Finally, the identification of genes encoding ion channels whose expression varied with age such as Pkd2 (Polycystic kidney disease 2) and Clic (Chloride intracellular channel), together with genes involved in neural signalling and development or cytoskeleton organisation such as Nlg1 (Neuroligin 1) or Actn (α actinin; Supplementary Data 1), may indicate that TFCs-CpCs could be excitable and/or respond to ion fluxes, much as neurons or muscle cells do42,43. The gene discussed is PKD2; the disease is polycystic kidney disease 2.