First person – Eliana Torres-Zelada

Eliana Torres-Zelada

How would you explain the main findings of your paper in lay terms?

When I describe my research to my parents, I always ask them to imagine chromatin as an old-fashioned telephone cord. This chromatin consists of DNA and proteins (called histones) and provides a barrier for gene expression, which is the process by which the instructions in our DNA are converted into a functional product. There are certain proteins or protein complexes, like CHAT (my favorite one), that chemically alter the histones bound to DNA, helping to relax the DNA cord, thereby enabling gene expression. There are other complexes similar to CHAT, such as SAGA and ADA. In our paper, we reveal that these complexes function redundantly in the regulation of gene expression in the Drosophila embryo. We also show that one of the CHAT subunits, Chiffon, not only works within CHAT, but also independently, probably in conjunction with other proteins. Finally, Chiffon is a huge protein, with two regions and functions that are completely separate. Surprisingly, these regions are expressed at different times during embryogenesis. This raises some big questions about how/why these two regions are expressed at different times in flies.

Were there any specific challenges associated with this project? If so, how did you overcome them?

Our ability to characterize the developmental defects in chiffon mutants has been made particularly difficult by the presence of chiffon mutations on the CyO balancer chromosomes, including balancers that are generally used to identify homozygous mutant embryos. To overcome this issue, we used some fly genetic tricks, like the Gal4/UAS system. We generated flies that carry two different chiffon null alleles on the same chromosome as either actin-Gal4 or UAS-10xGFP fusions, and then crossed these flies in order to select GFP-positive embryos that carry the two different chiffon null alleles. Being able to see GFP in early embryos was a challenge too. We tested different drivers and different GFP versions in order to be able to sort embryos successfully. Another challenge when studying gene expression regulation is the amount of material that you need in order to perform high-throughput analysis. It was also a challenge in terms of time to collect the number of embryos needed to perform ChIP-seq studies. We hand-sorted more than 9000 embryos!

When doing the research, did you have a particular result or ‘eureka’ moment that has stuck with you?

The most surprising finding of our study came from our analysis of H3K14ac immunostaining in chiffon versus Ada2b null-mutant embryos. We identified a substantial decrease of H3K14ac in the chiffon mutants that was higher than that observed in Ada2b mutant embryos, suggesting broader roles for Chiffon in the regulation of histone acetylation outside of the Gcn5-containing complexes. This is very surprising, and was a bit of a ‘eureka’ moment, because before this study, we were considering that Chiffon functions in gene expression regulation only as part of the CHAT complex. This is very exciting and raises the question whether Chiffon can act as a co-activator on its own!

Why did you choose Journal of Cell Science for your paper?

Since our work has a combination of techniques ranging from fly genetics and microscopy to high-throughput genome analysis, we were looking for a journal with a broad scope that focused on cell biology questions. We had also published our first paper describing the existence of the CHAT complex in the Journal of Cell Science, so we thought it was nice to follow-up with this second paper, starting to explain the function of the complex.

Have you had any significant mentors who have helped you beyond supervision in the lab? How was their guidance special?

I would like to express my gratitude to my mentor and academic advisor, Dr Vikki Weake, who has given me the opportunity to work in her lab. Since I joined her group in 2016, she has always made time to discuss my ongoing and future experiments. Her enthusiasm, positive attitude, and encouraging words helped during this journey.

What motivated you to pursue a career in science, and what have been the most interesting moments on the path that led you to where you are now?

Like most scientists to be, I was very curious when I was a child. For me, few things in life are as interesting as life itself, ranging from how a single molecule of DNA encodes all the genetic instructions necessary for development, to how cells communicate during development of different tissues and organs. Since I was a kid, I have always been fascinated with biology, and that is why I decided to pursue a career in biology. Because the scientific opportunities are more limited in my home country, Peru, I sought out research experiences abroad and eventually, I ended up at Purdue University in Indiana, USA, where I graduated from the Department of Biochemistry last summer.

What's next for you?

During my PhD period, I studied the role of the Gcn5-containing complex, CHAT, in gene expression regulation. Currently, I have started my postdoc training at University of Wisconsin–Madison under the supervision of Melissa Harrison, and I am working on investigating the role of the pioneer transcription factor Zelda in promoting the undifferentiated fate in neural stem cells in Drosophila larva. After this training, I hope to pursue a career in academia as an independent investigator.

Tell us something interesting about yourself that wouldn't be on your CV

I have a black belt in karate and know how to make a mean ceviche. And on a more creative note, my partner and I do craft painting, combining symbols of our countries. The last project was decorating the puppy toy box of our little Luna.