One of the most notable features of the vertebrate eye is its retina on the inside of the eye. Surprisingly, the sensitive parts of the photoreceptor cells are on the back of the retina. Therefore, the light has to travel through living nerve tissue before it can be perceived. A special DNA organization could help improve vision in nocturnal mammals. Researchers at the Max Planck Institute for Molecular Cell Biology and Genetics in Dresden are now showing that the optical quality of the retina in mice increases in the first month after birth. This leads to an improved visual sensitivity in difficult lighting conditions. This is caused by the compact organization of the genetic material in the cell nucleus of rod photoreceptor cells.
Seeing at night is one of the most difficult and important tasks in evolution. This explains the complexity of the eye and its light-sensitive retina.[fewer]
Credit: © Ernie Janes / Alamy Stock Photo
The retina is perhaps the most amazing part of the vertebrate eye. This light-sensitive fabric layer lines the back of the eyeball and serves as a projection surface for the images projected by the lens. The retina has a thickness of 130 to 500 micrometers, which corresponds to the thickness of several sheets of paper, and consists of five layers of dense nerve tissue. Since the sensitive parts of the photoreceptor cells are on the back of the retina, the light has to travel through this dense nerve tissue to reach the photoreceptors. Researchers have long suspected that a certain compact arrangement of DNA in the nucleus of the rod photoreceptors could improve vision in nocturnal animals, but it has remained unclear
Scientists led by research group leader Moritz Kreysing at the Max Planck Institute for Molecular Cell Biology and Genetics wanted to find out together with colleagues from the TU Dresden and the bio center of the Ludwig Maximilians University in Munich whether and why cells of the retinal nerve cells are optically special and what effects this has on the transparency of the retina. In this context, transparency means that each rod cell scatters less light and is therefore more transparent.
DNA rearrangement improves transparency
The researchers particularly focused on the importance of DNA densification in the rod photoreceptor cells and whether changes in the optical properties of the retina are strong enough to improve mouse vision under difficult lighting conditions. Kaushikaram Subramanian, the lead author of the study, explains: “When examining mice, we found that the optical quality of the retina increased during the first month after birth. There is a twofold improvement in retinal transparency caused by the compact rearrangement of the genetic material in the cell nucleus. With behavioral tests under moonlight conditions, we were also able to show that mice with this DNA adjustment could see better under poor light conditions than mice that lacked such an arrangement.
Research not only reveals the function of this unusual DNA organization in the retina. Furthermore, the work shows that image clarity is not only a question of the image projection lens, but also depends on the optical quality of the retina. Moritz Kreysing, who supervised the study and is also a member of the Center for Systems Biology Dresden, summarizes: “Our study further indicates that genetics methods could be used to change the optical properties of cells and tissues. It would be exciting to see whether genetics can be used to improve the transparency of cells and tissues, which would greatly benefit biological microscopy of living tissues. ”
Contacts and sources:
Max Planck Institute for Molecular Cell Biology and Genetics
Publication: Kaushikaram Subramanian, Martin Weigert, Oliver Borsch, Heike Petzold, Alfonso Garcia, Eugene Myers, Marius Ader, Irina Solovei, Moritz Kreysing:
Rod nuclear architecture determines contrast transmission of the retina and behavioral sensitivity in mice eLife, December 11, 2019 DOI