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Drosophila Gastrulation

Added on: 15-June, 2023

By: Aadya Nageswaran

It is one thing to observe Drosophila embryos under a microscope (they look like grains of rice with two appendages), but it is quite another, more mind-blowing experience, to watch that same tiny bundle of cells under a foldscope, and capture a time lapse of its growth. That is precisely what I did in the fly lab at Ashoka University during the summer break this year. I had volunteered to be a teaching assistant for the Life Science module of the Lodha Genius programme.

One of our experimental sessions was to observe aspects of embryonic development using a foldscope with Mitali Patil, a PhD student at NCBS-TIFR. Mitali has worked with foldscopes extensively in her life, and also with high school children who, being a part of the program, were as fascinated as I was by both the use of the foldscope and the results it could generate. There were, of course, certain crucial steps we had to perform before we could get to the exciting part; we had to bleach the embryos so that their chorion or outer membrane could be removed. This was needed in order to see through the embryo and observe growth more clearly. The bleached embryos were placed on slides with coverslips on top, and we were ready to take a time lapse. Mitali helped set up the slide in the foldscope and focus on one embryo. She also suggested using a dark field, which is achieved by letting light in at an angle, and this is the reason the video came out with such bright colours.

There were two dead-giveaways of the possible stage that the embryo under observation was at: One, there was little movement at the beginning in the body of the embryo but constant flow at the edges, and two, there were pole cells at the posterior end of the embryo. To anyone well-versed in the field, this is indicative of the first few hours of Drosophila embryogenesis. Naturally, I eagerly waited by my foldscope. Although everybody else at the lab would agree I was guarding it instead, for a full hour or more. It was absolutely worth the wait! When we converted my time lapse into a shorter movie, we were able to observe some very interesting events: the posterior midgut could be observed invaginating, the cephalic furrow could be seen formed and the germ band could be observed to be extending. All of this is indicative of gastrulation, a process that results in the forming of the three germ layers.

As if the excitement at having captured something this significant through a foldscope wasn’t enough, we went one step further and compared the time lapse I had taken to Philipp Keller’s time lapse of Drosophila embryogenesis through a light-sheet microscope. The euphoric feeling I felt when I saw the stark similarities between the two videos up until germ band retraction (which is where my video came to a stop, unfortunately) is unexplainable! We had captured something truly remarkable and beautiful, and I am so grateful that I could have been a part of it.

Rahul Kumar and Gokul Madhav helped me with the experiments and compiling the videos. This module of the course was conducted by Sonia Sen.

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