In key C. elegans adult tissues, the lin-4 miRNA may act to suppress the translation of lin-14, preventing lin-14 from affecting the transcription of a yet unidentified factor that regulates or interacts with the daf-2 insulin/ IGF-1 pathway. By demonstrating that lin-4 and lin-14, two key temporal regulators of development, also influence the rate of aging, we provide support for the theory that life span is affected by an innate, programmed timing mechanism. However, our data are also consistent with an alternative theory of aging, antagonistic pleiotropy, which posits that genes with primary roles in development can later secondarily influence life span (27). miRNAs are important regulators of development, apoptosis, and metabolism (28-31), and our work demonstrates that a miRNA can regulate aging, possibly through the insulin-like signaling pathway. It is possible that the mammalian lin-4 miRNA homologs, the miR-125 family, may regulate processes responsible for lifespan determination in vertebrates.

We examined the role of angiogenesis and the need for receptor signaling using chemical inhibition of the vascular endothelial growth factor receptor in the adult zebrafish tail fin. Using a smallmolecule inhibitor, we were able to exert precise control over blood vessel regeneration. An angiogenic limit to tissue regeneration was determined, as avascular tissue containing skin, pigment, neuronal axons and bone precursors could regenerate up to about 1 mm. This indicates that tissues can regenerate without direct interaction with endothelial cells and at a distance from blood supply. We also investigated whether the effects of chemical inhibition could be enhanced in zebrafish vascular mutants. We found that adult zebrafish, heterozygous for a mutation in the critical receptor effector phospholipase Cγ1, show a greater sensitivity to chemical inhibition. This study illustrates the utility of the adult zebrafish as a new model system for receptor signaling and chemical biology.In the postgenomic era, assigning gene function and delineating signaling pathways require the combined effort of multiple disciplines and approaches. The use of chemical probes has immense potential in examining biological processes and developing specific therapeutic compounds. On the biological side, these goals can be achieved through the appropriate use of model systems. In vitro and cell-based assays have been widely used for drug discovery and chemical library screening 1-3 . Whole organism approaches are also possible using yeast, worms, flies or zebrafish embryos 4,5 . Of these, the zebrafish, as a vertebrate organism, has reasonable counterparts to many mammalian organs, tissues and cell types. As such, it affords an opportunity to investigate more complex biological processes 5 . The transparency of the zebrafish embryo has facilitated visual scoring of phenotypic defects. Thus, it has been used extensively for developmental biology and genetics, and in the last few years as a new model Correspondence should be addressed to J.C. (joanne.chan@childrens.harvard.edu).. 6 These authors contributed equally to this work. COMPETING INTERESTS STATEMENT The authors declare competing financial interests (see the Nature Chemical Biology website for details).Note: Supplementary information is available on the Nature Chemical Biology website. NIH Public Access Author ManuscriptNat Chem Biol. Author manuscript; available in PMC 2006 August 9. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript for chemical biology 4,5 . However, tissue growth and differentiation are very different in an embryo versus in an adult animal. Embryonic development involves precise coordination of genetic programs that allow the building of a whole organism from a single cell. Therefore, chemical genetic analysis in embryos is dictated by the timing of developmental events. In an adult animal, organ maintenance and cellular needs are different, with turnover and repair being important. Another crucial consideration in developing therape...

Zebrafish fin regeneration requires the formation and maintenance of blastema cells. Blastema cells are not derived from stem cells but behave as such, because they are slow-cycling and are thought to provide rapidly proliferating daughter cells that drive regenerative outgrowth. The molecular basis of blastema formation is not understood. Here, we show that heat-shock protein 60 (hsp60) is required for blastema formation and maintenance. We used a chemical mutagenesis screen to identify no blastema (nbl), a zebrafish mutant with an early fin regeneration defect. Fin regeneration failed in nbl due to defective blastema formation. nbl also failed to regenerate hearts. Positional cloning and mutational analyses revealed that nbl results from a V324E missense mutation in hsp60. This mutation reduced hsp60 function in binding and refolding denatured proteins. hsp60 expression is increased during formation of blastema cells, and dysfunction leads to mitochondrial defects and apoptosis in these cells. These data indicate that hsp60 is required for the formation and maintenance of regenerating tissue.blastema ͉ regeneration ͉ zebrafish ͉ genetics ͉ stress response