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First published online August 4, 2003
doi: 10.1242/10.1242/dev.00627

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Anterior and posterior waves of cyclic her1 gene expression are differentially regulated in the presomitic mesoderm of zebrafish

Martin Gajewski^1,*, Dirk Sieger^1,*, Burkhard Alt¹, Christian Leve¹, Stefan Hans², Christian Wolff³, Klaus B. Rohr² and Diethard Tautz^1,

¹ Universität zu Köln, Institut für Genetik, Weyertal 121, 50931 Köln, Germany
² Universität zu Köln, Institut für Entwicklungsbiologie, Gyrhofstr. 17, 50923 Köln, Germany
³ Max-Planck Institut für Entwicklungsbiologie, Spemannstrasse 35, 72076 Tübingen, Germany

Author for correspondence (e-mail: tautz{at}uni-koeln.de)

Accepted 27 May 2003

Somite formation in vertebrates depends on a molecular oscillator in the presomitic mesoderm (PSM). In order to get a better insight into how oscillatory expression is achieved in the zebrafish Danio rerio, we have analysed the regulation of her1 and her7, two bHLH genes that are co-expressed in the PSM. Using specific morpholino oligonucleotide mediated inhibition and intron probe in situ hybridisation, we find that her7 is required for initiating the expression in the posterior PSM, while her1 is required to propagate the cyclic expression in the intermediate and anterior PSM. Reporter gene constructs with the her1 upstream sequence driving green fluorescent protein (GFP) expression show that separable regulatory regions can be identified that mediate expression in the posterior versus intermediate and anterior PSM. Our results indicate that the cyclic expression is generated at the transcriptional level and that the resulting mRNAs have a very short half-life. A specific degradation signal for her1 mRNA must be located in the 5'-UTR, as this region also destabilises the GFP mRNA such that it mimics the dynamic pattern of the endogenous her1 mRNA. In contrast to the mRNA, GFP protein is stable and we find that all somitic cells express the protein, proving that her1 mRNA is transiently expressed in all cells of the PSM.

Key words: Somitogenesis, bHLH genes, mRNA stability, Enhancer analysis, Morpholino-oligonucleotide mediated knockdown

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