Distinct functions for ERK1 and ERK2 in cell migration processes during zebrafish gastrulation

Kinase-activating and kinase-impaired cardio-facio-cutaneous syndrome alleles have activity during zebrafish development and are sensitive to small molecule inhibitors

The Ras/MAPK pathway is critical for human development and plays a central role in the formation and progression of most cancers. Children born with germ-line mutations in BRAF, MEK1 or MEK2 develop cardio-facio-cutaneous (CFC) syndrome, an autosomal dominant syndrome characterized by a distinctive facial appearance, heart defects, skin and hair abnormalities and mental retardation. CFC syndrome mutations in BRAF promote both kinase-activating and kinase-impaired variants. CFC syndrome has a progressive phenotype, and the availability of clinically active inhibitors of the MAPK pathway prompts the important question as to whether such inhibitors might be therapeutically effective in the treatment of CFC syndrome. To study the developmental effects of CFC mutant alleles in vivo, we have expressed a panel of 28 BRAF and MEK alleles in zebrafish embryos to assess the function of human disease alleles and available chemical inhibitors of this pathway. We find that both kinase-activating and kinase-impaired CFC mutant alleles promote the equivalent developmental outcome when expressed during early development and that treatment of CFC-zebrafish embryos with inhibitors of the FGF-MAPK pathway can restore normal early development. Importantly, we find a developmental window in which treatment with a MEK inhibitor can restore the normal early development of the embryo, without the additional, unwanted developmental effects of the drug.

Dusp-5 and Snrk-1 coordinately function during vascular development and disease

Mitogen-activated protein kinases play an integral role in several cellular processes. To regulate mitogen-activated protein kinases, cells express members of a counteracting group of proteins called phosphatases. In this study, we have identified a specific role that one member of this family of phosphatases, dual-specific phosphatase-5 (Dusp-5) plays in vascular development in vivo. We have determined that dusp-5 is expressed in angioblasts and in established vasculature and that it counteracts the function of a serine threonine kinase, Snrk-1, which also plays a functional role in angioblast development. Together, Dusp-5 and Snrk-1 control angioblast populations in the lateral plate mesoderm with Dusp-5 functioning downstream of Snrk-1. Importantly, mutations in dusp-5 and snrk-1 have been identified in affected tissues of patients with vascular anomalies, implicating the Snrk-1-Dusp-5 signaling pathway in human disease.