Ofd1 is required in limb bud patterning and endochondral bone development

Oral-facial-digital type I (OFDI) syndrome is an X-linked male lethal developmental disorder. It is ascribed to ciliary dysfunction and characterized by malformation of the face, oral cavity, and digits. Conditional inactivation using different Cre lines allowed us to study the role of the Ofd1 transcript in limb development. Immunofluorescence and ultrastructural studies showed that Ofd1 is necessary for correct ciliogenesis in the limb bud but not for cilia outgrowth, in contrast to what was previously shown for the embryonic node. Mutants with mesenchymal Ofd1 inactivation display severe polydactyly with loss of antero-posterior (A/P) digit patterning and shortened long bones. Loss of digit identity was found to be associated with a progressive loss of Shh signaling and an impaired processing of Gli3, whereas defects in limb outgrowth were due to defective Ihh signaling and to mineralization defects during endochondral bone formation. Our data demonstrate that Ofd1 plays a role in regulating digit number and identity during limb and skeletal patterning increasing insight on the functional role of primary cilia during development.