University of Massachusetts Medical School eScholarship@UMMS GSBS Dissertations and Theses Graduate School of Biomedical Sciences 2020-01-15 The Snakeskin-Mesh Complex of Smooth Septate Junction Restricts Yorkie to Regulate Intestinal Homeostasis in Drosophila Hsi-Ju Chen University of Massachusetts Medical School Let us know how access to this document benefits ou.y Follow this and additional works at: https://escholarship.umassmed.edu/gsbs_diss Part of the Cell Biology Commons, and the Genetics Commons Repository Citation Chen H. (2020). The Snakeskin-Mesh Complex of Smooth Septate Junction Restricts Yorkie to Regulate Intestinal Homeostasis in Drosophila. GSBS Dissertations and Theses. https://doi.org/10.13028/ 0r15-ze63. Retrieved from https://escholarship.umassmed.edu/gsbs_diss/1059 This material is brought to you by eScholarship@UMMS. It has been accepted for inclusion in GSBS Dissertations and Theses by an authorized administrator of eScholarship@UMMS. For more information, please contact [email protected]. The Snakeskin-Mesh Complex of Smooth Septate Junction Restricts Yorkie to Regulate Intestinal Homeostasis in Drosophila A Dissertation Presented by Hsi-Ju Chen Submitted to the Faculty of the University of Massachusetts Graduate School of Biomedical Sciences, Worcester In partial fulfilment of the requirement for the requirements for the Degree of Doctor of Philosophy November 19, 2019 TABLE OF CONTENTS ABSTRACT CHAPTER I...................................................................................................... i INTRODUCTION................................................................................................. 1 The importance to maintain the health of the digestive tract............................... 1 The Hippo pathway.............................................................................................. 4 1. The core kinase of the Hippo signaling pathway and its conservation......................... 4 Drosophila ..................................................................................................... 4 Mammalian..................................................................................................... 10 2. Versatile upstream signals to regulate the Hippo signaling pathway............................ 15 Cell polarity.................................................................................................... 15 Cell-cell contact: cytoskeleton and mechanotransduction........................................ 22 Metabolite....................................................................................................... 24 Soluble factors................................................................................................. 25 (3) Crosstalk with other signaling to regulate ISCs behavior.......................................... 26 Mammalian intestine........................................................................................ 26 Drosophila midgut........................................................................................... 30 The Cell Junctions................................................................................................ 35 (1) The constituents of Vertebrates epithelial cell junctions........................................... 35 Tight junction................................................................................................... 35 Adherens junction............................................................................................. 41 Desmosome..................................................................................................... 42 (2) The cell junctions of the invertebrates exhibit comparable functions........................... 49 (3) The mechanisms that cell junctions adopt to regulate cell growth............................... 53 CHAPTER II..................................................................................................... ii ABSTRACT......................................................................................................... 57 INTRODUCTION............................................................................................... 58 RESULTS............................................................................................................. 61 Loss of smooth septate junction proteins in EBs leads to ISC proliferation..................... 61 Yorkie and Upd3 mediate the growth after loss of Ssk or Mesh.................................... 72 Ssk and Mesh expression and function are initiated in EBs to produce Upd3 for ISC proliferation..........................................................................................................78 Ssk and Mesh also have functions in ECs to regulate Yorkie-Upd3 and thereby ISC proliferation......................................................................................................... 90 The Ssk-Mesh complex are required for the co-localization with other junction proteins in ECs.....................................................................................................................98 Loss of Ssk and Mesh in EBs and ECs lead to different degrees of gut leakiness and animal viability..............................................................................................................105 Ssk and Mesh form a complex with and restrict the activity of Yki..............................109 DISCUSSION......................................................................................................115 MATERIALS AND METHODS ........................................................................118 TABLE 1.............................................................................................................124 ACKNOWLEDGMETNS.................................................................................. 130 CHAPTER III.................................................................................................135 DISCUSSION.....................................................................................................131 What lies between the smooth septate junctions and Yki?...........................................131 Not just glue, the smooth septate junctions serve as a signaling transduction center...........133 Two are not enough. Bicellular and tricellular junctions cooperatively strength the structure and integrity of the epithelia...................................................................................135 The roles of septate/tight junction protein in ISC proliferation and tissue homeostasis....137 Ssk and Mesh exhibit conserved functions in the insecta, but their vertebrate counterparts are multifaceted...................................................................................................141 Future direction & prospective application...............................................................143 REFERENCE................................................................................................ 148 FIGURE LIST Figure A. The activation mechanisms in the Hippo kinase cascade.....................9 Figure B. Multiple signals are integrated to regulate the Hippo pathway.............9 Figure C. The Hippo pathway coordinates multiple signals to regulate the activity of YAP/TAZ .........................................................................................................14 Figure D. The components of cell junctions are conserved..................................21 Figure E. The structure and the cell lineages of the mammalian intestine.......................27 Figure F. The Drosophila midgut..........................................................................31 Figure G. Epithelial niche and conserved signaling regulate ISC division and cell fate to control homeostasis....................................................................................................32 Figure H. Schematic representation of the basic structural components of tight junctions and adherens junctions...........................................................................40 Figure I. Schematic representation of the structural components of Desmosome........43 Figure J. Proposed models........................................................................................147 Figure 1. Loss of smooth septate junction proteins in EBs leads to ISC proliferation...............62 Figure 2. Ssk and mesh loss of function mutant clones increase proliferation majorly through an ISC-non-autonomous mechanism.................................................................................66 Figure 3. Ssk and mesh mutant neither skew the asymmetric division nor affect the differentiation of ISCs................................................................................................70 Figure 4. Upd3 is secreted out to mediate the growth after loss of Ssk or Mesh......................73 Figure 5. Yki regulates the Upd3 expression to control the growth after loss of Ssk or Mesh....76 Figure 6. Ssk and Mesh expression and function are initiated in EBs.................................80 Figure 7. Loss of Ssk or Mesh within EBs does not affect the differentiation into ECs.........85 Figure 8. Loss of Ssk or Mesh within ISCs did not show an increased proliferation phenotype.................................................................................................................86 Figure 9. Loss of Ssk or Mesh function initiates the expression of Upd3 within EBs............87 Figure 10. Ssk and Mesh also have