Unsere Forschung

AG Klein

AG Reiff

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AG Klein

 

Curriculum vitae:

Thomas Klein has received his Ph.D. in Cologne 1994, where he worked on the function of the Drosophila gene klumpfuss during adult neurogenesis. He then joined the lab of William Chia at the University of Singapore for 14 month before moving on to the lab of Alfonso Martinez-Arias at the University of Cambridge, UK. 

In 1999 he moved to the University of Cologne as an independent group leader. His work covers several aspects of adult development of the fruit fly Drosophila melanogaster, in which the Notch-signalling pathway plays a role, such as wing, leg and head development as well as neurogenesis. - Thomas Klein is Professor at the Institute of Genetics in Düsseldorf since 2007.

 

Research Focus:

In the past, we investigated the role of the Notch pathway during wing development of Drosophila as a paradigm for its role in organ formation. This process takes place in an epithelial monolayer, the wing imaginal disc. This disc consists of initially undifferentiated precursor cells that become determined in a stepwise fashion. Together with several other groups, we could show that cell communication mediated by the Notch pathway is continuously required in a small stripe of cells at the dorso-ventral (D/V) boundary to orchestrate the sequential induction of genes required for pattern formation and definition of the wing field. Wing development has become one of the processes where the role of the Notch pathway is particular well understood and we are now using our knowledge of this process to investigate its regulation.

The Notch pathway is activated trough ligand induced proteolytic cleavage of Notch. The released intracellular domain (Nintra) translocates in the nucleus and activates the expression of the target genes in collaboration with Suppressor of Hairless (Su(H)). During the release of Nintra, Notch is first cleaved in the extra-cellular region close to the membrane through Kuzbanian (Kuz) in a ligand-dependent manner. The membrane anchored intermediate Notch fragment (NEXT) is immediately further processed by the y-secretase complex producing Nintra. This cleavage is ligand-independent and occurs constitutively on all NEXT-like Notch variants inserted in the plasma membrane.

The focus of our investigations is the role of the endosomal pathway during Notch signalling. This fundamental pathway has gained attention because of its involvement in the regulation of the activity of the Notch pathway as well as the degradation of the Notch receptor. Endosomal trafficking of Notch is initiated by endocytosis through addition of single ubiquitines to lysines of the intra-cellular domain of Notch. After abscission the early endosomal vesicles undergo homotypic fusion to form the early endosome (EE). Notch is located in the limiting membrane (LM) of the EE with the intracellular domain reaching into the cytoplasm. In order to be degraded, the intra-cellular domain has to be transported into the lumen of the endosome during its maturation into a late endosome (LE). This is achieved by concentrating Notch at certain regions of the LM and subsequent inside budding of this region into the lumen of the endosome. The consequence is the formation of intra-luminal vesicles (ILV) with high concentration of Notch in maturing endosomes. The ILV containing endosomes are also called multi-vesicular bodies (MVB) and their formation is controlled by the activity of four in sequence acting ESCRT protein complexes (ESCRT-0-III) (Williams and Urbe, 2007). The MVBs eventually fuse with the lysosome where the luminal content is degraded.

The main project of the lab is the characterization of the function of the tumour-suppressor-gene lethal (2) giant discs (lgd) during endosomal trafficking of the Notch-receptor. lgd encodes a member of a so far uncharacterised protein family whose hallmarks are four tandem repeats of the so far uncharacterised DM14 and a C2-domain. Loss of lgd function results in the activation of the Notch pathway in a novel, ligand-independent manner in several tissues. The observed uncontrolled activation of Notch is the cause of the observed over-proliferation of lgd mutant imaginal discs. We could show that Notch accumulates in a late endosomal compartment in lgd mutant cells due to a failure in its degradation. One main question we investigate at the moment is how Notch is activated in lgd cells.

In humans two orthologs exist which we named hLgd1 and hLgd2. hLgd2 is also known as Aki, Freud-1 or CC2D1a. A mutation in the human lgd ortholog hLgd2 has been identified as the cause of mental retardation. We have generated a conditional knock-out allele of the murine ortholog of Lgd2/Freud-1/Aki. We will use this allele to characterise the function of lgd during mammalian development.

Other projects in the lab investigate

a) other aspects of Notch trafficking through the endosmal pathway

b) the function of endocytosis during ligand-dependent signalling,

c) the role of Notch during formation of the sensory organ precursor cells.

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RG Reiff

Curriculum vitae:

Tobias Reiff obtained his PhD at the Max-Planck-Institute for brain research in Frankfurt working on the initial steps of the development of Neuroblastoma, which is the most common extracranial solid tumor in childhood and arises from precursor cells of the peripheral nervous system. He then joined the lab of Maria Dominguez in Alicante where he gained insights into molecular mechanisms of growth control and cancer in Drosophila melanogaster and established ‘ReDDM’ tracing. Since the beginning of 2017 he is an independent research group leader attached to the genetics department of Prof. Dr. Thomas Klein.

https://www.researchgate.net/profile/Tobias_Reiff

 

Our research:

In our laboratory, we aim to identify and describe new hormonal signaling pathways acting on stem cells controlling homeostasis and organ size of the adult Drosophila melanogaster intestine. The flies’ intestine has a comparably simple tissue structure consisting of only four cell types. Intestinal stem cells (ISC) that divide either symmetrically to give rise to another ISC or asymmetrically to form a so called enteroblast (EB), a progenitor cell that can either differentiate to an enteroendocrine cell (EE) or an epithelial enterocyte (EC).

To identify and trace stem cells and their derivatives in the adult intestine, we developed a new tracing method called ‘ReDDM’ (Repressible Dual Differential Marker), that in combination with cell type specific Gal4-drivers for ISC and/or EB, ReDDM enables us to follow the ‘production’ from stem cell divisions and obtain data from the whole stem cell population.

We were able to demonstrate that EB are motile entities and are able to delay their differentiation adding an important variable to how homeostasis and tissue renewal is achieved in the intestine (Antonello et al., 2015). Recently, we discovered that a complex cascade of effects elicited by a neuroendocrine hormone initiates growth and reprogramming of the female intestine as an adaptation for the higher energy demand of reproduction. Mating stimulates the release of juvenile hormone (JH) from the corpus allatum (CA), a neuroendocrine gland in the adult Drosophila brain, which in turn directly acts on JH-receptors Met (methoprene-tolerant) and gce (germ cells-expressed) in EC to enhance lipid uptake and signals to ISC to stimulate proliferation. This boost in proliferation results in an increased intestinal diameter and cell number and revealed a new control mechanism of adult organ plasticity and physiological adaptations to pregnancy through a systemic hormone (Figure 2 and Reiff et al., 2015). On a whole organism level, we could show that in parallel to local signaling cues, stem cell proliferation and hence organ size can be (re-)set through neuroendocrine signaling from the brain, by the same signal that stimulates egg production. Drosophila’s brain hereby functions as a ‘integration hub’, sending and receiving signals to monitor and control an organism´s energy and reproductive status.

 

In the future, we would like to gain deeper insight into the mechanisms controlling those adapted homeostatic conditions due to pregnancy and hormone levels in the adult fruit fly.

 

 

Lab pictures

Reiff Lab in July 2018

(FLTR: Kathrin Piasecki, Tobias Reiff, Sofie Burgmer, Denise Jassmann)

Verantwortlich für den Inhalt: E-Mail sendenProf. Dr. Thomas Klein