Abstract
Somitogenesis, the segmentation of the antero-posterior axis in vertebrates, is thought to result from the interactions between a genetic oscillator and a posterior-moving determination wavefront. The segment (somite) size is set by the product of the oscillator period and the velocity of the determination wavefront. Surprisingly, while the segmentation period can vary by a factor three between 20 °C and 32 °C, the somite size is constant. How this temperature independence is achieved is a mystery that we address in this study. Using RT-qPCR we show that the endogenous fgf8 mRNA concentration decreases during somitogenesis and correlates with the exponent of the shrinking pre-somitic mesoderm (PSM) size. As the temperature decreases, the dynamics of fgf8 and many other gene transcripts, as well as the segmentation frequency and the PSM shortening and tail growth rates slows down as T–Tc (with Tc = 14.4 °C). This behavior characteristic of a system near a critical point may account for the temperature independence of somitogenesis in zebrafish.
Highlights
Somitogenesis, the segmentation of the antero-posterior axis in vertebrates, is thought to result from the interactions between a genetic oscillator and a posterior-moving determination wavefront
As the temperature T is lowered we find that the dynamics of fgf[8] and many other genes implicated in somitogenesis and cellular differentiation slow down by the same factor, namely as (T−Tc)
We monitored the dynamics of Erk during somitogenesis in transgenic zebrafish (DREKA) embryos expressing a fluorescent reporter which cytoplasmic localization increases upon increasing Erk phosphorylation[14,15]
Summary
Somitogenesis, the segmentation of the antero-posterior axis in vertebrates, is thought to result from the interactions between a genetic oscillator and a posterior-moving determination wavefront. Accomplished by a stripe of gene expression that is thought to result from the interactions between a genetic oscillator and a posterior-moving determination wavefront This pre-pattern determines the position of the somite. 1976, is currently used to describe the output of the complex genetic network underlying the formation of this pre-pattern In this framework, periodic oscillations (the segmentation clock) that move anteriorly (in the PSM reference frame4), pass through a determination wavefront moving posteriorly (in both the lab and the PSM reference frames) and stop oscillating. A stripe of genes such as mesp[2] are activated to establish the future boundary of the following somite[1] In this model, the size of a somite is determined by the distance traveled by the determination wavefront during one cycle of the segmentation clock[4,5]. The segmentation clock driving the differentiation of the PSM into somites at the determination wavefront, has been amply studied and described[4,6] and is not the subject of this work
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