Differences in protein expression in the subcommissural organ of normal and lordotic lizards (Agama impalearis)

Lordosis, a skeletal malformation, is characterized by abnormal curvature of the vertebral column. Involvement of the subcommissural organ (SCO) in the correct development of the axial skeleton via the thread-like Reissner's fiber (RF) has been suggested. However, the functional significance of the SCO and RF in these mechanisms remains, to date, little understood. To detect eventual changes in the SCO of reptiles bearing a naturally occurring skeletal malformation, we aimed here at investigating with immunohistochemistry RF glycoprotein and immediate early gene expression in the SCO of normal and lordotic lizards. In normal lizards, RF immunoreactivity was evident in the apical and basal domains of SCO cells. In specimens derived from lordotic animals, RF-immunoreactive material filled all SCO cell portions, and numerous large droplets were observed in the basal part of the organ. Cell nuclei exhibiting immunoreactivity to the protein product of the gene c-fos were evident in basal SCO cells of lordotic animals, whereas Fos immunoreactivity was absent in the SCO of normal lizards. The changes detected in RF immunoreactivity and Fos induction in SCO cells of lordotic animals favor the occurrence of changes in the secretory activity and gene expression of SCO cells. The present data further demonstrate modifications occurring in the SCO secretory material in skeletal malformed vertebrates, and support a relationship of such changes with the malformed state of these animals.