Signalling and transcription control mechanisms in myogenesis

 

Group Leader: Olivier Kassel

tel.: +49 721 608 23911 (office) or -22783 (lab)
fax: +49 721 608 23354
email: olivier.kassel∂kit.edu


 

 

Our lab focuses on the mechanisms of skeletal muscle regeneration

 

 

Research interests

 

Skeletal muscle is an extremely plastic tissue which can adapt to the changing demands of the organism. A fascinating property of skeletal muscle is its amazing capacity to repair and regenerate. However, this capacity declines with age and is affected in various pathological conditions such as certain myopathies.

Muscle regeneration relies on the process of adult myogenesis, which involves adult, resident stem cells, the so-called satellite cells. Upon muscle damage, these normally quiescent cells enter a differentiation programme, which takes them through well-defined, tightly regulated differentiation stages. Activated satellite cells first give rise to a population of proliferating transit amplifying cells, the so-called myoblasts. After a certain number of cell cycles, myoblasts stop proliferating and differentiate into committed precursor cells, the myocytes. Finally, myocytes fuse together to form new myofibres, or to damaged fibres to repair injured muscles.

The different stages of adult myogenesis

Harnessing the mechanisms of myogenesis holds great promise for future therapeutic approaches to treat muscle wasting. However, a prerequisite is a deeper understanding of the molecular mechanisms involved, in particular the specific signalling pathways and genetic programmes that ensure a proper timing of cell fate decision at the different stages of myogenesis.

To dissect the dynamics of these signalling pathways and their specific contribution to particular stages of differentiation is not trivial. These pathways are indeed frequently reiteratively used during the course myogenesis, however leading to different, stage-specific outcomes. This demands a tight temporal control of the tools used to manipulate the pathways under investigation. Furthermore, cells are not synchronised during the course of myogenesis. At any given time point, the system comprises a mixture of cells at different stages of differentiation. Therefore, a precise spatial control of the investigation tools is also required. To tackle these challenging issues, we explore the use of optogenetics and optochemical genetics as a way to manipulate key elements of signalling pathways by light with an extremely high temporal and spatial precision.

 

Experimental approaches

 

To address these questions, we use a set of complementary approaches:

Myoblasts in culture (cell line and mouse primary cells)
This approach enables us to recapitulate certain aspects of myogenesis in vitro, in particular to dissect the dynamics of signalling pathways and gene expression during differentiation.
We use a large palette of molecular biology, cell biology and chemical biology tools and methods.

      


Time lapse imaging of cultured C2C12 mouse myoblast differentiation

 

Isolated myofibres in culture
Upon isolation from mouse hind limb muscles, myofibres retain the attached satellite cells and can be cultured for days. This ex vivo approach allows the study of myogenesis in a context closer to the in vivo situation.
In particular, we use mouse genetics (genetically modified donor mouse) and chemical biology tools to dissect the early events of myogenesis.

  

 

3D reconstitution of a confocal microscopy stack showing 2 daughter cells after the 1st division of a satellite cell at the surface of a cultured, isolated mouse myofibre

 

Animal models
We study myogenesis in the context of the whole organism, using models of muscle injury / degeneration and regeneration in vivo in the mouse, in collaboration with the groups of Peter Herrlich and of Julia von Maltzahn (Leibniz Institute on Aging – Fritz Lipmann Institute, Jena) and more recently in the zebrafish, in collaboration with the group of Uwe Strähle (IBCS-BIP, KIT).

  

Cross-sections of a control (left) and a regenerating (right) mouse soleus muscle immuno-stained for laminin (green) to delineate the myofibres and counterstained with DRAQ5 to highlight the nuclei (blue).

 

Current projects

 

  • Function of the transcriptional regulator nTRIP6 in cell fate decision during myogenesis
  • Signalling pathways regulating the expression of nTRIP6 during the course myogenesis
  • Development of optogenetic tools to dissect the contribution of signalling pathways to the different stages of myogenesis
              Collaboration with the group of Barbara Di Ventura (BioQuant, University of Heidelberg)
              Project of the DFG Priority Programme “Next Generation Optogenetics: Tool Development and
              Application” (SPP1926)