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Morphological and functional effects of insulin signaling and the bHLH transcription factor Dimmed on different neuron types in Drosophila
Stockholm University, Faculty of Science, Department of Zoology.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In Drosophila, the insulin signaling pathway is at the interface between dietary conditions and control of growth and development, reproduction, stress responses and life span. Eight insulin like peptides (Dilp1-8), an insulin tyrosine kinase receptor (dInR) and its downstream components, as well as a relaxin-like receptor type (Lgr3) form the core of this signaling. Here we showed that the dInR mediates post-mitotic cell growth specifically in about 300 peptidergic neurons expressing the basic helix loop helix (bHLH) transcription factor Dimmed (Paper I).  Overexpression of dInR in Dimm positive neurons leads to increased size of cell body, Golgi apparatus and nucleus, whereas dInR knockdown causes an opposite effect. Manipulation of downstream components of insulin signaling induces similar changes in Dimm positive neurons. This mechanism is nutrient dependent. In Paper II, we further investigate the relation between Dimmed and dInR for regulation of cell growth. Coexpressing Dimm and dInR in a range of Dimm negative neurons results in increased cell size in both larval and adult stages. We provide further evidence that dInR regulates cell growth in a Dimm dependent manner and that DILP6 from glia cells is involved in this regulation. In addition, we find that Dimm alone is capable of triggering cell growth in certain neuron types at different developmental stages. Furthermore, ectopic Dimm alone can block apoptosis.  Dimm is a known master regulator of peptidergic cell fate. In paper III we find that ectopic expression of Dimm in Dimm negative motor neurons results in transformation the neurons towards a neuroendocrine phenotype. They acquire enlarged axon terminations and boutons, lose both pre- and postsynaptic markers, and display diminished levels of wingless and its receptor dFrizzled. Furthermore they show increased expression of several Dimm targets. Finally, combined ectopic Dimm and dInR expression gives rise to stronger phenotypes. In paper IV we studied another DILP possibly involved in growth regulation, the under-investigated DILP1. We generated Dilp1-Gal4 lines and anti DILP1 antibodies and found that DILP1 is transiently expressed in brain insulin producing cells (IPCs) from pupal stages to newly hatched adult flies. Diapausing virgin female flies display a high expression level of dilp1/DILP1 over at least 9 weeks of adult life. DILP1 expression is also correlated with the persistence of larval/pupal fat body and its expression is regulated by other DILPs and short neuropeptide F (sNPF). Flies mutant in dilp1 display increased food intake, but decreased stress resistance and life span. We found no obvious role of DILP1 in growth regulation.

Place, publisher, year, edition, pages
Stockholm University, 2016. , 41 p.
Keyword [en]
insulin signaling, Dimm, neuropeptide, insulin receptor, insulin-like peptide, drosophila
National Category
Natural Sciences Biological Sciences
Research subject
Functional Zoomorphology
Identifiers
URN: urn:nbn:se:su:diva-125941ISBN: 978-91-7649-283-3 (print)OAI: oai:DiVA.org:su-125941DiVA: diva2:896229
Public defence
2016-02-26, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2016-02-03 Created: 2016-01-20 Last updated: 2017-02-20Bibliographically approved
List of papers
1. Insulin/IGF-Regulated Size Scaling of Neuroendocrine Cells Expressing the bHLH Transcription Factor Dimmed in Drosophila
Open this publication in new window or tab >>Insulin/IGF-Regulated Size Scaling of Neuroendocrine Cells Expressing the bHLH Transcription Factor Dimmed in Drosophila
2013 (English)In: PLOS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 9, no 12, e1004052Article in journal (Refereed) Published
Abstract [en]

Neurons and other cells display a large variation in size in an organism. Thus, a fundamental question is how growth of individual cells and their organelles is regulated. Is size scaling of individual neurons regulated post-mitotically, independent of growth of the entire CNS? Although the role of insulin/IGF-signaling (IIS) in growth of tissues and whole organisms is well established, it is not known whether it regulates the size of individual neurons. We therefore studied the role of IIS in the size scaling of neurons in the Drosophila CNS. By targeted genetic manipulations of insulin receptor (dInR) expression in a variety of neuron types we demonstrate that the cell size is affected only in neuroendocrine cells specified by the bHLH transcription factor DIMMED (DIMM). Several populations of DIMM-positive neurons tested displayed enlarged cell bodies after overexpression of the dInR, as well as PI3 kinase and Akt1 (protein kinase B), whereas DIMM-negative neurons did not respond to dInR manipulations. Knockdown of these components produce the opposite phenotype. Increased growth can also be induced by targeted overexpression of nutrient-dependent TOR (target of rapamycin) signaling components, such as Rheb (small GTPase), TOR and S6K (S6 kinase). After Dimm-knockdown in neuroendocrine cells manipulations of dInR expression have significantly less effects on cell size. We also show that dInR expression in neuroendocrine cells can be altered by up or down-regulation of Dimm. This novel dInR-regulated size scaling is seen during postembryonic development, continues in the aging adult and is diet dependent. The increase in cell size includes cell body, axon terminations, nucleus and Golgi apparatus. We suggest that the dInR-mediated scaling of neuroendocrine cells is part of a plasticity that adapts the secretory capacity to changing physiological conditions and nutrient-dependent organismal growth.

National Category
Genetics
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-101253 (URN)10.1371/journal.pgen.1004052 (DOI)000330533300070 ()
Funder
Swedish Research Council, 621-2010-5742
Note

AuthorCount:3;

Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2017-12-05Bibliographically approved
2. Multiple effects of the transcription factor Dimmed and the insulin receptor on growth and differentiation vary among neuron types and developmental stages in Drosophila
Open this publication in new window or tab >>Multiple effects of the transcription factor Dimmed and the insulin receptor on growth and differentiation vary among neuron types and developmental stages in Drosophila
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-125119 (URN)
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2016-01-21Bibliographically approved
3. Transcriptional reorganization of Drosophila motor neurons and their muscular junctions towards a neuroendocrine phenotype by the bHLH protein DIMM
Open this publication in new window or tab >>Transcriptional reorganization of Drosophila motor neurons and their muscular junctions towards a neuroendocrine phenotype by the bHLH protein DIMM
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-125115 (URN)
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2016-01-21Bibliographically approved
4. Drosophila insulin-like peptide 1 (DILP1) is transiently expressed and plays roles during non-feeding stages and reproductive dormancy
Open this publication in new window or tab >>Drosophila insulin-like peptide 1 (DILP1) is transiently expressed and plays roles during non-feeding stages and reproductive dormancy
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-125117 (URN)
Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2016-01-26Bibliographically approved

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