Abstract
In the mammalian retina, rods and a specialised rod-driven signalling pathway mediate visual responses under scotopic (dim light) conditions. As rods primarily signal to rod bipolar cells (RBCs) under scoptic conditions, disorders that affect rod or RBC function are often associated with impaired night vision. To identify novel genes expressed by RBCs and, therefore, likely to be involved in night vision, we took advantage of the adult Bhlhe23−/− mouse retina (that lacks RBCs) to derive the RBC transcriptome. We found that genes expressed by adult RBCs are mainly involved in synaptic structure and signalling, whereas genes that influence RBC development are also involved in the cell cycle and transcription/translation. By comparing our data with other published retinal and bipolar cell transcriptomes (where we identify RBCs by the presence of Prkca and/or Pcp2 transcripts), we have derived a consensus for the adult RBC transcriptome. These findings ought to facilitate further research into physiological mechanisms underlying mammalian night vision as well as proposing candidate genes for patients with inherited causes of night blindness.
Highlights
In the mammalian retina, rods and a specialised rod-driven signalling pathway mediate visual responses under scotopic conditions
In the Schubert-Bornschein type of congenital stationary night blindness (CSNB), the a-wave is normal but b-wave amplitudes are reduced. This type of CSNB is further subclassified into complete and incomplete forms: cCSNB is linked to genes expressed post-synaptically in rod and cone ON-bipolar dendrites (NYX, TRPM1, GRM6, LRIT3, GPR179) which affect ON-bipolar signalling, whereas icCSNB is linked to genes expressed pre-synaptically in photoreceptors (CACNA1F, CABP4, CACNA2D4) which affect ON- and OFF-bipolar signalling
Since scotopic vision is mainly dependent on rod and rod bipolar cells (RBCs) function, and defects in rod or RBC function or survival result in night blindness in animal models, it is likely that some of the genes we have identified in the developing and adult Bhlhe23−/− retina will be implicated in patients with electronegative scotopic ERGs from inherited causes of night blindness
Summary
Rods and a specialised rod-driven signalling pathway mediate visual responses under scotopic (dim light) conditions. RBCs are nearly absent from the adult retina of Prdm8eGFP/eGFP mice, as well as cone type 2 OFF-bipolar cells, resulting in a thinner INL12 In this model, scotopic and photopic b-wave amplitudes are reduced in ERG recordings, while the a-waves are preserved[12]. The Bhlhe23−/− and Prdm8eGFP/eGFP mouse models show that genetically-determined cellular defects involving RBCs cause an ERG phenotype resembling CSNB11,12 It is, possible that mutations in other RBC genes that affect RBC function or survival will result in night blindness and that further subclassifications of this disorder might be needed in future to better reflect the different possible pathogenetic mechanisms that can lead to night blindness
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