Mutations in Brat, Numb and Earmuff in these lineages lead to a drastic and uncontrolled expansion in the number of proliferating “tumor neuroblasts.” An important feature of the brain tumors induced by mutation of asymmetric cell division regulators in neuroblasts is that their uncontrolled overgrowth potential is maintained following transplantation of mutant brain tissue into normal hosts (Figure 5(b)). Here, NUMB is linked to brain neoplasm.