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Fig. 6 | EvoDevo

Fig. 6

From: Species-specific modifications of mandible shape reveal independent mechanisms for growth and initiation of the coronoid

Fig. 6

Schematic model of coronoid process development and regulation of growth. a An as yet unknown signal induces undifferentiated mesenchyme (yellow cells) to condense to form the future dentary bone. The coronoid process is specified by the expression of Pax9 (magenta) in the condensed mesenchyme at the superior aspect of the dentary (cyan). Interaction between the dentary and the temporalis muscle results in the muscle attachment site forming labelled by Scx expression (blue) and the dentary begins to ossify. Muscle loading switches on Sox9 expression (green) in the Pax9 domain, thereby mediating the expansion of the processes. b Proposed model for the role of muscle loading in establishing variation of the coronoid process across species. When compared with omnivore and carnivores, herbivore species have smaller temporalis muscle. This results in a comparatively reduced mechanical load to the coronoid process, a reduced expression of Sox9, and consequently a smaller coronoid process. Schematised plane of section is sagittal

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