PKD1 and cyst: These data are also consistent with the idea that persistent cilia-based mitogenic signaling may support cell proliferation and cyst expansion in cells lacking Pkd1 or Pkd2. In fact, double-mutant mice lacking one of the polycystin genes and a gene essential for cilia formation, either ift20 or Kif3a, show a much less severe phenotype, in terms of cyst formation and cell proliferation, compared with single mutants (Ma et al, 2013).