NUDC is critical for regulation of photoreceptor cytoskeletal network

Abstract

Purpose : Nuclear distribution protein C (NUDC), primarily known for its role in cellular division and neuronal migration during development, regulates branching of actin and participates in the cytoplasmic dynein complex and molecular movement of cargo along microtubules. We have shown that NUDC has a critical role in the maintenance of post-mitotic rod photoreceptors by regulating disk formation in the outer segment (OS) through interactions with actin. Here we test the hypothesis that NUDC is critical in microtubule cargo movement by examining the arrangement of mitochondria as well as monitoring their fission and fusion 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 immunohistochemistry (IHC), transmission electron microscopy (TEM), and quantitative PCR (qPCR) of mRNAs involved in proper mitochondria arrangement as well as expression of genes involved in fission and fusion of mitochondria.

Results : IHC staining of retinal cryosections taken from NudC^-/- mice demonstrate microtubules that appear to be disorganized in the IS of rod photoreceptor cells. Instead of long, fused mitochondria that align to the IS plasma membrane, transmission electron microscopic images of ultrathin NudC^-/- mouse retinal sections show small mitochondria throughout the entire IS cytoplasm. To monitor whether the defect in localization of mitochondria is due to a lack of expression of key genes critical for fission and fusion of mitochondria, qPCR show statistically insignificant differences of genes involved in these processes, suggesting the defect is in mitochondrial trafficking along microtubules in the IS due to the lack of NUDC, not a lack of fission or fusion of these organelles.

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 2020 ARVO Annual Meeting abstract.