Abstract
As part of the International Mouse Phenotyping Consortium (IMPC) programme, the MRC Harwell is conducting a large eye morphology phenotyping screen on genetically modified mice compared to the baseline phenotype observed in the background strain of C57BL/6NTac. The C57BL/6NTac strain is known to carry a spontaneous mutation in the Crb1 gene that causes retinal degeneration characterized by the presence of white spots (flecks) in the fundus. These flecks potentially represent a confounding factor, masking similar retinal phenotype abnormalities that may be detected in mutants. Therefore we investigated the frequency, position and extent of the flecks in a large population of C57BL/6NTac mice to provide the basis for evaluating the presence of flecks in mutant mice with the same genetic background. We found that in our facility males were more severely affected than females and that in both males and females the most common localisation of the flecks was in the inferior hemicycle of the fundus.
Highlights
Retinal degeneration in mice occurs in many forms, many of which can be attributed to mutations in specific genes
The observed phenotype is considered a possible confounding factor that could mask a phenotype with a similar appearance but a different causative gene mutation (Figure 1). This is of particular importance considering that the C57BL/6N line is a widely used commercial line and is the background strain used for the generation of gene-targeted mice in several mouse mutagenesis/phenotyping programmes, including the International Knockout Mouse Consortium (IKMC) and the International Mouse Phenotyping Consortium (IMPC)
Further categorising the flecks according to our scoring system, we observed that the males were still the most affected in the score classes ranging from I1 to I3 (Figure 3), with 1 superior (S1) 0 inferior
Summary
Retinal degeneration in mice occurs in many forms, many of which can be attributed to mutations in specific genes. It has been previously reported that the C57BL/6N strain, derived from the unaffected C57BL/6J strain, often presents typical retinal white spots (flecks) caused by the Crb1/rd[8] mutation[4]. These have been described as dysplastic lesions affecting the retinal region between the inner and the outer nuclear layer and are mainly localised in the inferior part of the retina[5,6]. This is of particular importance considering that the C57BL/6N line is a widely used commercial line and is the background strain used for the generation of gene-targeted mice in several mouse mutagenesis/phenotyping programmes, including the International Knockout Mouse Consortium (IKMC) and the International Mouse Phenotyping Consortium (IMPC)
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