Figure 1.Have you ever wondered why nocturnal animals have such shiny eyes at night?
Researchers have now discovered the key element responsible for night vision. The secret lies in the DNA within the photoreceptor rod cells in the eye. The pattern of packaging of this DNA is very different to that of diurnal mammals. The DNA architecture turns the nuclei of the cells into light focussing lenses. There are millions of these cells in the eye of a nocturnal animal.
Fig.1 (above) In nocturnal to low light active mammals (e. g. the cat) the rod photoreceptors of the eye have nuclei with an inverted architecture, whereas the rods of diurnal mammals (e. g. the crab-eating macaque) have a conventional nuclear architecture. The inverted architecture improves nocturnal vision. (Credit: Leo Peichl, Max Planck Institute for Brain Research)
The conventional architecture of the DNA is present in the rod cells of all diurnal mammals including primates. However in nocturnal mammals, such as mice and cats, the DNA of the rod cells has a unique inverted architecture which grants that mammal with some amazing optical properties. Light that would usually be scattered in the eye of a diurnal mammal is instead focussed forward in the nocturnal animal. This allows the light to travel deep into the eye, by being passed from one cell to the next, to where it can be perceived.
This lead to the realization the structure of the nuclei rod cells might influence the behavioural patterns of nocturnal mammals during the day. This is because biologists typically think of DNA and its packaging into chromatin in terms of its effect on gene activity.
In diurnal animals the DNA associated with proteins now called chromatin in the eyes, is arranged in a way where the more condense heterochromatin at the periphery, and the less condense euchromatin at the interior. The researchers discovered that in nocturnal mammals the arrangement is the opposite. The euchromatin contains transcription factors that control the activity of genes. These are located at the periphery in nocturnal mammals.
What is more intriguing is that the researchers found out that this inverted arrangement of DNA was not present in mice at birth, but was developed over the first few weeks of life.
The birth of mice with conventional arrangement suggests that the conventional arrangement of DNA is strongly conserved among mammals today. However, the occurrence the inverted arrangement is a process of evolution that is selected for, in nocturnal animals. This sheds light upon how short a time interval is required for evolution to create new properties in an organism in comparison to the more commonly studied traits inherited through evolution over millions of years.
Source:
http://www.sciencedaily.com/releases/2009/04/090416125159.htm
