Function Study Of Leg1 In Zebrafish Liver Development

Unlike mammals and birds, teleost fish undergo external embryogenesis, and therefore their embryos are constantly challenged by stresses from their living environment. These stresses, when becoming too harsh, will cause arrest of cell proliferation, abnormal cell death or senescence. Such organisms have to evolve a sophisticated anti-stress mechanism to protect the process of embryogenesis/organogenesis. However, very few signaling molecule(s) mediating such activity have been identified.liver-enriched gene 1 (leg1) is an uncharacterized gene that encodes a novel secretory protein containing a single domain DUF781 (domain of unknown function 781) that is well conserved in vertebrates. In the zebrafish genome, there are two copies of legl, namely legla and leg1b.which are closely linked on chromosome 20.In this work, we generated two legla mutant alleles using the TALEN technique, then characterized liver development in the mutants. We show that leg1a mutant exhibits a stress-dependent small liver phenotype that can be prevented by chemicals blocking the production of reactive oxygen species. Interestingly, it appeared that UV25 treatment drastically reduced the liver size, but only subtly affected the exocrine pancreas development in the maternal-zygotic leglazju1 mutant. UV25 treatment halted liver bud formation and liver cell cycle arrest in the mutant. Further studies reveal that Leg1a binds to FGFR3 and mediates a novel anti-stress pathway to protect liver development through enhancing Erk activity. More importantly, we show that the binding of Leg1a to FGFR relies on the glycosylation at the 70th asparagine (Asn70 or N70) and mutating the Asn70 to Ala70 compromised Legl’s function in liver development.In summary, Legl plays a unique role in protecting liver development under stress conditions by serving as a secreted signaling molecule/modulator. This finding may explain the adaption of teleost fish in coping with environmental changes.