receptor tyrosine phosphatase ψ is required for Delta/Notch signalling and cyclic gene expression in the presomitic mesoderm

Segmentation in vertebrate embryos is controlled by a biochemical oscillator (`segmentation clock') intrinsic to the cells in the unsegmented presomitic mesoderm, and is manifested in cyclic transcription of genes involved in establishing somite polarity and boundaries. We show that the receptor protein tyrosine phosphatase ψ ( RPTP ψ) gene is essential for normal functioning of the somitogenesis clock in zebrafish . We show that reduction of RPTPψ activity using morpholino antisense oligonucleotides results in severe disruption of the segmental pattern of the embryo, and loss of cyclic gene expression in the presomitic mesoderm. Analysis of cyclic genes in RPTP ψ morphant embryos indicates an important requirement for RPTP ψ in the control of the somitogenesis clock upstream of or in parallel with Delta/Notch signalling. Impairing RPTPψ activity also interferes with convergent extension during gastrulation. We discuss this dual requirement for RPTP ψ in terms of potential functions in Notch and Wnt signalling.