Segmentation Clock

In most animal species, the anteroposterior body axis is generated by the formation of repeated structures called segments. In vertebrate segmentation, a specialized mesodermal structure called the somite gives rise to sceletal muscles, vertebrae, and some dermis. Formation of the somites is a rhythmic process that involves an oscillator - the segmentation clock - driven by Wnt and Notch signaling. The clock ticks in somite precursors and halts when they reach a specific maturation stage defined as the wavefront, established by FGF and Wnt signaling.. Here we present the expression sequence of Lunatic fringe and axin mRNAs during the formation of the two somites. The Lunatic fringe was shown to act downstream of Notch and to bind and negatively regulate its own promoter. Another cyclic gene is hes1. It acts also downstream of Notch and codes for an unstable protein able to negatively regulate its own promoter too.

Contributor: Kosi Gramatikoff, PhD

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