Fibroblasts isolated from tuberous sclerosis patients, lacking a protein known as TSC2, stimulate hair follicles when grafted onto the skin of mice. The grafts also show features of benign tumours and these findings suggest that cells devoid of TSC2 induce abnormal proliferation or growth in normal tissue, known as a harmatoma.
Tuberous sclerosis patients carry mutations in the genes TSC1 or TSC2, leading to inactivation of one copy of the gene. These patients have benign harmatoma tumours that are thought to arise when cells accumulate additional mutations in TSC1 or TSC2 genes. Thomas Darling and colleagues show in Nature Communications this week that the cells that give rise to the tumours do not have functional TSC2 and can stimulate hair follicle formation in some grafts. This harmatoma xenograft model may also allow for the further study of tissue organisation.