Georg Halder

Always driven by curiosity

As a teenager he translated hieroglyphics and built a liquid engine. Later, as a PhD student in Walter Gehring’s lab, he bred some weird flies with eyes on their legs. Georg Halder has always been driven by curiosity, and on his map of research there are still many “white spots” waiting to be explored. Apart from science, he is also fascinated by the unknown and the foreign. He loves travelling to discover the secrets of lost cultures and meteorites in the desert.

Alumninews: You studied biology and have worked in research for more than twenty years. Were you born with a passion for nature and life?

Georg Halder: I think I was always curious. Experimenting and finding out how things work have always been a passion of mine. As a teenager I was very interested in physics, chemistry and biology. Finally, I decided to study biology because living organisms are much more interesting than dead matter. Nevertheless, physics is actually very cool too. I like quantum mechanics and modern optics and sometimes I read some exciting articles that come from this field.

Did you already do some experiments when you were a child?

Yes, of course. My godfather was a physicist at the ETH and I visited him in his lab several times. He had some powerful lasers that could punch a hole in paper. I still vividly remember that for my birthday he gave me a subscription to “Scientific American”, a journal, which explains biology, physics, etc. in lay terms. They always published an experiment of the month, which one could do at home. One of these experiments described how to build an engine with a liquid piston. That was great. So, I built this machine and, surprisingly, it really worked. As a teenager I also had a motorcycle, so you can imagine, I did a lot of experiments to make it faster (he laughs).

In the 1990’s you did your PhD in Walter Gehring’s lab. What impact did this time have on your subsequent career?

The time in Walter’s lab was very important for me. At that time, the lab was still in its heyday and very active with lots of postdocs. We always discussed science very intensely. It was a place where you could feel that important discoveries were being made. And Walter had this great passion for biology. He always tried to understand how things work, but he could also see the beauty in nature. He was a true biologist and could infect people with his passion. There is no question that I did benefit a lot!

You bred Drosophila flies with extra eyes on their legs and wings. Was this experiment the key to success?

Yes, it definitely shaped my career. We published a very high ranking paper about this experiment and I was awarded several prizes, which opened some doors, for instance, for fellowships. But my work also raised a lot of attention and many ethical and philosophical questions. I can still remember the day when I first saw a fly with an ectopic eye. I thought: Wow, it’s just crazy, an eye growing on a leg!

What exactly was the response, especially of the non-scientific community?

There was also a big reaction from the public. A newspaper in the USA, the “New York Times”, wrote: “With a new fly, science outdoes Hollywood.” Another journal headlined: “Frankensteinian science at its best.” For them it was like science fiction. Also, when we published the fly with the extra eyes, somebody sprayed on the Biozentrum wall “Let the fly free.” It was very interesting for me to see that the first reaction was mainly fear and uncertainty but once the people understood its implications for biology, they could see the value of this experiment. That’s why I think it is very important to communicate research. With the development of new techniques and therapies, for example in regenerative medicine, we are going to be faced with many decisions and we should make them from being informed.

Right after your PhD you moved to the United States and lived there for 16 years. Why did you decide to come back to Europe?

At first, I didn’t want to return to Europe because living and working in the US was wonderful, but I couldn’t reject the great offer from the KU Leuven (Katholieke Universiteit Leuven). For me, it was an opportunity to start a new project.

For more than two decades you have done research in the field of organ growth. What sparked your interest?

There was one really mysterious question that was always driving me: How do organs know how big to grow? In one of his lectures, Walter Gehring introduced us to some regeneration phenomena, such as seen in the cockroach leg. You can cut a piece of their leg and they can exactly regenerate the missing part. I was really fascinated by all these completely unexplained phenomena. So, when I started my position at Anderson Cancer Center in Houston, Texas, I thought let’s try to work on growth control. So, I did a screen with my colleague and we found a number of Drosophila mutants with abnormal sized organs. One of those mutants we called Hippo.

Why Hippo?

There is the tradition of naming Drosophila genes after animals, which in some way reflect the phenotype, and the Drosophila Hippo mutants look like a hippo. They have big heads and many wrinkles and they are heavily pigmented. Hippo was a very fitting name. 

What impact does the Hippo pathway have on growth and development?

Over the years my lab, and others too, found more components of this pathway and that changes in Hippo signaling lead to changes in the cell number of an organ. What we know so far is that Hippo is required for organ size to be controlled properly. This pathway also seems to have an instructive role for regeneration because without Hippo organs can’t respond to injury. Still, we don’t know what regulates the pathway. We also showed that the Hippo pathway is involved in tumor development. The downstream components of the Hippo pathway become strongly activated in many different tumors and in their absence, a mouse liver can no longer develop tumors. The question is what does deregulated Hippo do in tumor cells that they cannot normally do? So, there is still enough to keep working on.

In the mid 1990’s you received a prize. With the money you wanted to travel to the desert to look for meteorites. Did you make your dream come true?

Yes, I really did this. Right after winning the prize, I traveled for one month to Libya and to the Sahara. Libya – what a beautiful country. Actually, we didn’t go meteorite hunting but our driver gave us a special gift, a piece of Libyan glass. About 20 or 30 million years ago, the tail of a comet impacted the Earth there and melted the sand to form what is known as Libyan glass. 

Are you still interested in ancient Egypt and hieroglyphics? 

I don’t study hieroglyphics anymore but as a teen I did. I also took classes for few years. A couple of times we went to Egypt, we visited the temples and translated the hieroglyphics on the walls. For me, it was also fascinating to be confronted with artifacts from a culture that is completely alien to me. At one of our campsites in the Sahara we found an ancient kitchen about 10,000 years old with household stuff, such as a stone plate, stone knifes and a sharpening tool. I just thought, wow, some people made these thousands of years ago and now you are here. It is simply amazing. Then you realize these few artifacts are the only connection to ancient times.




Since 2012, Georg Halder has been Professor of Genetics at the University of Leuven and the Flemish Institute for Biotechnology (VIB) in Belgium. He studied biology at the Biozentrum and received his PhD under the supervision of Walter Gehring in 1996. He discovered a master control gene for eye development in Drosophila. Subsequently, he worked as a postdoc at the University of Wisconsin. Prior to his current position, Georg Halder was Associate Professor at Anderson Cancer Research Centre, University of Texas in Houston. In his research he focuses on the Hippo pathway and its role in growth control, regeneration and tumorigenesis.