Table 1.
Comparison of photoreceptor phenotypes in zebrafish IFT mutants between 60 and 96 hpf and correlation with other ciliary defects.
| Outer segment (OS) morphogenesis | Photoreceptor-related function | Other affected tissues and functions | |||
|---|---|---|---|---|---|
| 60 hpf | 72 hpf | 96 hpf | |||
| Wild type | Observable OS in ventral patch | More OS observed | More OS appear | ||
| OS ≈ 2 μm in length | No change in length | Tiering between rods and cones becoming evident | |||
| Loose organization of disk membranes. | Disk membranes highly ordered | OS length increased to 4 μm | |||
| Rhodopsin trafficking to OS | Rod and cone opsins seen in OS | Complete OS localization for rod and cone opsins | |||
| ift57-/- | OS phenotype similar to wild type | 88% fewer OS than wild type | 90% fewer OS than wild type | Not essential for OS formation and disk membrane organization | Cilia formation in C. elegans (che-13) (Haycraft et al., 2003) |
| Mild mislocalization of rhodopsin | Length similar to wild type at ≈ 2 μm | Length increases slightly to ≈ 2.5 μm | Required for OS growth and photoreceptor survival | Kidney and nodal cilia in zebrafish and mice (Houde et al., 2006, Kramer-Zucker, Olale, Haycraft, Yoder, Schier & Drummond, 2005) | |
| Disk membranes organizes | More rod and cone opsins mislocalized to inner segment | Auditory and olfactory cilia formation in zebrafish (Tsujikawa & Malicki, 2004) | |||
| Rod and cone opsins seen in OS but also mislocalization | Photoreceptors begin apoptosis | ||||
| ift88-/- | No OS observed | No OS observed | No OS observed | Essential for primitive cilium extension and OS formation | Flagella formation in Chlamydomonas and C. elegans (Haycraft et al., 2003, Pazour et al., 2000) |
| Disorganized membrane material observed in apical inner segment | Increase in number of disorganized membrane arrays | Complete mislocalization of rod and cone opsins | Not essential for basal body localization | Kidney and nodal cilia in zebrafish and mice (Kramer-Zucker et al., 2005, Yoder, Tousson, Millican, Wu, Bugg, Schafer & Balkovetz, 2002) | |
| Strong mislocalization of rhodopsin | Complete mislocalization of rod and cone opsins | Photoreceptors begin apoptosis | Auditory and olfactory cilia formation in zebrafish (Tsujikawa & Malicki, 2004) | ||
| ift172-/- | No OS observed | No OS observed | No OS observed | Essential for primitive cilium extension and OS formation | Anterograde and retrograde transport in Tetrahymena and Chlamydomonas flagella (Pedersen, Miller, Geimer, Leitch, Rosenbaum & Cole, 2005, Tsao & Gorovsky, 2008) |
| Disorganized membrane material observed in apical inner segment | Increase in number of disorganized membrane arrays | Complete mislocalization of rod and cone opsins | May play role in positioning centrioles for basal body localization | Nodal cilia formation in mice (Huangfu et al., 2003) | |
| Strong mislocalization of rhodopsin | Complete mislocalization of rod and cone opsins | Photoreceptors begin apoptosis | |||
| Some mislocalization of centrin observed | |||||