Alex’s cells growing out of their “clothes”

Alex: I miss seeing my cells. How are they doing?

Birgitt: In the last two weeks your cells have grown a lot. In the image below you can see your skin fibroblasts at a low density. When you watch the cells carefully under the microscope, you can see cells are dividing. I have drawn some arrows that point to these pairs. How many more dividing cells can you find in this picture?

Alex: 1, 2, 3 maybe…more?

Birgitt: To witness how cells grow is always fascinating, isn’t it? In the next two images you can compare your cells on day 20 and day 22 after biopsy. Within two days all the space between the cells is filled up. Once the fibroblasts become dense and touch their growth slows down which is called contact inhibition.

Day 20	Day 22

Alex: What do you do when the cells in the culture dish become overcrowded. You explained last time that you “split” the cells. How does that work?

Birgitt: In order to split the cells, we use trypsin which is an enzyme also found in your digestive system that breaks down proteins. The trypsin treatment is only needed for a few minutes. During that time the cells lift off the culture dish, then they are washed to remove the trypsin, transferred to a larger culture vessel, and replenished with fresh media. During the expansion period, I expand the cells from the original culture dish with a surface area of about 45cm² to three large flasks with a total surface area of 450cm² as you can see in the image below.

Alex: Wow that is a 10-fold expansion. How many cells will you have grown at the end?

Birgitt: In these three flasks are about 20 million of your skin cells. I will freeze them in special hibernation media in little vials at 1 million cells per vial. This stock of your skin cells is the foundation for all downstream experiments. Now, we can start planning the next phase: turning your skin cells into induced pluripotent stem cells, a process called nuclear reprogramming.

Alex: Very excited to learn about it. Thank you.