The generation of vertebral segmental patterning in the chick embryo.

We have carried out a series of experimental manipulations in the chick embryo to assess whether the notochord, neural tube and spinal nerves influence segmental patterning of the vertebral column. Using Pax1 expression in the somite-derived sclerotomes as a marker for segmentation of the developing intervertebral disc, our results exclude such an influence. In contrast to certain teleost species, where the notochord has been shown to generate segmentation of the vertebral bodies (chordacentra), these experiments indicate that segmental patterning of the avian vertebral column arises autonomously in the somite mesoderm.

The proneural proteins Atonal and Scute regulate neural target genes through different E-box binding sites.

For a particular functional family of basic helix-loop-helix (bHLH) transcription factors, there is ample evidence that different factors regulate different target genes but little idea of how these different target genes are distinguished. We investigated the contribution of DNA binding site differences to the specificities of two functionally related proneural bHLH transcription factors required for the genesis of Drosophila sense organ precursors (Atonal and Scute). We show that the proneural target gene, Bearded, is regulated by both Scute and Atonal via distinct E-box consensus binding sites.

SUMO and transcriptional repression: dynamic interactions between the MAP kinase and SUMO pathways.

SUMO modification of proteins is being increasingly linked with transcriptional repression. We recently demonstrated that SUMO modification also downregulates the transcriptional activity of the ETS-domain transcription factor Elk-1. However, as Elk-1 becomes activated through MAP kinase-mediated phosphorylation, the SUMO modification is lost, providing an elegant molecular switch that promotes the loss of repressive activities at the same time as permitting the recruitment of coactivator proteins.