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01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
01:11Genetic Lingo
Overview
01:19X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
01:19X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
01:24Color Vision
Color perception begins in the retina, the light-sensitive layer at the back of the eye. Two main theories explain how colors are seen: the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, suggests that color vision is based on three types of cone receptors in the retina. These cones are sensitive to different but overlapping ranges of wavelengths corresponding to red, blue, and green.
02:32Position-effect Variegation
In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
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Variations in opsin coding sequences cause x-linked cone dysfunction syndrome with myopia and dichromacy.
Michelle McClements1, Wayne I L Davies, Michel Michaelides
1University College London Institute of Ophthalmology, London, United Kingdom.
Investigative Ophthalmology & Visual Science
|January 17, 2013
Summary
Variant L opsin haplotypes are linked to Bornholm Eye Disease (BED), a condition causing dichromacy and myopia. These genetic variations affect pigment stability and may explain the disease
Area of Science:
- Genetics
- Ophthalmology
- Molecular Biology
Background:
- Bornholm Eye Disease (BED) is a cone dysfunction syndrome characterized by dichromacy and myopia.
- The genetic basis of BED, particularly the role of opsin genes, requires further elucidation.
Purpose of the Study:
- To investigate the association between variant L opsin haplotypes and Bornholm Eye Disease (BED).
- To analyze the functional impact of identified opsin variants on pigment formation and cellular localization.
Main Methods:
- Opsin gene analysis in BED families using cloning, sequencing, and quantitative PCR.
- In vitro expression studies of normal and variant opsins to assess pigment function and trafficking.
Main Results:
- Rare exon 3 L opsin haplotypes were identified in most BED families.
- Variant opsins formed functional pigments but exhibited reduced stability compared to wild-type.
- Defective splicing of the variant opsin transcript was also observed.
Conclusions:
- Variant L opsin haplotypes are implicated as the underlying cause of BED.
- Reduced opsin stability and/or defective splicing are potential disease mechanisms.
- These genetic factors may explain the observed dichromacy, cone dystrophy, and myopia in BED.