The cytoskeletal network and cellular function in rod and cone photoreceptors are disrupted in the absence of NUDC expression

Abstract

Purpose : We have shown Nuclear Distribution Protein C (NUDC) has a critical role in the maintenance of rod photoreceptors by regulating outer segment (OS) disk size, likely through actin regulation. We propose that NUDC influences cytoskeletal elements such as microtubule structure and the trafficking of mitochondria or proteins destined for the OS. Here we expand our understanding of the role of NUDC in photoreceptors by testing the hypothesis that NUDC regulation of the cytoskeleton is critical both in rods and cones.

Methods : We generated a NudC floxed mouse and bred it with the rod-cell specific iCre75 or the cone-cell specific HRGP Cre recombinase mouse to produce NudC^+/- or NudC^-/- in rod or cone photoreceptors, respectively. Retinal function was analyzed using electroretinography (ERG) at P21 and P42, and retinas were isolated and examined by transmission electron microscopy (TEM), immunohistochemistry (IHC), and Western blotting (WB).

Results : ERG analysis uncovered low a- and b-wave amplitudes in P21 rod NudC^-/- (rNudC^-/- ) mice under scotopic conditions. IHC staining of retinal cryosections from rNudC^-/- 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. IHC and WB for GFAP also show an increase in gliosis in the rNudC^-/- retinas compared with rNudC^+/+. WB of rNudC^-/- retinal lysates show a decrease in rhodopsin, cofilin, and transducin, an increase in LIS1 and Rab11a while ARR1 levels were unchanged compared with rNudC^+/+. TEM taken from ultrathin sections of rNudC^-/- retina show disorganized disk formation and striking morphological changes in the IS. In mice lacking NUDC in cones (cNudC^-/-), the scotopic ERG response at P21 displays a normal a-wave and a diminished b-wave that is further reduced at 6 wks. The photopic ERG is decreased at P21 and is absent at P42.

Conclusions : NUDC is critical in rod photoreceptor OS disk formation and in localization of mitochondria and phototransduction proteins. Our data are consistent with the hypothesis that NUDC governs disk dimension through actin regulation, stressing the importance of this protein in the cytoskeleton of photoreceptors in development and during homeostasis. Similar to rods, we have found that NUDC is critical for proper cone cell function.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.