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. / <p>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.</p>

<p>The insulin-like 3 peptide is autocrine/paracrine insulin-related hormone with a size of approximately 6kDa [1]. It mediates through a leucine richG-coupled receptor named LGR8. INSL3 is mainly expressed in human Leydig cells and is directly responsible for migration of the testis during the pre-natal period in maledevelopment. [2]</p><p>INSL3 mRNA has recently been verified in human platelets whereas no mRNA has been detected for LGR8 (by Sanofi-Aventis GmbH in Frankfurt,Germany), indicating that INSL3 might be released through paracrine functions at sites of platelet adhesion and aggregation upon a vascular injury.Furthermore, has activated platelets been shown to translate essential proteins upon activation, in a term called “signal-dependent protein synthesis”.The B-Cell lymphoma-3 protein (BCL-3) is an example of such a protein [3], and there is a possibility that INSL3 might be also.</p><p>In this thesis we wanted to detect the relaxin- like peptide 3 hormone (INSL3). (Its function, location and the timeframe of its release, when/if it issecreated in stimulated platelets).The source of platelet-derived INSL3 can be found with Western blotting and Enzyme immunoassay.</p><p>Detection of the insulin-like 3 peptide in human platelets turned out to be a difficult challenge due to the small amount of INSL3 secretion uponplatelet activation; hence the total amount of INSL3 produced might be below detection limit.</p>

The insulin-like 3 peptide is autocrine/paracrine insulin-related hormone with a size of approximately 6kDa [1]. It mediates through a leucine richG-coupled receptor named LGR8. INSL3 is mainly expressed in human Leydig cells and is directly responsible for migration of the testis during the pre-natal period in maledevelopment. [2] INSL3 mRNA has recently been verified in human platelets whereas no mRNA has been detected for LGR8 (by Sanofi-Aventis GmbH in Frankfurt,Germany), indicating that INSL3 might be released through paracrine functions at sites of platelet adhesion and aggregation upon a vascular injury.Furthermore, has activated platelets been shown to translate essential proteins upon activation, in a term called “signal-dependent protein synthesis”.The B-Cell lymphoma-3 protein (BCL-3) is an example of such a protein [3], and there is a possibility that INSL3 might be also. In this thesis we wanted to detect the relaxin- like peptide 3 hormone (INSL3). (Its function, location and the timeframe of its release, when/if it issecreated in stimulated platelets).The source of platelet-derived INSL3 can be found with Western blotting and Enzyme immunoassay. Detection of the insulin-like 3 peptide in human platelets turned out to be a difficult challenge due to the small amount of INSL3 secretion uponplatelet activation; hence the total amount of INSL3 produced might be below detection limit.

Relaxin and insulin-like peptide-3 (INSL3) are closely related reproductive hormones that are derived from a common ancestor. Relaxin was initially named for its ability to relax the pubic symphysis in pregnant guinea pigs at parturition. Since then relaxin has been found to be involved in many physiological processes based on its ability to stimulate the breakdown and remodeling of collagen fibers. INSL3 is also known as Leydig insulin-like hormone and the relaxin-like factor, and is produced by the Leydig cells in the testis, the thecal and luteal cells of the ovary, the thyroid, placenta and mammary gland. INSL3 induces transabdominal testicular descent by stimulating the development of the gubernacular ligament, which subsequently swells and contracts to pull the fetal testes towards the inguinal wall. In adults however, evidence suggests that INSL3 is involved in reproductive function, acting to promote the survival of male and female germ cells.

科学研究費補助金 研究種目:一般研究(C) 課題番号:04640655 研究代表者:溝口 明 研究期間:1992-1994年度