PTEN and neoplasm: However, the generation of Pten knock-in mice harbouring the PtenG129E mutation, with loss of PTEN lipid phosphatase function only, and the PtenC124S mutation, with loss of PTEN lipid and protein phosphatase activity, has shown that PTEN regulation of PtdIns(3,4,5)P3 levels is the only essential PTEN function during embryonic development and in tumour initiation [42].