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.