Homepage bandeau_genéral
  Csd


  Director : Shahragim TAJBAKHSH (shaht@pasteur.fr )


  abstract

 

The principal interest of the laboratory is centered how stem cells are maintained, and how their fates become restricted to specific lineages during. Our principal model of choice is skeletal muscle development in the embryo, post-natally and in the adult. We are using a genetic approach in the mouse, both by transgenesis and knock-ins, to localise, isolate, and characterise these stem cells in somites of the embryo, in the developing limbs, and in adult skeletal muscle satellite cells.



  report

cale

The principal interest of the laboratory is centered how stem cells are maintained, and how their fates become restricted to specific lineages during. Our principal model of choice is skeletal muscle development in the embryo, post-natally and in the adult. We are using a genetic approach in the mouse, both by transgenesis and knock-ins, to localise, isolate, and characterise these stem cells in somites of the embryo, in the developing limbs, and in adult skeletal muscle satellite cells.

Several years ago we showed that in the absence of Myf5, muscle progenitor cells remained multipotent and were capable of changing their fate in the embryo when located ectopically. This finding coupled with the fact that Myf5 expression marks post-natal satellite cells which have stem cell-like properties, incited us to create various knock-in alleles at the Myf5 locus. Our repertoire includes nlacZ, MyoD, and GFP. In addition to investigating skeletal muscle biology, these mice are designed to allow the molecular and cellular characterisation of skeletal muscle stem cells. Further, new Myf5 alleles which do not provoke distal rib phenotypes (see below) have been also generated in order to investigate Myf5 function, notably in satellite cells of young and older animals.

Using double mutant mice, we showed previously that the paired/homeodomain gene Pax3 and the transcription factor Myf5 act upstream of Myod. Other genes which are implicated in early skeletal muscle development are the receptor tyrosine kinase, c-met, and the ortholog of Pax3, Pax7. The role that c-met plays within this genetic network is being examined in c-met/Myf5 double mutant mice. Pax7 plays a key role in post-natal satellite cell specification - we are also investigating the role of this gene, in combination with Myf5, in adult satellite cells.

We are investigating muscle stem cell function using multiple strategies. First, a biased approach involves examining the potential role of asymmetric cell divisions in maintaining muscle stem cells and producing lineage committed differentiated muscle cells, in the embryo and adult. A second approach involves preparing cDNA banks from FACs sorted cells derived from heterozygous and homozygous Myf5-GFP knock-in mice. The transcriptional contents of these banks will be evaluated on microarrays in the hope of identifying new markers for muscle stem cells, in particular those which maintain or provoke their proliferation/differentiation. We expect that this screen would also identify Myf5 and Myod target genes.

One of our objectives is to use combinations of Cre/loxP, FLP/frt, inducible Cre and the tetracycline system to ask precise questions concerning stem cell biology. Many of these knock-ins are being generated at the Myf5 locus. For example, an inducible diphtheria toxin gene is designed to perform cell ablations at precise locations in the embryo and adult — this being dictated by the specific Cre employed. Some of these mutations do not result in the absence of distal ribs as was the case with our Myf5nlacZ/nlacZ mutant. One of these mutants, Myf5dCT (containing a floxed neomycin gene), results in the truncation of the C-terminal transactivation domain of Myf5. Although Myf5dCT/dCT mice are alive and fertile, the early myotome is missing. We have therefore uncoupled the skeletal muscle defects due to Myf5, from the rib phenotype which implicates the interplay of another nearby gene for distal rib formation. Our collection of mutants has revealed a critical developmental window when distal rib development takes place, and we are now investigating the possibility that a nearby gene, perhaps Mrf4, is implicated in distal rib development.

Photos : Where are skeletal muscle stem cells located and how are they maintained?

During early embryonic development, skeletal muscle stem cells in the body proper are located in the somites, transitory segmented units located bilaterally along the neural tube. They are subsequently localised in the dermomyotome epithelium and, during foetal stages, most likely distributed among the skeletal muscle masses. At post-natal stages and in the adult, satellite cells represent a potential stem cell population. These satellite cells can be genetically identified and distinguished from myonuclei using the Myf5nlacZ/+ knock-in mouse.



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
   

Lina Duchossoy (Ph.D)
Barbara Gayraud-Morel (Ph.D)
Vasily Shinin (Ph.D.)

 

Danielle Gomés (Technician, Pasteur)


filet

Page Top research Institut Pasteur homepage

If you have problems with this Web page, please write to rescom@pasteur.fr.