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Exdpf Is a Key Regulator of Exocrine Pancreas Development Controlled by Retinoic Acid and ptf1a in Zebrafish

1, 2, 1, 1, 1, 3, 1, 1,*, 1,2,*

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      Abstract

      Both endocrine and exocrine pancreatic cells arise from pancreatic-duodenal homeobox 1 (pdx1)-positive progenitors. The molecular mechanisms controlling cell fate determination and subsequent proliferation, however, are poorly understood. Unlike endocrine cells, less is known about exocrine cell specification. We report here the identification and characterization of a novel exocrine cell determinant gene, exocrine differentiation and proliferation factor (exdpf), which is highly expressed in the exocrine cell progenitors and differentiated cells of the developing pancreas in zebrafish. Knockdown of exdpf by antisense morpholino caused loss or significant reduction of exocrine cells due to lineage-specific cell cycle arrest but not apoptosis, whereas the endocrine cell mass appeared normal. Real-time PCR results demonstrated that the cell cycle arrest is mediated by up-regulation of cell cycle inhibitor genes p21Cip, p27Kip, and cyclin G1 in the exdpf morphants. Conversely, overexpression of exdpf resulted in an overgrowth of the exocrine pancreas and a severe reduction of the endocrine cell mass, suggesting an inhibitory role for exdpf in endocrine cell progenitors. We show that exdpf is a direct target gene of pancreas-specific transcription factor 1a (Ptf1a), a transcription factor critical for exocrine formation. Three consensus Ptf1a binding sites have been identified in the exdpf promoter region. Luciferase assay demonstrated that Ptf1a promotes transcription of the exdpf promoter. Furthermore, exdpf expression in the exocrine pancreas was lost in ptf1a morphants, and overexpression of exdpf successfully rescued exocrine formation in ptf1a-deficient embryos. Genetic evidence places expdf downstream of retinoic acid (RA), an instructive signal for pancreas development. Knocking down exdpf by morpholino abolished ectopic carboxypeptidase A (cpa) expression induced by RA. On the other hand, exdpf mRNA injection rescued endogenous cpa expression in embryos treated with diethylaminobenzaldehyde, an inhibitor of RA signaling. Moreover, exogenous RA treatment induced anterior ectopic expression of exdpf and trypsin in a similar pattern. Our study provides a new understanding of the molecular mechanisms controlling exocrine cell specification and proliferation by a novel gene, exdpf. Highly conserved in mammals, the expression level of exdpf appears elevated in several human tumors, suggesting a possible role in tumor pathogenesis.

      Author Summary

      The pancreas is a vital organ comprising endocrine and exocrine components. Both endocrine and exocrine cells derive from a common pool of progenitors present in the gut endoderm during embryogenesis. The molecular mechanisms regulating cell fate decisions and lineage-specific proliferation are not fully understood. In this work, we report the characterization of a novel gene, exocrine differentiation and proliferation factor (exdpf), as a regulator for exocrine cell fate and differentiation/proliferation. We show that it is a direct target of the transcription factor pancreas-specific transcription factor 1a (Ptf1a), which is expressed in progenitors that give rise to all pancreatic cell types. We find that a deficiency of exdpf results in a severe reduction of exocrine size due to defects in cell proliferation. Consistent with this finding, overexpression of exdpf leads to an increase of exocrine size and a decrease of endocrine size, suggesting a possible change in fate of the endocrine progenitors. The human ortholog of exdpf is highly conserved and its expression level appears elevated in several cancers, including hepatic and pancreatic cancers, implying a possible role in pathogenesis of these malignancies.

      Abstract

      The zebrafishexdpf, a novel regulator of pancreatic exocrine cell fate, is essential for exocrine cell differentiation and proliferation.

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      Most cited references 62

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      Stages of embryonic development of the zebrafish.

      We describe a series of stages for development of the embryo of the zebrafish, Danio (Brachydanio) rerio. We define seven broad periods of embryogenesis--the zygote, cleavage, blastula, gastrula, segmentation, pharyngula, and hatching periods. These divisions highlight the changing spectrum of major developmental processes that occur during the first 3 days after fertilization, and we review some of what is known about morphogenesis and other significant events that occur during each of the periods. Stages subdivide the periods. Stages are named, not numbered as in most other series, providing for flexibility and continued evolution of the staging series as we learn more about development in this species. The stages, and their names, are based on morphological features, generally readily identified by examination of the live embryo with the dissecting stereomicroscope. The descriptions also fully utilize the optical transparancy of the live embryo, which provides for visibility of even very deep structures when the embryo is examined with the compound microscope and Nomarski interference contrast illumination. Photomicrographs and composite camera lucida line drawings characterize the stages pictorially. Other figures chart the development of distinctive characters used as staging aid signposts.
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        Direct evidence for the pancreatic lineage: NGN3+ cells are islet progenitors and are distinct from duct progenitors.

        The location and lineage of cells that give rise to endocrine islets during embryogenesis has not been established nor has the origin or identity of adult islet stem cells. We have employed an inducible Cre-ER(TM)-LoxP system to indelibly mark the progeny of cells expressing either Ngn3 or Pdx1 at different stages of development. The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice. In addition, we find that cells expressing Pdx1 give rise to all three types of pancreatic tissue: exocrine, endocrine and duct. Furthermore, exocrine and endocrine cells are derived from Pdx1-expressing progenitors throughout embryogenesis. By contrast, the pancreatic duct arises from PDX1+ progenitors that are set aside around embryonic day 10.5 (E9.5-E11.5). These findings suggest that lineages for exocrine, endocrine islet and duct progenitors are committed at mid-gestation.
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          neurogenin3 is required for the development of the four endocrine cell lineages of the pancreas.

          In the mammalian pancreas, the endocrine cell types of the islets of Langerhans, including the alpha-, beta-, delta-, and pancreatic polypeptide cells as well as the exocrine cells, derive from foregut endodermal progenitors. Recent genetic studies have identified a network of transcription factors, including Pdx1, Isl1, Pax4, Pax6, NeuroD, Nkx2.2, and Hlxb9, regulating the development of islet cells at different stages, but the molecular mechanisms controlling the specification of pancreatic endocrine precursors remain unknown. neurogenin3 (ngn3) is a member of a family of basic helix-loop-helix transcription factors that is involved in the determination of neural precursor cells in the neuroectoderm. ngn3 is expressed in discrete regions of the nervous system and in scattered cells in the embryonic pancreas. We show herein that ngn3-positive cells coexpress neither insulin nor glucagon, suggesting that ngn3 marks early precursors of pancreatic endocrine cells. Mice lacking ngn3 function fail to generate any pancreatic endocrine cells and die postnatally from diabetes. Expression of Isl1, Pax4, Pax6, and NeuroD is lost, and endocrine precursors are lacking in the mutant pancreatic epithelium. Thus, ngn3 is required for the specification of a common precursor for the four pancreatic endocrine cell types.
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            Author and article information

            Affiliations
            [1] Key Laboratory of Cell Proliferation and Differentiation, Center of Developmental Biology and Genetics, College of Life Sciences, Peking University, Ministry of Education, Beijing, People's Republic of China
            [2] Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, Los Angeles, California, United States of America
            [3] Department of Medicine, Cedars-Sinai Research Institute, University of California, Los Angeles, Los Angeles, California, United States of America
            Wellcome Trust Sanger Institute, United Kingdom
            Author notes
            * To whom correspondence should be addressed. E-mail: bzhang@123456pku.edu.cn (BZ); shuolin@123456ucla.edu (SL)
            Contributors
            Role: Academic Editor
            Journal
            PLoS Biol
            pbio
            plbi
            plosbiol
            PLoS Biology
            Public Library of Science (San Francisco, USA)
            1544-9173
            1545-7885
            November 2008
            25 November 2008
            : 6
            : 11
            2586380
            19067490
            10.1371/journal.pbio.0060293
            08-PLBI-RA-2449R3 plbi-06-11-15
            (Academic Editor)
            Copyright: © 2008 Jiang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
            Counts
            Pages: 15
            Categories
            Research Article
            Developmental Biology
            Custom metadata
            Jiang Z, Song J, Qi F, Xiao A, An X, et al. (2008) Exdpf is a key regulator of exocrine pancreas development controlled by retinoic acid and ptf1a in zebrafish. PLoS Biol 6(11): e293. doi:10.1371/journal.pbio.0060293
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