Studies of RasV12 tumours with impaired cell polarity (for example due to mutations in the tumour suppressor gene scrib) have revealed that JNK activation is critical for Mmp1 upregulation and tumour cell invasion of the VNC.24 To assess the state of JNK signalling in RasV12/pico brains, we monitored the levels of puckered, a downstream target of JNK (Martín-Blanco et al.25) using a lacZ enhancer trap (puc-lacZ). Here, SCRIB is linked to neoplasm.