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It was 45 years ago that Charline Walker found herself working on zebrafish.
As David Grunwald recalls, "Charline was the perfect partner to work with George Streisinger in his efforts to get an ambitious longterm undertaking off the ground. Charline was devoted to the vision of what they might accomplish with the zebrafish, and she had the combination of patience and technical precision needed to develop a field from scratch. She was/is meticulous as an experimentalist. When George died, Charline held the intellectual and technical memory of all that had been tried, from methods of mutagenesis, genetic tricks, and karyotyping, to fish husbandry. Within the community of laboratories at Oregon and around the world, Charline would travel and teach others and share her knowledge. As importantly, Charline’s natural warmth and her patience with all types of ambitious young scientists aided her effectiveness as a teacher of techniques and as a founder of our community. Her talents, vision, and generosity were critical to both maintaining the field after George’s death and to molding its trajectory."
She was recently interviewed about the early years developing zebrafish as a genetic model with George Streisinger at the University of Oregon, as well as her reflections on her career and the current state of the field.
How did you end up working on zebrafish?
I was a technician in the Institute of Molecular Biology at U of O, studying the termination of protein synthesis with John Menninger who was moving to another university. I started looking for a job and two were available at the time - one on yeast and one on fish. I decided I wanted to work on something I could see for a change, instead of isolating parts of things, so I took the job with George. He had already started raising fish but the project was stalled because of problems with disease.
What was your initial role?
I was the lab tech- though George and I shared fish husbandry jobs on weekends and weekdays. It was hard. We tried several kinds of things to combat the velvet disease, but some things that would directly cure the fish, mutagenized them. We had a whole batch of fish that we essentially mutagenized and made a mess! Eventually, we figured out a treatment that worked.
Do you remember the first time the fish laid and you actually saw embryos?
Yeah, well not specifically. But I do remember being so thrilled to watch them develop that I spent a whole day watching a fish hatch. It took its time! I just sat there and watched it and, finally, it burst out of the chorion- it was so amazing.
How did you start the genetics project?
We learned how to do in vitro fertilization first thing, to get sperm and squeeze eggs. I think George was influenced by frog models (and axolotls) so the idea of early pressure was kind of from that. George was T4 phage, right? He studied intensively frameshift mutants. He wanted to apply those molecular techniques to a vertebrate. And so that’s where the idea of making haploids came from because diploidy was an obstacle. And then he realized that if you could prevent the second meiotic division, you could make diploids.
George was interested in visual behaviors initially?
He chose the visual system because he wrongly thought that an animal could survive without it. Therefore, you could do all kinds of mutagenesis and change all kinds of things and the animal might survive.
Why do you say wrongly?
Because zebrafish are so visually dependent that they would starve to death if they can’t see, can’t catch prey. The reason he chose the visual system was because it was organized so regularly and he figured you could see a disruption of the pattern easily in something like the retina. And he figured defects were not going to be lethal.
Interest in the zebrafish model rapidly increased. What do you think the turning point in the field was for you?
When Chuck (Kimmel) said he didn’t have to go out and promote zebrafish anymore.
Can you think of one highlight in your career, of all the mutants you studied and all the people you worked with, is there one time that really stands out as being especially meaningful?
I guess my most important project was trying to map a mutant that I had taken over in Chuck’s lab, —well, manx.
So you learned how to do recombination mapping?
Yes. The gene turned out to be knypek, which encodes a glypican. Lila’s (Solnkia-Krezel) post-doc had the same thing and basically did the cloning. The phenotype is so cute. Just to watch the convergence problem, the morphological phenotype, was exciting.
Is there one time or experience over your long career that was particularly challenging for you?
Well, more recently, the confocal microscope – not master it—just to not have a nervous attack every time I use it!
I think he would be thrilled.
Do you think he’d be surprised at how many people are working on zebrafish?
The amount of interest and number of labs would surprise him.
I just think of him as looking down on us and being very pleased.
There are so many young people in the field who hear the name George Streisinger, but know nothing about the man. Is there anything you want to share about him?
Well you know, he was a gourmet chef, a goat judge, a fish hobbyist and an all-round wonderful person. And he had a vision. I think he was so brave. I remember how nervous he was when he changed fields from something that he was established in to something that was right on the edge, and I know that his peers were judging him. It took him 10 years to write that first paper. Zebrafish were so unknown.
Would that be the final advice you’d give a young researcher starting out to be a risk taker and not worry about the consequences
No, no, I wouldn’t say that! I think it takes a very special person to do that.
Clearly you believe now that you made the right decision to choose zebrafish over yeast, I am guessing.
Interview conducted by Marnie Halpern