Scientific Report 2003-2004 - Cleveland Clinic Lerner Research ...

ORTHOPAEDICBIOLOGY ANDBIOENGINEERINGThe Department of Biomedical EngineeringGenetic Basis of Cell Fate Determinationand DifferentiationTHE LEFEBVRELABORATORYPOSTDOCTORAL FELLOWSSrijeet Mitra, Ph.D.Patrick Smits, Ph.D.Lai Wang, MD, Ph.D.RESEARCH TECHNICIANSPeter Dy, B.S.Michael Patrick, B.S.COLLABORATORSMatthew Warman, M.D. 1Clemencia Colmenares, Ph.D. 2Paul Fox, Ph.D. 31Dept. of Genetics, CaseWestern Reserve Univ.,Cleveland, OH2Dept of Cancer Biol., CCF3Dept of Cell Biol., CCFDeptofCelBiology, Cleveland Clinic FoundationOur main objectives are to identify andcharacterize genetic mechanisms thatvertebrates use to generate the largepanel of their highly different and specialized celltypes. Commitment and differentiation of stemcells towards specific lineages are multi-stepprocesses involving various types of regulatorymolecules. Our laboratory focuses on thedevelopment of the skeleton and hematopoieticsystem and on transcription factors belonging tothe Sox family that are involved in theseprocesses. We use molecular biology, cell biology,and mouse genetic engineeringapproaches.Sox transcriptionfactors are a family of 20proteins in mice and humans.Their common feature is anSry-related HMG boxdomain. Upon binding tospecific DNA sequences, thisdomain induces a strong bendof the DNA helix, a propertythat may allow Sox proteinsto facilitate the assembly ofcell-specific transcriptionalcomplexes. In addition tothe HMG box domain,several Sox proteins harbor atransactivation or atransrepression domain. Theprecise molecular roles ofSox transcription factorsremain largely unknown.Each Sox gene has a uniquespatial and temporalexpression pattern in vivo, such that each isexpressed in one or a few distinct cell types.Studies of mouse and human mutants haveuncovered critical roles for a handful of Soxgenes in determining cell fate and differentiationin specific lineages, but the roles of most SoxLefebvre, V., Li, P., and B. de Crombrugghe (1998) A new long form of Sox5 (L-Sox5), Sox6 and Sox9 are co-expressed in chondrogenesis and cooperatively activatethe type II collagen gene. EMBO J. 17:5718-5733.Smits, P., Li, P., Mandel, J., Zhang, Z., Deng, J.M., Behringer, R.R., de Crombrugghe,B., and V. Lefebvre (2001) The transcription factors L-Sox5 and Sox6 are essentialfor cartilage formation. Developmental Cell 1:277-290.de Crombrugghe, B., Lefebvre, V., and K. Nakashima (2001) Regulatory mechanismsin the pathways of cartilage and bone formation. Curr. Opin. Cell Biol.13:721-727.Lefebvre, V. (2002). Toward understanding the functions of the two highly relatedSox5 and Sox6 genes. J. Bone Miner. Metab. 20:121-130.Smits, P., and V. Lefebvre (2003) L-Sox5 and Sox6 are required for notochord extracellularmatrix sheath formation, notochord cell survival and development of thenucleus pulposus of intervertebral discs (2003). Development 130, 1135-1148.Véronique Lefebvre, Ph.D.genes remain to be uncovered. Our laboratoryworks to uncover new molecular and cellularroles of Sox factors.We currently pursue the study of Sox5 andSox6. These two highly identical genes are coexpressedin chondrocytes and notochord cells.We recently showed that chondrocytes are unableto overtly differentiate in mouse embryos lackingboth Sox5 and Sox6. The cells express all majorcartilage extracellular matrix genes at reduced orundetectable level, hardly proliferate, and matureaberrantly. Cartilage elements remain rudimentaryand are precociously replacedby bone. Embryos die beforebirth with a very severeskeletal dysplasia. Morerecently, we found that Sox5and Sox6 are also required innotochord cells (Smits andLefebvre, 2003). Theycontrol notochord extracellularmatrix formation and cellsurvival, and the transformationof the notochord intothe nucleus pulposus cores ofintervertebral discs. Hence,Sox5 and Sox6 control twocell types that have majorroles in the development ofthe vertebrate skeleton.Current projects are tofurther define the roles ofSox5 and Sox6 in vivo. Weare aiming at identifying thegenes directly targeted by theSox5 and Sox6 proteinproducts, and at determiningthe mode of action of these proteins on targetgenes. We are collaborating with Dr. MatthewWarman to identify human diseases caused bymutations in SOX5 or SOX6 and with Drs.Clemencia Colmenares and Paul Fox to characterizenon-skeletal phenotypes in Sox5 and Sox6mutant mice. New projects are being developedto study the roles of other Sox genes in variousother aspects of skeleton development, and todetermine the roles of Sox genes in the specificationof hematopoietic stem cells toward distinctblood cell lineages.38