Ear Notches: Trash or Treasure?

Our newest reindeer calf’s DNA will soon be part of our Frozen Zoo.

We have over 8,500 individual animal cell lines represented in our Frozen Zoo®, a cell line collection started in 1975 by San Diego Zoo Institute for Conservation Research founder Kurt Benirschke and his laboratory technician, Arlene Kumamoto. They started establishing cell lines on what was an easy source of material at that time: ear notches. The San Diego Zoo Safari Park had just opened a few years earlier and was home to many hoofed animals (deer, gazelles, antelope, oryx). All of these animals were ear notched as a way to identify individuals out in the field (see post Picking One from the Herd). These small ear-notch pieces were put into vials with a transport media, instead of being disposed of, and taken back to our Genetics Laboratory.

A vial containing an ear notch sample in transport media.

We still receive many ear-notch samples each year on hoofed animals new to our collection. Once we have the samples at the laboratory, the ear notch is processed and set up. We log in all of the information on the animal—species, common name, identification number, and birth date—into the Frozen Zoo database. Then the sample is taken into our tissue culture laboratory and, while working in a biological safety cabinet, or “hood,” the sample is set up. To do this, we first clean up the ear notch by removing any hair or debris. Then we cut the sample into very small pieces, and the pieces are covered with an enzyme and put into an incubator for around four hours to digest.

An ear-notch sample is processed in our Genetics Lab.

Next, when the sample looks digested, it is put into a flask (a sterile tissue culture vessel), and a special media is added and then incubated. In the next 72 hours, we hope to see cells attached to the bottom of the flask. These cells will then start to divide and grow for about three to four weeks until we have enough cells to freeze and make this animal part of the Frozen Zoo’s cell line collection. At this point, we have this animal’s DNA saved as a living cell line. At any time we can thaw a vial of cells and put them back into the incubator, and they will start to grow and divide again.

Fibroblast cells from a Siberian reindeer.

Recently, we received an ear notch from our Siberian reindeer calf. We have his cells growing, and soon his DNA will be part of the Frozen Zoo. Even though I have seen the start of many cell lines, it still seems like magic when you see those first cells start to grow and divide. What species would you choose to add to the Frozen Zoo?

Suellen Charter is a research coordinator for the San Diego Zoo Institute for Conservation Research. Read her previous post, Counting Chromosomes.

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