Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:PKCη-C2 domain induces chondrogenic diffe-
rentiation in hMSCs The C2 domain of PKCη is thought not to affect substrate-specificity of the kinase but instead aid in its localization to membranous systems (Littler et al., 2006).
Category: