Gene ontology and Ingenuity Pathway Analyses (IPA) of differentially expressed genes in Pax1/Pax9 mutants. (A,B) Bar chart of enriched GO terms for down-regulated (A) and up-regulated genes (B) in E12.5 Pax1−/−Pax9−/− embryos. (C) Pax1−/−Pax9−/− embryos exhibited shortened tail phenotype compared to Pax1−/− embryos. Yellow arrows indicate tail tip. Fluorescence was seen in the IVD of E14.5 Pax1−/−Pax9+/+embryos in a regular metameric fashion. In the Pax1−/−Pax9−/− embryos, the fluorescing cells were mis-localized to the sides of the embryo with the notochord exposed in the middle (orange arrow). White arrows indicate Pax1/Pax9 lineage cells expressing EGFP in the IVD, detected by the presence of GFP expression. (D) Number of differentially expressed genes in E12.5 Pax1−/−Pax9−/− associated with the respective disease and disorder terms identified via IPA. (E) Genes differentially expressed in E12.5 Pax1−/−Pax9−/− that are associated with the respective axial skeletal defects, identified via IPA (top) and MGI phenotype (bottom). Genes down-regulated in Pax1−/−Pax9−/− respective to WT are in blue. GO, gene ontology; VC, vertebral column; IVD, intervertebral disc anlagen.