Pie chart depicting gene ontology (GO) analysis of proteins identified in the murine intervertebral disc. Representation of the distribution of proteins according to their molecular function as (A) biological process, (B) molecular function, (C) cellular component, and (D) protein class. Categorizations were based on information provided by the PANTHER classification system (www.pantherdb.org; v9.0). A total of 10 groups for molecular function, 12 groups for biological process, 7 cellular components, and 27 protein classes were detected. Further analysis of the intracellular classification revealed that the majority of proteins were characterized as cytoskeletal, followed by cytoplasmic, organelle and protein-transport ATP synthase complex.