Abstract:
The vertebrate body plan is characterized by a segmented organization, which is clearly visible at the level of the vertebral column, its associated muscles and the peripheral nervous system. This basic organization is first established during embryogenesis through the periodic formation of embryonic segments called somites. This process is associated with a
molecular oscillator - the segmentation clock - which was characterized in different vertebrate species on the basis of the periodic expression of so called cyclic genes in the tissue precursor of the somites, the presomitic mesoderm (PSM). So far, a handful of cyclic genes have been identified; most of them are linked to the Notch pathway. We have undertaken a
microarray approach to discover new cyclic genes, by analyzing time series of mouse PSM during one clock cycle. Due to
the limiting amount of starting RNA (50ng), our protocol includes two rounds of amplification, controlled for its reproducibility and quality. We performed a Fourier analysis to identify periodic expression profiles. As a validation of the method, known cyclic genes ranked among the most significant periodic genes detected. By hierarchically clustering the expression profiles, we identified a first cluster containing genes related to Notch and FGF signalings; the second one contained genes related to Wnt signaling. The most significant candidate cyclic genes were validated by in situ hybridization. Gene ontology analysis revealed a strong enrichment in signaling molecules. As a conclusion, the identification of these new cyclic genes link new temporally regulated signaling pathways to the clock regulation network.
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