The Role Of IRE1α In Xenopus Pancreas Development

Pancreas is a digestive organ developed from endoderm, and panceasr involvedin carbohydrate, lipid and protein metabolism. The development of the pancreas is adynamic continuous process, regulated by multiple signaling pathways andtranscription factors. Inositol-requiring enzyme1α is a transmembrane protein locatedon the endoplasmic reticulum, is one of the three ER stress signaling sensors. Whenendoplasmic reticulum stress happens, IRE1α can sense ERS and pass the signal forthe unfolded protein response. Previous studies had found that IRE1α highlyexpressed in the mouse pancreas and also in Xenopus, suggested that IRE1α may beinvolved in the pancreas development. However, the role of IRE1α in the pancreasdevelopment is not clear. This study uses Xenopus as a model animal to investigatethe of IRE1α genes function in Xenopus pancreas development. We usedmicroinjection of IRE1α mRNA into four stage embryos of Xenopus and found thatoverexpression of the IRE1α mRNA had no significant effection on the Xenopuslaevis pancreas development. Injected specific antisense oligonucleotides morpholino(MO) to knock down the IRE1α gene expression, the Xenopus laevis embryos wereseverely deformed and via in situ hybridization we found that the pancreas endocrinegene insulin glucagon and exocrine gene amylase were all reduced significantly.Gastric marker gene Sfrp5liver specific gene Hex have no significantly change, andthat the pancreas precursor cell marker gene Pdx1P48and Ngn3were reduced, butthe endoderm marker gene Xsox17α and the mesoderm marker gene Xbra were notaffected when IRE1α was blocked. We isolated the animal caps from the St.9embryos otrof Xenopus and cultured them in vitro in order to set a model for the induction of the pancreatic tissue development, and we found that these animal caps,evolved from embryos coinjected with IRE1α at4cell stage, failed to be induced intopancreatic tissue, negative signals of insulin in in situ hybridization trails, but thecontrol animal caps evolved from the normal embryos showed obviously positivesignals of insulin. We also contructed the domainant negative mutant IRE1ΔC ofwhich was the construct of IRE1α deleted of its C-terminal protein(kinase-endonuclease domain), and found these embryos injected with IRE1ΔC failedto show insulin signal in in situ hybridization. Finally we also found that theseembryos injected with XBP1MO at4cell stage, failed to show both insulin andamylase signals, resembling that of the embryos injected with IRE1α MO, whichindicated that IRE1α may functioned through the IRE1-XBP1pathway.