Moreover, one of the target cyclin complexes of p27 is cyclin E-CDK2, and a transgenic over-expression mouse model has indicated that cyclin E expression in the POMC lineage is sufficient to cause cells to re-enter the cell cycle and initiate pituitary adenoma growth (Roussel-Gervais et al., 2010). This evidence concerns the gene CCNE1 and pituitary gland adenoma.