Cross-species molecular mapping of the photoreceptor sensory cilium and periciliary structures identifies conserved and species-specific architectural features

Key results

1. 01

   ShownRod-cone differences in the microtubule-based ciliary core are conserved in dog, macaque and human: cones have shorter connecting cilia (CC), longer daughter centrioles (DC) and a more pronounced axonemal bulge than rods.

   CEP290-based CC significantly shorter in NHP cones than rods, as in canine, confirmed with SPATA7 and glutamylation; cone DC longer than rod DC in both (three canine, two NHP eyes; Welch's ANOVA, Dunnett's T3); bulge judged qualitatively in axial views. Both human donors kept cone CC < rod CC and cone DC > rod DC despite significant inter-donor differences. · PSC architecture shows shared rod–cone patterns…; Human PSC architecture aligns with primate…; Figure legends

2. 02

   ShownPrimate ciliary cores differ in scale from canine ones: NHP CCs are shorter with stronger distal widening and a larger bulge, NHP cones carry exceptionally long DCs, human data track the primate pattern, and DC length also separates cone subtypes.

   CC significantly shorter in NHP than canine for rods and cones; basal CC axoneme width similar across canine and NHP rods and cones (near the ~200 nm reported in mouse); NHP cone DCs approximately twice other groups, human cones longer still in pooled donor data (descriptive); L/M-cone DCs longer than S-cone DCs in all three species, with no CC difference. · PSC architecture shows shared rod–cone patterns…; Human PSC architecture aligns with primate…; Figure legends

3. 03

   ShownThe USH2 protein Whirlin marks a periciliary membrane confined to the inner segment (IS)-facing side of the CC in canine rods, but encircling the CC in NHP rods, human rods, and canine, NHP and human cones.

   Seen in lateral views, 3D reconstructions, NHS-ester counterstain and axial line profiles; many Whirlin puncta resolved into paired pillar-like elements around the CC; canine cones uniquely had an extra ectopic Whirlin cluster along the IS plasma membrane, present in all canine replicates though variable between cells. · Periciliary structures exhibit rod-cone…; Human periciliary structures are broadly…; Discussion

4. 04

   SuggestedPCDH15 (USH1F) and beta-actin co-patterns indicate calyceal processes in NHP and human rods and in canine, NHP and human cones (more robust in human cones than rods), whereas canine rods seem to lack them or have only minimal versions.

   Canine rods: PCDH15 mostly limited to the IS/OS junction, with discontinuous IS actin lacking PCDH15 association. NHP rods and canine and NHP cones: PCDH15 also extended axially along the basal outer segment (OS), associated with actin filaments reaching from the IS (described as continuous in NHP rods). Human donors matched this, with weaker axial PCDH15 in replicate 1. · Periciliary structures exhibit rod-cone…; Human periciliary structures are broadly…; Discussion

5. 05

   SuggestedAccessory inner segment (aIS)-like extensions containing mitochondria appeared in one of two human donors, in both rods and cones (contrary to the prior rod-only description), and were absent from canine and NHP photoreceptors.

   Donor replicate 2 (84-year-old female): some rods and cones had IS-derived extensions beside the OS holding cytochrome c-positive mitochondria, bounded by an elongated PCDH15-positive junction; tubulin was uneven, resembling the general IS network rather than a dedicated scaffold. Replicate 1 (83-year-old male), canine and NHP cells lacked these. · Human periciliary structures are broadly…; Discussion; Human donor eye tissue; Figure legends