PDE6B and retinitis pigmentosa 1: Upregulation of the endothelin pathway has been found in a number of other mutant retinas causing RP, including those of rd10 mice, where the phosphodiesterase 6b (Pde6b) is mutated [18], endothelin signal antagonists are adequate to ameliorate the degenerating phenotype [18, 54], and diabetic model db/db mice carrying a mutation in the leptin receptor gene [55].