CDK6 and thymus atrophy: CDK6 is predominantly expressed in hematopoietic cell types (Della Ragione et al., 1997; Chilosi et al., 1998) and loss of CDK6 in mice causes thymic atrophy and reduction in red blood cells, granulocytes, macrophages, neutrophils and platelets, as well as delayed G1 progression in lymphocytes of Cdk6−/− mice, (Malumbres et al., 2004).