However, it is an open question whether the α-transducin investigated refers to the non-visual α-transducin Gnaz and/or the visual α-transducins Gnat1 and/or Gnat2. The aim of the present study was to investigate (1) as to what extent expression of Gnaz, Gnat1 and/or Gnat2 is under daily regulation in retina, photoreceptors and photoreceptor-related pinealocytes, (2) depends on a circadian clock, (3) is regulated by the neurohormones melatonin and dopamine and (4) is disturbed in diabetic retinopathy. The gene discussed is GNAT1; the disease is diabetic retinopathy.