Chondrogenesis from stem cell recruitment to hypertrophy by a tripotential mesoblastic cell line

Abstract

Understanding the molecular mechanisms leading embryonic mesoblastic stem cells to be recruited towards a specific lineage and thereafter to develop the corresponding differentiation programme towards its endstage is a major challenge of today’s biology. These processes clearly depend on both autonomous genetic programmes and environmental signals. The characterization of the respective contributing factors is of interest in both fundamental and medical research. The availability of pluripotent and inducible progenitor cell lines would greatly facilitate the identification of the autocrine and paracrine signals involved in the recruitment towards a given lineage and in the implementation of a complete differentiation programme. Multipotential embryonic stem cells (ES) and embryonal carcinoma cells (EC) which are able to differentiate into derivatives of the three germ layers have provided in vitro differentiation model systems 1,2 . However, molecular studies using these systems remain difficult because of the heterogeneity of differentiation and of the short life span of the differentiated daughter cells. In an attempt to isolate lineage progenitor cell lines, we have transfected multipotential embryonal carcinoma cells with an immortalizing plasmid, pK4 which contains the early genes of SV40 under the control of the promoter of the E1A adenovirus, a virus known to be active early in mouse development 3 . Upon induction of differentiation of the multipotential cells, neuroectodermal, endodermal or mesodermal precursor cell lines were immortalized. The low level of constitutive expression of the SV40 T antigen promotes immortalization of the committed progenitors while still allowing