The Emergence of Rod-Cone Cellular Interaction

Area of Science:

• Evolutionary biology
• Molecular biology
• Neuroscience

Background:

• Rod-derived cone viability factor (RdCVF) is a thioredoxin-like protein produced by the NXNL1 gene in mammalian rod photoreceptors.
• RdCVF prevents secondary cone degeneration in models of retinal disease.
• It functions by binding to a basigin-1/GLUT1 complex on cone cells, enhancing glucose uptake.

Purpose of the Study:

• To investigate the evolutionary origins and development of RdCVF signaling.
• To understand the ancient roles and diversification of RdCVF in different species.

Main Methods:

• Comparative analysis of gene sequences and protein functions across diverse species.
• Investigation of alternative splicing events in RdCVF and its receptor BSG1.
• Tracing the presence and function of RdCVF signaling from primitive organisms to mammals.

Main Results:

• RdCVF signaling predates the eye, with initial roles observed in hydra.
• The first RdCVF/BSG1 signaling interaction was identified in scallops, involving ciliated photoreceptors.
• Fully operational RdCVF metabolic signaling between rods and cones is present in lampreys.
• In mice, BSG1 production is regulated by alternative splicing, and the signaling extends to the brain via NXNL2.

Conclusions:

• RdCVF signaling evolved through alternative splicing events, starting with basic signaling and progressing to complex metabolic support.
• The RdCVF pathway is ancient and conserved, playing vital roles in photoreceptor health and extending to neural tissues.