Fig. 8. Sox5 and Sox6 control essential steps in the notochord and chondrocyte differentiation pathways. Chondrocytes and notochord cells progress through four major differentiation steps during development. Major transcription factors known to control one or several of these steps are indicated. Biochemical (Shh and noggin) and physical (mechanical pressure) interactions occur between the two lineages at several steps. See the end of Discussion for details.