Professor Dan Bernard is Director of the Centre for the Study of Reproduction at McGill University, Montréal, Canada. Here, he shares his interesting research journey and career highlights with Editor of The Endocrinologist, Kim Jonas.
Please tell us about your main research area
We are principally interested in the endocrine and neuroendocrine control of reproduction. Our major areas of research concern signalling by gonadotrophin-releasing hormone (GnRH), activins and inhibins in pituitary gonadotrophs, and the control of follicle-stimulating hormone (FSH) and luteinising hormone (LH) synthesis.
How did your career bring you to this point?
It has been a long and circuitous journey, and I will try to keep the story as short as possible, though I suppose it might be a useful tale for early stage scientists about following your interests.
As an undergraduate, I conducted two years of independent research studying visual perception in birds. This led to my initial graduate work on auditory perception, again using avian models. However, during my first year of graduate school, I took a course in neurobiology and behaviour, and found myself particularly excited about the section on the neural control of birdsong. It turns out that songbirds have evolved structures (nuclei) in their brains that enable them to both learn and produce song. These regions are sexually dimorphic, as it is typically the males that sing. They are also highly plastic. The regions grow and shrink as singing waxes and wanes. Birds typically sing in the breeding season as their testosterone levels increase. The so-called ‘song control nuclei’ contain steroid receptors, including androgen receptors, and testosterone can drive increases in singing behaviour and volumes of brain nuclei.
Coincidentally, in my second year of graduate school, my department recruited a new investigator who was studying this system. I started a collaborative project between the two labs. By the start of my third year, it was clear to everyone where my interests lay, and I moved to the new lab where I completed my PhD. My research showed that it was the act of singing rather than testosterone that drove the increases in size of the brain nuclei. That is, testosterone made the birds more likely to sing. Singing in turn promoted changes in the brain. This was akin to a muscle growing in response to repeated use.
'When I first heard about single cell omics approaches ... I just did not see how we needed these tools to answer any of our questions. Well, I was wrong.'
For my postdoc, I was encouraged to move to a mammalian system (if I wanted a job in academia). But I was still very much interested in brain plasticity. So, I decided to work on brain changes in seasonally breeding Siberian hamsters. In this species, long day lengths promote activity of the hypothalamic–pituitary–gonadal (HPG) axis. In contrast, the HPG axis is ‘turned off’ under short (winter-like) day lengths. We already knew that GnRH expression was not altered in the brains of these animals, so this suggested there was another mechanism mediating changes in reproductive physiology. We therefore decided to do a differential gene expression analysis of the hypothalami of short- and long-day hamsters. At the time, the methods were primitive by today’s standards. We employed an approach called differential display, which was also known as differential dismay because of the high rate of false positives and negatives! This was my experience, and we really did not pull out anything interesting from the brains of these animals. However, we did note that when we moved hamsters from short to long days, FSH levels went up quickly while LH levels remained low. I became very interested in the differential regulation of FSH and LH. This led to a second postdoc where I focused on the mechanism of inhibin action. Inhibins suppress FSH production by pituitary gonadotrophs. So, this is how I ended up ‘in the pituitary’ where I remain today.
What has kept you interested in the pituitary for so long?
It’s the master gland. Need I say more? In all seriousness, the pituitary is a very interesting tissue. The anterior lobe has five hormone-secreting cell types that control diverse aspects of physiology. My lab is interested in gonadotrophs (FSH and LH) and thyrotrophs (thyrotrophin; TSH).
With respect to gonadotrophs, there was a series of questions I wanted to answer. What transcription factors restrict FSH production to gonadotrophs? How do activins stimulate FSH production? How do inhibins suppress FSH production? In the almost 22 years I have been running a lab, I am happy to say we have answered many of these questions. But, as we all know, answers often inspire new questions, which continue to keep us busy.
Our work on thyrotrophs was a bit of a happy accident. In my second postdoc, I was working on a putative inhibin receptor. It turns out that this protein is not an inhibin receptor in gonadotrophs but rather regulates TSH production in thyrotrophs. Mutations in the gene encoding the protein are the most common cause of central hypothyroidism in people. We continue to investigate how this protein functions to regulate TSH synthesis and secretion.
How have advances such as the omics explosion shaped your research?
It is funny. When I first heard about single cell omics approaches, I did not immediately jump into using them. We are a question-driven rather than method-driven lab, and I just did not see how we needed these tools to answer any of our questions at the time. Well, I was wrong.
We knocked out the putative inhibin receptor in mice and did not get the expected effect. We realised that there must be another receptor but did not know how to identify it. Fortunately, right at that time, another group published the first single cell RNA-sequencing analysis of the mouse pituitary and a new gene popped up (one we had never heard of), which turned out to be exactly what we were looking for.
Since then, we have been very enthusiastic about these approaches and employ them frequently, thanks to vital collaborations with real experts in the field. Using single nucleus ATAC-seq, we identified enhancers for the FSHβ gene that we would never have found without these amazing tools.
What have been your career highlights?
This is a tough one to answer. Personally, my most gratifying moments were earning my PhD, landing my first independent position, getting my first grant, and watching the maturation of my graduate students into scientists.
In terms of scientific discoveries, the top one so far has been the cloning of the inhibin B co-receptor, TGFBR3L. We have another exciting story that we have been working on for several years that should be published in the next year. Stay tuned…
And what are your top three publications (impact factor/citation index aside!)?
This is like asking someone to pick their favourite child. I guess I would rather comment on three papers that may end up having the greatest impact long term. The first is our discovery, with our team of international collaborators, that mutations in IGSF1 cause central hypothyroidism.1 The second was our recent discovery of TGFBR3L as the inhibin B co-receptor.2 This was only published in late 2021, but we think this could have impact in several areas, including in infertility treatment. Finally, there is our discovery that FOXL2 is a selective regulator of FSH synthesis in gonadotrophs.3 As I mentioned, we have a long-standing interest in differential regulation of the gonadotrophins. This was the first demonstration of a transcription factor that uniquely regulates FSH versus LH synthesis.
What papers have inspired you?
In the field, I think I have been most inspired by the first paper that identified betaglycan as an inhibin co-receptor.4 It inspired a lot of my work – as well as my gmail address and Twitter handle (@BetaglycanDan)!
I think the paper that affected me most as a scientist, however, was ‘Strong inference’ by John Platt.5 There are elements that are anachronistic today (it was published in 1964), but it is a blueprint for how to do science. It is a must-read for new graduate students in my opinion. I read it in my first year of graduate school and it still influences me today.
How have your research environment and collaboration shaped your research?
'My most gratifying moments were earning my PhD, landing my first independent position, getting my first grant, and watching the maturation of my graduate students into scientists.'
They have both been very important. We are all shaped by our environment. I have worked on things in my career that I never would have if not for my local colleagues. For example, the Montréal area has many investigators working on G protein-coupled receptors. We might have stuck to transforming growth factor-β family signalling and not looked at GnRH or gonadotrophin signalling if it had not been for the support and encouragement of colleagues.
Collaborations have been absolutely essential to any successes we have had. Collaboration is a win–win situation. When we lack expertise (which is often), we never hesitate to reach out to experts to ask for their help and collaboration. This has led to a lot of new discoveries and friends. We are also quick to help when others think we may be of assistance.
What advice would you give to trainees forging a career in research?
First, follow your interests. Secondly, never marry for money; move where the rich people are and marry for love. The point here is that you should work on what you are passionate about, and it is all the better if it is in a fundable area!
REFERENCES
- Sun Y et al. 2012 Nature Genetics 44 1375–1381.
- Brûlé E et al. 2021 Science Advances 7 eabl4391.
- Lamba P et al. 2009 Molecular Endocrinology 23 1001–1013.
- Lewis KA et al. 2000 Nature 404 411–414.
- Platt JR 1964 Science 146 347–353.
