preLights talks to Christian Mosimann

2 June 2021

Christian Mosimann is the Helen and Arthur E. Johnson Chair for the Cardiac Research Director and Associate Professor of Pediatrics at the University of Colorado School of Medicine, Anschutz Medical Campus. His lab predominantly uses the zebrafish (Danio rerio) to investigate the lateral plate mesoderm and developmental and evolutionary origin of the cardiovascular system. He is a big proponent of preprints, having posted his lab’s first preprint on bioRxiv in 2016, and his research has also featured on preLights. We caught up with Christian to discuss his initial interest in science, research career, and views on preprints.

Back to the beginning – where do you think your interest in science came from?

My parents aren’t academics, and research as a profession wasn’t something we ever talked about when I was a kid. I did have constant access to plenty of good books with pictures of animals and TV documentaries. We would go to Greece every summer to visit my mum’s family, and being immersed in nature and wildlife at the ocean triggered a lot of interest. What I did become increasingly interested in throughout my education was the common things between living organisms, and it took me a while to realise that molecular biology is what ties all life together. Even now, getting to the fundamental principles of processes that happen in living systems is what fascinates me. So, when I started university, I really wanted to continue and get deeper into this aspect of biology.

And this led to starting a PhD?

I took a laboratory course towards the end of my undergraduate degree, and, to be honest, that course was quite soul-crushing for 3 weeks. It was very disconnected: molecular cloning, bacterial transformation, all kind of blotting methods, with no concept or connections between the experiments. But in the last week, we had a section on model organisms co-run by Konrad Basler’s lab, and I straight away became fascinated by how model organisms can be used to deduce molecular mechanisms and how they contribute to development and patterning. When I started my master’s thesis, I knew that his lab would be the right place to get into these topics.

When I showed up on my first day and went to his office, Konrad pushed two tubes of flies towards me and explained that the lab had found an interesting phenotype that I should start investigating. Classic reverse genetics experiments – we knew there was a transposon integrated next to an unknown gene, so I worked on linking the affected gene to the phenotype. Eventually this ‘first’ project that was supposed to fill my master’s thesis led to my PhD project and to me getting into transcriptional regulation and nuclear Wnt signalling in Drosophila. I realised years later that Figure 1 of my first paper entailed my entire master’s thesis, and it’s quite sobering to think that a whole year’s worth of research went into one figure. I still joke with Konrad that I’m waiting for my real PhD project, not just the continuation of my master’s!

What stayed with you from your PhD experience?

I struggled early on with the fact that nobody is going to tell you when something is correct and valuable, and maybe you don’t even know straight away that an interesting phenotype might be important. This is an interesting aspect of science to discuss, especially with graduate students. I think they often think that you get the grant funding, all the pieces fall together, and it’s like the heavens open and the angels sing. But that’s not the way it is at all. Especially at the beginning, lab work is more like a string of small events, and eventually you develop a bigger perception of how your science evolves over time. I didn’t know how to define this all until I read a paper by Daniel F. Chambliss on ‘The Mundanity of Excellence’ that describes how stringing together seemingly mundane details can lead to excellence, and that opened my eyes completely. When you can do the day-to-day tasks without too much thought, that’s when you can start seeing the big picture and see how these small findings all add up.

And after your PhD you switched from Drosophila to zebrafish. Was it a conscious decision to move into vertebrates?

I realised that Drosophila was great as a simplified model for basic patterning, for example, if you’re working on wing discs and signalling pathways, but what I really wanted to do next was apply my molecular training to a bigger, more complicated system. And very early on in my reading I stumbled across the fact that blood is a very weird organ; it’s not a solid organ that grows, it’s an accumulation of cells with similar patterning that eventually flows, and I found that oddity in how blood forms very interesting. The zebrafish as a model for blood development is particularly fascinating because its development happens so quickly – within 24 hours you have a beating heart and a circulatory system. Plus, I’ve always liked microscopy, so moving into a model that’s amenable to imaging was also exciting to me. So that’s how I got into fish: it’s genetically tractable and you can work on it with imaging too.

It also seems like your career is a clear path of progressing from basic research during your PhD to something that’s more translatable during your postdoc.

When you work on Wnt signalling, the biggest link to translatable research is easily colorectal cancer and cancer in general, but that link is often lost on people when you tell them you work with flies. After my PhD I felt I had the opportunity to get into vertebrates as a way of balancing basic and translational research for myself. It was also interesting to move to a clinical environment for my postdoc in Leonard Zon’s lab at Boston Children’s Hospital. It’s a huge benefit to have clinically trained colleagues, but it does somewhat put the importance of your miniprep into perspective when you know they’re treating children with cancer.

And did that inform your research objectives?

When I started with Len he already ran a very big lab – more than 30 people – so it was very easy to feel lost early on, but I knew that I wanted to use my skills from Drosophila to develop transgenesis tools in zebrafish that would answer the types of questions I was interested in: isolating regulatory elements, genetic lineage tracing, looking at cardiovascular development, and eventually working on lateral plate mesoderm and neural crest cells. When we were junior postdocs, my colleague Charles Kaufman was interested in melanoma, so together we started to look at the crestin gene, which is only active for the first day or so in early neural crest cells. We developed a GFP reporter for crestin and eventually realised it would actually label initiating melanoma tumours as green glowing before you even noticed them, and that became an extensive story over time. Similarly, I spent a long time trying to define early hematopoietic cells with different transgenics before focusing on draculin. This odd gene was already known for producing beautiful in situs of early hematopoietic cells, but it turns on during gastrulation – much earlier than other hematopoietic markers – something nobody quite knew back in the day. I generated a draculin:GFP reporter, and it marked different blood and endothelial lineages as stripes along the edge of the developing embryo, almost like the seams of a baseball, yet the reporter expression also included kidney progenitors and cardiac progenitors. I’d inadvertently stumbled onto the complex biology of the lateral plate mesoderm, and I was fascinated by what tied all these different cell types together so that all of a sudden the cardiovascular system, the blood itself and more are all coming out of this mesodermal domain. And from there I began to build up my independent research program.

Could you tell us about your transition from postdoc to PI?

I got the opportunity to go back to Switzerland for a Swiss National Science Foundation professorship in 2012/2013 and it felt right at the time. I was fortunate to recruit some very talented people right away, and my first students Anastasia Felker and Christopher Hess were the driving force behind our first projects (on Tamoxifen metabolites for CreERT2 control  and smooth muscle differentiation in vertebrates) and larger collaborations. My wife, Alexa Burger, joined the lab too and she initiated all of our CRISPR-Cas9 work together with our first master’s student Jonas Zaugg. We were also very lucky to soon get access to a light sheet microscope for live imaging and to start developing some powerful collaborations (on cardiac progenitors in zebrafish and emergence of the lateral plate mesoderm in chordates), which have led to long-lasting good friendships. But my family and I did long to go back to the US and also to work back in a medically affiliated environment. Serendipitously, the opportunity at the University of Colorado came along and we didn’t really hesitate to move when the details came together. We have brilliant colleagues here, and I’m part of a growing community in the paediatrics department that integrates basic research and the fantastic work of our clinical colleagues. We’re able to look at mutations and phenotypes that can inform us about the development of the heart and cardiovascular system, and that’s really relevant for the children with congenital heart disease right here at the hospital.

To preprints: your first listed paper on bioRxiv was posted in 2016, which is relatively early in terms of preprint uptake. Did you have any reservations about preprinting to begin with?

It was almost coincidental how that happened. At the time we were really investing in CRISPR-Cas9, and our neighbouring lab in Zurich was run by Mark Robinson, who is well visible in the field of bioinformatics and RNA analysis. As we started doing all our CRISPR work, we had the problem of trying to verify our mutations. There were a few software packages that could tell you if the sequences you fed in were mutated or not. But I’m a trained geneticist; I want to see the actual sequence and know the sequence quality. Alexa and Helen Lindsay, who was then a postdoc in Mark’s lab, put their heads together and came up with this really accurate program with a graphics output for looking at CRISPR mutations. We split this work into two papers (one based on wet lab work and one computational , and Mark immediately told me that his lab preprints everything. I had so many questions – how could you just put a research finding online and know if an analysis paradigm works or if experimental results are correct? Mark was very pragmatic and explained that for bioinformatics pipelines, for instance, you can run the script to see that it works – but this was very puzzling to me as you can’t do that easily with ‘wet-lab’ biology. I found it really challenging to think that anybody can put anything they wanted to out there. Eventually though, I agreed we could preprint the bioinformatics paper to see how it went – and in the end it was very well received.

And that encouraged you to start preprinting yourself?

At around that time I was also applying for a grant extension, and I realised that maybe it would indeed be easier to submit the citation of a preprint instead of a letter from the editor of a journal saying that a paper was under review. So I started to see the value in having a preprint out. I only preprint papers that we send out for peer review at a journal and not to stake a claim on something, and I’ve found this to be very helpful for job searches and for grants. Although I was super sceptical at the beginning, now I think preprints are something we should really embrace as a community. I think the more we normalise preprinting our work we are confident in, the more we can show everyone that nobody is going to scoop you the very next morning if you put your research on a preprint server.

How do you view the idea of discussion around preprints in comparison to peer review?

I’ve heard about labs doing journal clubs based on pre-printed manuscripts and sending their comments to the authors, which we haven’t done so far. But I do think it’s refreshing for authors to receive recognition that people are reading their work, and it gives fellow researchers access to data 6 months to a year quicker than they would otherwise see it. I’ve set up a few collaborations that started when other labs saw findings published as a preprint, and I’ve had one or two instances of comments via email but less so openly on social media. I think comments on preprints are not as negative as anonymous peer reviews are at times – most feedback is asking about a certain transgenic or how you made a figure, and I think these are all vastly positive outcomes.

Do you think the benefits of preprinting are the same for an early-career researcher as they are for a more established PI?

This is a good topic and not something that I think is always very balanced in ongoing discussions. If you’re a PhD student transitioning to a postdoc search, then the opportunity to show your work as a preprint whilst it’s still in the publication process is tremendously valuable. Having said that, I don’t think we should put an artificial burden on trainees to have their work preprinted. Ultimately, it’s not their call if the work is preprinted, it’s their PI’s, so we should be sensitive about how labs handle this and not complain or pass quick judgement when students or junior postdocs don’t preprint their work. In general though, I think it has a tremendous benefit to the lab as a whole as you can show productivity right away, whereas with peer review the process is really out of your hands.

And to finish, what piece of advice would you give to early-career researchers who think they’d like to pursue a long-term career in academia?

Again, science is not waiting for a big epiphany. I’d really encourage people to think about what they actually want to do with their lab; I call it the Monday morning test. You start your new assistant professor job, show up on Monday morning at 9 am and have coffee with the department chair, everyone’s congratulating you on your new lab. Then at 9:30 am, you close the door and you’re alone in your office. What happens then? That’s when you need an idea ready, a plan, need to know what the next steps are. I don’t mean we should pressure people into having grand hypotheses from the beginning of their PhD, but it’s a good idea to start thinking in the direction of real deliverables and a research question they are interested in. If you’re going to pursue this after your postdoc position, you’ve got to actually know what your follow-up is.

Christian was interviewed by Helen Robertson, Community Manager for preLights. This interview has been approved by the interviewee.