Bruce Brandhorst

Molecular Biology & Biochemistry


Embryonic development and the ECM
We are interested in the role of the extracellular matrix in embryonic development. We have found that treatment of sea urchin embryos with chlorate, a competitive inhibitor of sulfation of proteoglycans via PAPS synthase, interferes with gastrulation and radializes embryos. To a large extent, these effects can be rescued by treatment of chlorate-treated embryos with PDGF-BB, suggesting that sulfated proteoglycans are mediating signaling by this peptide factor. A subtractive hybridization approach is being used to identify genes whose expression is altered by chlorate treatment. For example, syndecan, a heparin sulfate proteoglycan core protein, is up-regulated during by chlorate treatment. Taking advantage of the urchin genome project, genes involved in PDGF signaling and the synthesis/modification of proteoglycans are being cloned with the intention of investigating their expression patterns in embryos. Their functions will be evaluated by the injection of morpholino antisense oligonucleotides into zygotes. We have also identified a protein expressed in pigment cells that binds to laminin. Secondary mesenchymal cells penetrate the basal lamina and invade the aboral ectoderm prior to differentiation as pigment cells; the laminin binding protein may be involved in this process.

Larval metamorphosis and evolution
We recently discovered evidence that a signaling pathway involving the protein chaperone Hsp90, nitric oxide (NO), and cGMP negatively regulates the initiation of metamorphosis in sea urchin and ascidian larvae. We are investigating the development of the larval nervous system, as well as the expression of nitric oxide synthase, and presence of cGMP in sea urchin pluteus larvae in an effort to understand the cellular basis for induction of metamorphosis in response to microbial biofilm. We argue that NO has a conserved role in regulating life cycle transitions in many organisms and may have permitted the evolution of marine larvae as a stage inserted into the life cycle. The resulting uncoupling of natural selection on larvae and adults, and increased fecundity of the adult, may have promoted the evolution of complex adult body forms having protective devices that appeared during the Cambrian explosion.