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First published online 25 June 2008
doi: 10.1242/dev.019877

Development 135, 2555-2562 (2008)
Published by The Company of Biologists 2008
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Mesp2 and Tbx6 cooperatively create periodic patterns coupled with the clock machinery during mouse somitogenesis

Masayuki Oginuma1, Yasutaka Niwa2, Deborah L. Chapman3 and Yumiko Saga1,4,*

1 Department of Genetics, SOKENDAI, 1111 Yata, Mishima, Shizuoka 411-8540, Japan.
2 Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan.
3 Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, PA 15260, USA.
4 Division of Mammalian Development, National Institute of Genetics, Yata 1111, Mishima 411-8540, Japan.

* Author for correspondence (e-mail: ysaga{at}lab.nig.ac.jp)

Accepted 27 May 2008

The metameric structures in vertebrates are based on the periodicity of the somites that are formed one by one from the anterior end of the presomitic mesoderm (PSM). The timing and spacing of somitogenesis are regulated by the segmentation clock, which is characterized by the oscillation of several signaling pathways in mice. The temporal information needs to be translated into a spatial pattern in the so-called determination front, at which cells become responsive to the clock signal. The transcription factor Mesp2 plays a crucial role in this process, regulating segmental border formation and rostro-caudal patterning. However, the mechanisms regulating the spatially restricted and periodic expression of Mesp2 have remained elusive. Using high-resolution fluorescent in situ hybridization in conjunction with immunohistochemical analyses, we have found a clear link between Mesp2 transcription and the periodic waves of Notch activity. We also find that Mesp2 transcription is spatially defined by Tbx6: Mesp2 transcription and Tbx6 protein initially share an identical anterior border in the PSM, but once translated, Mesp2 protein leads to the suppression of Tbx6 protein expression post-translationally via rapid degradation mediated by the ubiquitin-proteasome pathway. This reciprocal regulation is the spatial mechanism that successively defines the position of the next anterior border of Mesp2. We further show that FGF signaling provides a spatial cue to position the expression domain of Mesp2. Taken together, we conclude that Mesp2 is the final output signal by which the temporal information from the segmentation clock is translated into segmental patterning during mouse somitogenesis.

Key words: Notch signaling, Tbx6, Segmentation clock, Presomitic mesoderm, Mouse






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