild knockdown of tc-caudal,and by correlating the extension,level and slope of the tc-caudal expression gradient to the spatiotemporal dynamics of tc-even-skipped expression in wild type as well as in different rnai knockdowns of tc-caudal regulators. further,we show that besides its absolute importance for stripe generation in the static phase of the tribolium blastoderm,a frequency gradient might serve as a buffer against noise during axis elongation phase in tribolium as well as vertebrates. our results highlight the role of frequency gradients in pattern formation. © 2014 el-sherif et al.