#LabHacks: The practical single-bristle toothbrush for stroking fish eggs
Robby Fechner rubs his hands with glee. Everything is ready for one of the most important steps in zebrafish research: modifying its DNA. The MDC’s aquatic animal care manager’s workplace somewhat resembles a picture puzzle. Three items, seemingly unconnected, lie on the table next to each other: a dish containing a blue gel, a paint brush and a toothbrush with just one bristle. The paint brush and the single-bristle toothbrush play a small, but crucial, role in the process.
A soft bed of gel
“To modify zebrafish genetically, one of the things we do is to microinject foreign DNA into the egg at the earliest possible stage before it develops into a fish,” Robby Fechner explains. The eggs start to divide just 45 minutes after fertilization – so the researcher has to work quickly.
As soon as the eggs are laid, they are placed on a jelly-like solid gel It has a number of grooves, each of them shaped like a little ramp. The gel grooves are only minimally wetted and the eggs are lined up in them so that they cannot roll off during the injection procedure.
Aim well!
Enter the single-bristle toothbrush: “We use it to turn the fish eggs so that we can inject them in a specific spot,” says Robby Fechner. In times past, he and the researchers used to use tweezers which often damaged the sensitive fish eggs.
The position of the eggs is extremely important. If the injected substance does not penetrate the nucleus of the egg, the DNA does not appropriately integrate into the genome. Robby Fechner has to hit the nucleus head on to produce permanently genetically modified fish. When giving the injection itself he guides a fine glass capillary through the egg’s strong protective membrane, the chorion, and gently holds it still with a fine, soft hair paint brush.
The single-bristle toothbrush was a gift
When the injecting has been completed, he floods the gel ramp with water and carefully pushes the eggs into a Petri dish. After being transferred to an incubator, they continue to develop until they turn into tiny zebrafish in just a few hours.
Robby Fechner, incidentally, did not invent the single-bristle toothbrush, it was a leaving present from one of his trainees. One of the animal keeper’s many sayings for teasing MDC’s trainees in aquatic animal care is that they will have to clean the lab with a single-bristle toothbrush. Now Robby Fechner has one of his own – but it is much too good to use on the lab floor.
Images: MDC
