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Seeing through the Dark

Suma Satish-Chandra, MS biology '09, is looking at evolution through a different set of eyes. Under the guidance of Professor David Carlini, she has spent the past two years investigating the nature of eyesight in tiny freshwater-dwelling crustaceans called amphipods. Like many members of the animal kingdom, these shrimp-like creatures use opsin, a protein found within the retina's photoreceptor cells, to help them convert photons of light into electrical signals that their brains interpret as images.

Satish-Chandra is examining an amphipod species that resides in both surface and underground water throughout the eastern United States. The stark distinction between these two environments causes differences in the evolution of the entirely light-dependent opsin protein. By studying the opsin gene sequences and expression in these organisms, Satish-Chandra has observed the development of genetic differences between the two populations and generated a better understanding of the evolutionary processes that may ultimately lead them to evolve into two unique species.  

To observe these genetic differences in the two populations, Satish-Chandra first isolated the opsin DNA sequence from the entirety of the amphipod's genome by designing DNA primers—small sequences of RNA that complement a region upstream and downstream of the opsin gene. Satish-Chandra then used a technique called polymerase chain reaction (PCR) to isolate and amplify the sequences, leaving Satish-Chandra with strands of DNA that contain only the opsin gene.  

Using American University's DNA sequencer, Satish-Chandra then read out the sequences for members of each population and searched for distinct differences between them. Because the population within cave systems no longer needs its opsin protein, Satish-Chandra says that individuals from this population that accumulate detrimental opsin gene mutations are more likely to pass on these mutations than their surface cousins, since detrimental opsin mutations would endanger their survival. Therefore, Satish-Chandra explains, it would make more sense for the surface population's opsin sequence to be more constrained over evolutionary time, and therefore far more functional, due to the population's life in the daylight.  

Satish-Chandra completed her degree this December and is planning to return to her native India. There, she aims to work in the fast-paced world of Indian biotechnology, hoping to work in her home country as a research associate at one of India's biotech or research institutes.  

Adapted from "Seeing through the Dark: Suma Satish-Chandra Traces Evolution of the Opsin Gene," by Chelsea Babcock, Catalyst, Fall 2009.