GZMM and retinoblastoma: In addition, compared to that in the egg cell where low levels of maintenance DNA methyltransferases including MET1 and CMT3, and high levels of de novo DNA methyltransferases (DRM1/2) are detected, the central cell keeps barely detectable levels of MET1 and CMT3 and low levels of DRM1/2 (Jullien et al., 2012), where MET1 was proposed to be repressed in the central cell via a Retinoblastoma pathway (Jullien et al., 2008).