Abstract
Purpose: :
Retinal Degeneration Slow (RDS) is a structural protein necessary for outer segment (OS) morphogenesis. Loss of RDS in the cone-dominant retina of the Nrl-/- (neural retinal leucine zipper) mouse produces morphologically abnormal cones with OSs that do not associate with the IPM but are still capable of phototransduction. In this study we characterize the developmental associations between cone OS and IPM in normal and RDS-deficient retinas.
Methods: :
Frozen and paraffin embedded sections of eyecups from WT, Nrl-/-, Nrl-/-/Rds+/-, and Nrl-/-/Rds-/- mice were collected at post-natal (P) day 1, 5, 8, 10, 12, 15, 21, and 30. Double-label immunohistochemistry for S-opsin and peanut agglutinin (PNA) was used to visualize cone OSs and the IPM, respectively, and retinal structure and OS/matrix interactions were examined by spinning disk confocal microscopy.
Results: :
No differences in timecourse of opsin or IPM expression were detected in any genotype. Distinct PNA labeling appeared in the outer retina by P5, slightly before S-opsin labeling which appeared between P5 and P8. At early time points (P8-P10), PNA was detected only around inner segments even if OSs were present. In WT and Nrl-/- retina, PNA staining began to associate with OSs labeled for S-Opsin between P12 and P15, but no association was detected in Nrl-/-/Rds+/- or Nrl-/-/Rds-/- retina. In Nrl-/- mice of any Rds background, rosettes appeared by P10, but were absent at earlier ages.
Conclusions: :
Secretion of the cone IPM appears to start around P5 and is associated initially with the inner segment through P10, even though OS formation is ongoing. Rosette formation begins around P10 and coincides with the rapid development of OSs. The observation that interactions between cone OSs and the IPM, as visualized by PNA labeling, develop after OS development is initiated (and never develop in Nrl-/-/Rds-/- retina) suggests that the lack of association between RDS-deficient cones and the IPM results from the structural abnormalities of the OS.
Keywords: photoreceptors • extracellular matrix • development