a, a′ Addition of 10 nM rapamycin (Rapa) to control zebrafish has no effect on morphology at 5 dpf. Asterisk indicates the swim bladder (not visible in morphant embryos). b– e′ bbs6, bbs8, nphp2 and nphp6 all show a dramatic reduction in kidney oedema (outlined) following the addition of Rapa. Other morphological phenotypes are unaffected by the treatment. f, f′ mks1 morphants all die by 5 dpf without Rapa, but 75% survive and show reduced kidney swelling after the addition of Rapa. g, g′ ift80 morphant kidney phenotype is also reversed by Rapa. Note that the pericardial oedema and curved body axis are unaffected by the drug. h Roscovitine (Rosc) also reduces the size of the kidney swelling but to a much lesser extent than Rapa. It also appears to ameliorate some of the cardiac oedema. i Graph showing the lateral surface area of the kidney oedema with and without Rapa for all ten genes knocked down. In all cases, the addition of Rapa reduced the kidney to levels similar to that of the controls. j Addition of a range of Rosc concentrations to ift80 morphants shows dosage-dependency, but even at high doses it is unable to reduce kidney swelling to the extent of Rapa (MO morpholino oligonucleotide). k Fluorescent image of an embryo 3 h after injection of rhodamine dextran into the heart. Fluorescence disperses throughout the circulation. k′ The same embryo 24 h after injection shows the complete absence of fluorescence as it has all been evacuated by the kidney. l Fluorescent dextran perfuses systemically throughout the ift80 morphant to the same extent as controls 3 h after injection. l′ The same embryo 24 h after injection still has residual fluorescence in the circulation. m, m′ Close-up of the heart of a control zebrafish showing the elimination of fluorescence after 24 h. n, n′ Persistence of fluorescence after 24 h in ift80 morphants, particularly in the pronephros (arrowhead). o, o′ treatment with Rapa reduces the residual fluorescence in morphants, particularly in the heart, but some still persists in the pronephros (arrowhead). p, p′ treatment with Rosc also partially rescues the filtering defect but less so than Rapa (arrowhead). q Graph quantifying the percentage of original fluorescence remaining in the kidney 24 h after injection. Addition of drugs has no effect on control embryos. Fluorescence is reduced to a similar level as that in untreated ift80 and bbs4 morphants, but both drugs have a slightly more marked effect on bbs4 than ift80 morphants. This graph also shows that Rapa is more effective than Rosc in this system. In all graphs, error bars represent the standard error of the mean (n ≥ 10 embryos in all cases). Bars (a–h) 1 mm, (k–l′) 1 mm, (m–p′) 100 μm