Disrupting the ciliary gradient of active Arl3 affects rod photoreceptor nuclear migration

Abstract

The small GTPase Arl3 is important for the enrichment of lipidated proteins to primary cilia, including the outer segment of photoreceptors. Human mutations in the small GTPase Arl3 cause both autosomal recessive and dominant inherited retinal dystrophies. We discovered that dominant mutations result in increased active G-protein—Arl3-D67V has constitutive activity and Arl3-Y90C is fast cycling—and their expression in mouse rods resulted in a displaced nuclear phenotype due to an aberrant Arl3-GTP gradient. Using multiple strategies, we go on to show that removing or restoring the Arl3-GTP gradient within the cilium is sufficient to rescue the nuclear migration defect. Together, our results reveal that an Arl3 ciliary gradient is involved in proper positioning of photoreceptor nuclei during retinal development.

Mechanisms underlying morphological and functional changes of cilia in fibroblasts derived from patients bearing ARL3T31A and ARL3T31A/C118F mutations

“…As shown in previous study, ARL3 D67V , ARL3 Q71L , and ARL3 Y90C variants had rod nuclei mislocalized to the inner nuclear layer during retinal development, 10 while ARL3 T31N was not. Consistent with the clinical findings, our study reveals distinct ciliary phenotypes in fibroblasts carrying ARL3 T31A/C118F and ARL3 T31A mutations.…”

“…3,5,[7][8][9] Suppression ARL3 expression has been demonstrated to result in deficiencies in cilia trafficking, 4 mutations in ARL3 can lead to defective cilia morphology, particularly in the OS of photoreceptors, 9 and dominant ARL3 mutants disrupting Arl3 activity in rods could lead to a nuclear migration phenotype. 10 Additionally, animals with ARL3 conditional knockout are unable to develop the CC and OS of photoreceptors, leading to rapid deterioration of optic cone and rod cells. 11,12 Nowadays, variations in the ARL3 gene have also been implicated in RP, 13,14 BBS, 15 and other retinal cilia disorders.…”

“…It belongs to the ARF (ADF) family, which plays a crucial role in cilia development, axoneme formation, and regulation of ciliary transport 3,5,7–9 . Suppression ARL3 expression has been demonstrated to result in deficiencies in cilia trafficking, 4 mutations in ARL3 can lead to defective cilia morphology, particularly in the OS of photoreceptors, 9 and dominant ARL3 mutants disrupting Arl3 activity in rods could lead to a nuclear migration phenotype 10 . Additionally, animals with ARL3 conditional knockout are unable to develop the CC and OS of photoreceptors, leading to rapid deterioration of optic cone and rod cells 11,12 .…”

Progenitor division and cell autonomous neurosecretion are required for rod photoreceptor sublaminar positioning

“…However, these migration defects were characterized by mislocalized rods in the INL. More recently Mattar et al ( 44 ) and Travis et al ( 45 ) identified factors that implicate the nuclear lamina and primary cilia as regulators of rod soma positioning within the ONL, respectively. While P0 electroporation results in a uniform distribution of rods within the ONL, overexpression of Casz1 or Arl3 mutants led to basally biased rods in the ONL.…”

Mapping protein distribution in the canine photoreceptor sensory cilium and calyceal processes by ultrastructure expansion microscopy

“…In studies of the primary cilium, ARL13B has frequently been employed as a marker for the ciliary membrane [48,49]. Since mutations in ARL13B gene have been associated with Joubert syndrome, a systemic ciliopathy accompanied by retinal dystrophy, the localization of ARL13B in photoreceptors has been discussed in various studies, with variable conclusions [50][51][52][53]. Although several recent reports using mouse retina have claimed that endogenous ARL13B localizes to the photoreceptor OS [54,55], we found specific localization of ARL13B to the ciliary rootlet in U-ExM-processed canine photoreceptors (Figure 8F).…”