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Guoxin Ying, Jeanne M. Frederick, Wolfgang Baehr; Germline deletion of both CETN2 and CETN3 destabilizes the distal connecting cilium of mouse photoreceptors. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3977.
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Centrins (CETN1-4) are ubiquitous, conserved, EF-hand family Ca2+-binding proteins associated with the centrosome, basal body and transition zone. Deletion of either CETN1 or CETN2 in mouse caused male infertility and dysosmia, respectively, without affecting retina development or photoreceptor function. We now generated CETN3 and CETN2/CETN3 dKO mice to explore its effect on photoreceptors
Generation of CETN3 single and CETN2/CETN3 dKO mice using gene traps (GT). Cetn3-/- mice were generated by removal of GT and deletion of exon 3 whereas Cetn2-/- mice were generated by deletion of exons 2 and 3. dKO mice were generated by crossbreeding. Mutant mice were phenotyped by ERG, confocal and electron microscopy.
Centrins associate with microtubules of the centriolar lumen and connecting cilium axoneme. While deletion of Cetn3 did not affect photoreceptor function, simultaneous deletion of Cetn2 and Cetn3 resulted in attenuated scotopic and photopic ERG responses at three months of age, with nearly complete retina degeneration at one year. CETN2/CETN3 dKO mice showed more severe syndromic ciliopathy (olfactory and ependymal cilia defects) than Cetn2-/- mice. Double knockout ciliogenesis (docking of basal body, extension of axoneme and disc morphogenesis) was normal, but photoreceptor axoneme length was reduced as early as postnatal day 22 (P22) as determined from reduced RP1 and acetylated α-tubulin decoration at the CC. Ultrastructural analysis of dKO photoreceptors revealed shortened CC, expanded distally, with vertically misaligned outer segment (OS) discs and membrane whorls. Absence of CETN2/3 abrogated the association of SPATA7 with the CC; SPATA7 is a known stabilizer of the distal CC whose defects are associated with nonsyndromic LCA.
These observations suggest that CETN2 and CETN3 cooperate redundantly in stabilizing the CC/axoneme structure of rods and cones. Absence of CETN2 and CETN3 eliminated SPATA7 association with the distal CC, weakening the nine doublet microtubule structure and impairing disc assembly and alignment.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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