The Role Of XBP1 In Xenopus Laevis Pancreatic Development

XBP1 is a kind of protein that contains the basic leucine zipper structure,and it belongs to the CREB/ATF transcription factor family.It is also an important transcription factor during the unfolded protein response(UPR)induced by endoplas-mic reticulum stress(ERS).There are two forms of XBP1:the unspliced XBP1(XBP1u)and the spliced XBP1(XBP1s).When IRE la endoribonuclease activity is activated,it can splice the substrate XBPlu into the product XBPls,the XBPls splice variant then regulate a variety of UPR-related genes and maintain the homeostasis of the endoplas-mic reticulum.As a main transcription factor,XBP is participates in many physiologi-cal and pathological processes,and it plays an important role in embryonic develop-ment.Previous studies showed that mouse embryos knockout of XBP1 died between embryonic days because of pancreatic exocrine function deficiency,which indicates that XBP1 plays important roles in pancreatic development.In this study,we investi-gated XBP1 function in pancreatic development by using Xenopus laevis as a model organism since the huge numbers,fast development and easier occupations of xenopus embryos in vitro.Antisense morpholino(MO)and mRNA of XBPls were mi-croinjected into four cells stage embryos of Xenopus laevis to knockdown and overex-press XBPls.Embryos were then detected via real time quantified PCR(qRT-PCR),western blot,whole mount in situ hybridization,,immunohistochemistry.We found that expression of pancreatic progenitor cell mark gene pdx1,p48,ngn3,sox9 were down regulated in XBPlsMO injected embryos.Pancreatic exocrine and endocrine marker genes insulin and amylase were also down regulated.Through overexpression of XBPls,the phenotype and gene expression were opposite to that of XBP1sMO-injected embryos.Forkhead box protein A2(Foxa2)was identified as a modifier of early endoderm,and required for pancreas development,the function of which is sim-ilar to that of XBPls.Then Luciferase and Chip experiment showed that XBPls binds the XBPI binding site on the Foxa2 promoter.Besides,the results indicated that XBP1 was involved in pancreatic development of Xenopus laevis and may functioned by reg-ulating Foxa2.