A day in the lab of a cancer researcher: fly geneticist
A couple of weeks ago we highlighted Dr Allison Bardin's work on fruit flies. We've been fascinated by these tiny creatures and how they are used in cancer research. To help us learn more, we continue our day in the lab series with fly geneticist, Dr Kasia Siudeja.
9:00 I usually start my morning by spending some time in front of the computer. First I have a quick look at any new scientific publications relevant to our research. It’s essential, and it allows me to stay up to date with a quickly developing research field. Besides, you never know, it may bring some new ideas for my project…
I also need to check my e-mails. Good news today! Our collaborators, with whom we will perform technically challenging DNA sequencing experiments, have received the samples I sent them, and are ready to start the sequencing project. This is exciting!
For the last two and a half years we have been using our Worldwide Cancer Research grant to study how aging adult fruit fly (Drosophila melanogaster) intestinal stem cells accumulate spontaneous mutations. These mutations lead to changes in the stem cells’ genetic information, and to the formation of spontaneous neoplasia – a pre-cancerous state in the tissue. Performing the whole-genome DNA sequencing on such pre-cancerous tissue samples allows us to identify exactly what types of mutations are causing neoplastic transformation of aging stem cells. This is important because similar changes in the genetic information likely contribute to cancer formation in humans.
10:00 For the next hour it’s time to attend an institutional seminar. Working here at the Institut Curie we always have excellent internal and external guest speakers who share their work on the frontiers of cancer research. Today it’s particularly interesting for me, as we will hear about mechanisms of DNA damage repair in normal and cancer cells.
11:00 Back from the seminar, it is now time to take care of the flies. Working on aging requires good organisation, as every experiment typically lasts a minimum of five weeks. This is the time needed to obtain an aged population of flies. During this time, flies need to be fed regularly (three times a week) and maintained in controlled conditions (25˚C and set humidity). In the lab the flies normally eat a mixture of sugar, yeast and flour, solidified in agar. I give the flies fresh food, and make sure they are doing well. This involves checking that they have not caught bacterial infections, or that too many have died.
Today, one of my fly populations has reached the age of five weeks – they are ready for dissection in the afternoon.
12:30 Time for lunch. Chatting with colleagues during lunch is always great, and a fun way to keep a good team working spirit in the lab.
13:00 In order to analyse the intestines of my aged fly population, I first need to carry out tissue dissections. This requires some manual skills [as you can see on the right, the flies are very small] … and patience! First the flies are anaesthetised with CO2 gas. I will use a dissecting microscope and a set of sharp tweezers to dissect around 150 fly intestines today. This is a lot, but I know that what I’m looking for, the spontaneous intestinal neoplasia, only appears in around 10 percent of these aged flies, so these high numbers are crucial. The dissection will take most of the afternoon.
Directly after the dissection I quickly “fix” the intestines (this involves soaking the intestines in a chemical mix, which acts as a preservative). I then prepare them for a two-day-long staining protocol. This staining means that I will use known markers that will “paint” different cell types of the fly intestine and allow me to look at the different structures and shapes within the intestine (pictured above; you can see the intestinal stem cells, which are green). Afterwards, I will be able to study these “painted” intestines through the microscope to identify the spontaneous neoplasia. I need to count how often I find them, and where they are found along the digestive tract (food pipe) and other interesting features. Tomorrow I will be using the microscope to study all these fly intestines.
17:00 Before I can go home I have one more task on my “to do” list for today. I will set up new fly matings to start a new genetic experiment. Over the last few days I have collected virgin female flies of one genotype, or genetic background, which I now mate, or cross, with males of another genetic background.
This is the beauty and the power of fly genetics in action! In ten days I will collect the offspring of this cross - flies expressing all the components of a genetic system, allowing me to choose whether to slow down or speed up the divisions of adult intestinal stem cells. I will use these flies to see how such changes can influence genetic stability of aging stem cells.
It will take another five weeks for these flies to grow and age sufficiently, but in the meantime I will be carrying out other experiments and analyse results from other matings I set up earlier.
Photo credit: Dr Kasia Siudeja. This is a microscope photograph of section of fly intestine. The blue shows the nucleus of each cell in the intestine; the stem cells are green, and magenta shows us secretory cells (cells that release hormones) called enteroendocrine cells.
The fruit flies were photographed in the lab of former Worldwide Cancer Research grantholder Dr Rui Martinho.
Dr Kasia Siudeja is a Worldwide Cancer Research-funded postdoctoral fellow in the laboratory of Dr Allison Bardin at the Institut Curie in Paris, France, where they are using fruit flies to understand how cancer begins.