The cytoskeletal network in photoreceptors is dependent upon NUDC expression

Abstract

Purpose : We have shown Nuclear distribution protein C (NUDC) has a critical role in the maintenance of post-mitotic rod photoreceptors by regulating outer segment (OS) disk diameter through interactions with actin. Here we test the hypothesis that NUDC is critical in microtubule cargo movement by examining the localization of rhodopsin and arrangement of mitochondria in the inner segment in the absence of NUDC mouse photoreceptors.

Methods : We have previously generated the NUDC floxed mouse and bred them with the rod-cell specific Cre recombinase (iCre75) mouse to produce NudC^+/- or NudC^-/- in rod photoreceptors. The retinas of the resulting mice were isolated and examined by electroretinography (ERG), transmission electron microscopy (TEM), immunohistochemistry (IHC), and quantitative PCR (qPCR) of mRNAs involved in fission and fusion of mitochondria.

Results : ERG analysis uncovered very low a- and b-wave amplitudes in 3wk-old NudC^-/- mice under scotopic conditions. IHC staining of retinal cryosections taken from NudC^-/- mice demonstrate disorganized microtubules in the inner segment (IS) of rod photoreceptor cells along with rhodopsin mislocalization in the IS, outer nuclear layer and synapse. Instead of long, fused mitochondria that align to the IS plasma membrane, TEM images of ultrathin NudC^-/- mouse retinal sections show mitochondria localized throughout the entire IS cytoplasm instead of adjacent to the plasma membrane as in wild type rods. Differences in expression of key genes critical for mitochondrial fission and fusion as measured by qPCR were statistically insignificant.

Conclusions : We have found that the protein NUDC is critical in rod photoreceptor OS disk formation and for mitochondrial localization in the IS. Our data are consistent with the hypothesis that NUDC governs disk dimension through actin regulation and mitochondrial localization through microtubule regulation, stressing the key importance of this protein in the cytoskeleton of photoreceptors in development and during homeostasis.

This is a 2021 ARVO Annual Meeting abstract.