Transcriptomic analysis of mouse limb tendon cells during development.

The molecular signals driving tendon development are not fully identified. We have undertaken a transcriptome analysis of mouse limb tendon cells that were isolated at different stages of development based on scleraxis ( Scx) expression. Microarray comparisons allowed us to establish a list of genes regulated in tendon cells during mouse limb development. Bioinformatics analysis of the tendon transcriptome showed that the two most strongly modified signalling pathways were TGF-beta and MAPK. TGF-beta/SMAD2/3 gain- and loss-of-function experiments in mouse limb explants and mesenchymal stem cells showed that TGF-beta signalling was sufficient and required via SMAD2/3 to drive mouse mesodermal stem cells towards the tendon lineage ex vivo and in vitro. TGF-beta was also sufficient for tendon gene expression in late limb explants during tendon differentiation. FGF does not have a tenogenic effect and the inhibition of the ERK MAPK signalling pathway was sufficient to activate Scx in mouse limb mesodermal progenitors and mesenchymal stem cells.