Although E18.5 Nes-Cre Wt1co kidneys do not show histologically recognizable muscle tissue, the recognition of an early muscle-differentiation signature just a week after loss of Wt1 could suggest that this is a direct effect of this loss that does not require the activating mutations in CTNNB1 that are found in the majority of these tumours. The gene discussed is CTNNB1; the disease is neoplasm.