TCTN2 and nephronophthisis: Further, we examined several transition zone proteins in the cilia, including NPHP1, which is mutated in nephronophthisis (OMIM 607100), TCTN2, MKS1, and MKS3, using immunostaining and TEM; we found that NPHP1, TCTN2, and MKS1 were markedly decreased in NDUFAF2–/– RPE cells, indicating that NDUFAF2 regulates the establishment of the transition zone (Figure 1, J–O, and Supplemental Figure 3, I–L).