With approximately 42% of Americans rocking some sort of eye glasses, contact lens, or Lasix surgery, ophthalmological research has been on the rise over the past quarter decade. This summer was no different. Researchers at the Albert Einstein College of Medicine have found that there are several specific DNA repair enzymes and pathways that appear to be crucial for denucleation in embryonic mice lens fiber cells, which compose the structure of the ocular lens. The researchers studied certain chemical processes that are involved with taking apart the nucleus of a cell. The cells they studied were part of the eye’s ocular lens in embryonic mice
The primary goal of the research was to use these mice to then evaluate and understand the process of transparent lens formation, and determine which key genes, when mutated, lead to the destruction of the optic lens and the formation of cataracts. Cataracts can prevent clear vision and in certain instances be so severe that they cause blindness. According to the American Academy of Ophthalmology, cataracts affect 22 million Americans ages 40 and older. This research is part of an effort to present cataracts.
I was afforded the incredible opportunity by Yeshiva University to participate in the Summer Undergraduate Research Program at Albert Einstein College of Medicine. As part of this program, I was assigned to work in a specific lab geared toward my particular interests and field of expertise. I was paired up with Dr. Ales Cvekl in the department of Ophthalmology, Genetics, and Visual Sciences. As I made the dissections and ran tests, I was able to get a feel for what it means to be involved in a laboratory on a day-to-day basis and got a front row seat to this specific research.
The lens is a very important component of the eye as it refracts incoming light to be transmitted on the retina where an image can be processed and visualized. In order for the lens to work properly and efficiently, the lens fiber cells must be transparent. Subcellular organelles such as the nucleus reduce transparency and hinder the ability of the lens to do its job properly. Therefore, denucleation is a critical process that takes place during embryonic development in which the lens fiber cells remove the nucleus. If denucleation does not take place, clouding of the lens would occur, leading to the onset of cataracts. Age onset cataract formation is responsible for 48% of the total occurrences of blindness world-wide, affecting 18 million people. Understanding, and identifying some of the key biological pathways that when mutated lead to cataract formation is the first step in the attempt to circumvent cataract formation and the need for surgery.
As the denucleation process occurs, double stranded DNA breaks form and chromatin, content of the nucleus, degrades. Therefore previous research has indicated that in order to counteract this and prevent apoptosis, programmed cell death, which would produce optical irregularities and scattering of light, DNA repair enzymes were mobilized. The purpose of this experiment was to identify the functional DNA repair enzymes participating in the denucleation process.
In order to test this hypothesis, dissections were made to remove the lens of embryonic mice from three different stages of development: day 15.5 of development before denucleaution occurs, day 17.5 of development while denucleation is taking place, and after the mice were born post-denucleation. Genetic content of the lens were then analyzed at each stage to see whether DNA repair enzymes were activated during denucleation. Through comparison of these three different stages in mouse development, it was determined which genes were uprgeluated, or activated at an increased rate, and during which stages of development. Specifically, the research looked for genes that displayed an upregulation from day 15.5 to day 17.5 followed by a down regulation or no significant change from day 17.5 to newborn. This indicates that these genes were activated, most likely, specifically for the denucleation process.
After running the tests, it was concluded that Nbn, a DNA repair enzyme called nibrin that forms a complex with two other proteins: Rad 50 and Mre11a, to form the MRN complex is indeed upregulated during denucleation therefore proving the hypothesis that DNA repair enzymes are crucial for the formation of lens transparency and the prevention of cataract formation. Interestingly, it is known that Brca1 binds to Rad50, which in turn is bound to Mre11 and Nbn, meaning that Brca1 is yet another player in this specific DNA repair pathway. Upon analysis of the data to see if Brca1 also showed an activation during denucleation, research found that not only is it activated but that Brca1 displayed very similar patterns of mRNA expression at all stages of development compared to that of Nbn. This alludes to the possibility that not only does Brca1 work in concert with the MRN complex but that possibly Brca1 is also co-regulated with Nbn. This shows that not only are specific DNA repair enzymes needed during denucleation but also that specific pathways with many enzymes are crucial for denucleation to take place efficiently and correctly.
While still in its initial phases, Einstein’s findings will be quite useful for further research in cataract prevention and blindness.