Figure 4. Triallelic loss of Mkks and/or the Cep290-DSD domain ameliorate cilia phenotypes in photoreceptors.

(A) Cross sections through the P18 retina in different combinations of Cep290^rd16 and Mkks^ko alleles, as indicated. Note the short, abnormal OSs in Cep290^rd16/rd16 or Mkks^ko/ko genotypes and the more normal OS in the triallelic Cep290^rd16/+;Mkks^ko/ko genotype. Here, the Cep290^rd16/rd16;Mkks^ko/ko genotype looks similar to Cep290^rd16/rd16. The white arrows indicate comparison between 2 similar genotypes that are improved by combining alleles of Cep290 and Mkks. Original magnification, ×40. (B) Quantitation of outer nuclear layer thickness at P18 in the genotypes indicated. Higher variability is noted in double-homozygous mutants (see error bars on Cep290^rd16/rd16 versus Cep290^rd16/rd16;Mkks^ko/ko). Error bars are SD; n = 6 (WT), n = 4 (Cep290^rd16/+;Mkks^ko/ko), n = 3 (Mkks^ko/ko), n = 14 (Cep290^rd16/rd16;Mkks^ko/ko), n = 8 (Cep290^rd16/rd16). (C) Scotopic ERG b-wave amplitudes in the indicated mouse genotypes (at P20). Removing one WT Mkks allele on a Cep290^rd16/rd16 background results in improved responses, as does adding one Cep290^rd16 allele on a Mkks^ko/ko background. Note that single homozygous or double-homozygous genotypes have essentially no ERG b-wave response. Error bars are SD; n = 3 (WT), n = 3 (Cep290^rd16/rd16), n = 6 (Cep290^rd16/rd16;Mkks^ko/+), n = 4 (Mkks^ko/ko), n = 3 (Cep290^rd16/+;Mkks^ko/ko), and n = 3 (Cep290^rd16/rd16;Mkks^ko/ko). (D) Longitudinal EM sections through the OS, connecting cilia, and inner segments in P14 retina show that OS morphology is disrupted in the indicated mutant genotypes. Original magnification, ×3,000. (E) Higher-magnification images (original magnification, ×30,000) of OSs in P14 retina confirm improved OS morphology in Cep290^rd16/+;Mkks^ko/ko and Cep290^rd16/rd16;Mkks^ko/+ triallelic genotypes. OSs of triallelic mice form concentric stacks of discs (parallel orange lines), more similar to WT. The white arrows indicate comparison between 2 similar genotypes that are improved by combining alleles of Cep290 and Mkks. RPE, retinal pigment epithelium; CC, connecting cilia; IS, inner segment; ONL, outer nuclear layer; OPL, outer plexiform layer; INL, inner nuclear layer; ONH, optic nerve head.