The people behind the papers – Vahid Zadmajid and Daniel Gorelick

Vahid Zadmajid (left) and Daniel Gorelick (right)

Dan, what are the questions your lab is trying to answer?

DG: My lab seeks to understand the molecular and genetic mechanisms by which environmental factors influence embryonic development and physiology, using (mostly) zebrafish as a model system.

Vahid, how did you come to work in the lab and what drives your research today?

VZ: I have always been fascinated by the zebrafish model because of how cool the zebrafish is and the incredible tools developed globally for testing drugs, chemicals and genetic mutations in vivo at an unmatched scale compared to other animal models. In 2021, I joined the Gorelick lab at Baylor College of Medicine because I was fascinated by the lab's research, which tackles big-picture questions and concepts related to non-canonical steroid signaling pathways. Specifically, I was intrigued by how membrane-associated androgen signaling influences embryonic development and organ formation. Today, my research is driven by the opportunity to expand our understanding of how membrane proteins function during early embryonic development.

What is the background of the field that inspired your work?

DG: In 2017, we found that exposing zebrafish embryos to estradiol increased their heart rates and, intriguingly, that this effect was mediated by the membrane estrogen receptor GPER, not by nuclear estrogen receptors (Romano et al., 2017). This discovery opened up new questions about how steroid hormones could influence physiology through membrane-initiated pathways. While there's been significant interest in membrane estrogen signaling, much less is known about membrane androgen signaling. Reports in the literature have shown that androgen exposure in zebrafish embryos cause morphological phenotypes, though the mechanisms have remained a mystery. Inspired by our findings with GPER, we hypothesized that similar membrane androgen receptors might be responsible for these androgen-induced phenotypes, driving us to investigate their role in embryonic development.

Can you give us the key results of the paper in a paragraph?

DG: We identified GPRC6A, a G-protein-coupled receptor, as a key mediator of non-genomic androgen signaling in zebrafish embryos. Using a chemical-genetic screen, we found that exposure to testosterone, dihydrotestosterone or androstanedione causes cardiac edema and tail abnormalities, independently of the nuclear androgen receptor (AR). By creating targeted mutations in gprc6a, we observed a significant reduction in cardiac edema following testosterone exposure, establishing GPRC6A as the primary mediator. To confirm this role, we treated wild-type embryos with GPRC6A antagonists, which blocked testosterone-induced cardiac defects. Through RNA sequencing, we identified Pak1 as a downstream target of GPRC6A, and overexpression of pak1 partially rescued the testosterone phenotype. Our findings reveal a previously unknown GPRC6A-dependent signaling pathway through which testosterone influences cardiovascular development in zebrafish embryos, shedding light on the mechanisms of non-genomic androgen signaling.

Vahid, when doing the research, did you have any particular result or eureka moment that has stuck with you?

VZ: One of the most memorable eureka moments was discovering that testosterone causes cardiac edema in zebrafish embryos through the GPRC6A receptor, independently of nuclear androgen receptors. This finding was unexpected and opened up new avenues for understanding non-genomic androgen signaling, which could have significant implications for developmental biology and medicine.

And what about the flipside: any moments of frustration or despair?

VZ: There were certainly moments of frustration, particularly when initial experiments were conducted using different chemicals to screen embryos and find a reliable and stable phenotype for each chemical exposure. Additionally, one challenging period was troubleshooting the CRISPR-Cas9 mutagenesis efficiency. Ensuring that the guide RNAs were effectively inducing mutations required a lot of optimization and repeated trials. However, these challenges were ultimately rewarding as they led to more robust and reliable experimental outcomes.

Why did you choose to submit this paper to Development?

DG: We submitted our paper to Development because it's widely respected as the top journal in developmental biology, known for rigorous peer review and a focus on quality science. We also love that Development is published by a nonprofit company, The Company of Biologists, that prioritizes science over profit and uses academic editors who are active researchers and know the field. Plus, there's a rule of thumb: the fewer words in the journal's title, the more prestigious the journal – sorry, Developmental Cell!

Vahid, what is next for you after this paper?

VZ: I will conduct my future research on identifying orphan ligand-receptor relationships using a chemical-genetic screening platform. However, current techniques for identifying direct receptor-ligand interactions remain limited. I plan to increase throughput and move to a multiplexed CRISPR gene disruption method termed Mic-DROP. The plan is to screen hundreds of genes to enable large-scale functional genetic screens in zebrafish. Most importantly, I am excited to apply for a tenure-track assistant professor position to continue my exciting journey in the field.

Dan, where will this story take your lab next?

DG: This study opens up some exciting new directions for us. Now that we've shown that GPRC6A mediates non-genomic androgen signaling affecting heart development, we're interested in identifying other proteins that may act as membrane androgen receptors and exploring whether they have unique roles in embryonic development (of course I will defer to Vahid and won't work on anything that he wants to work on as an independent PI). Another exciting avenue is using zebrafish to search for membrane glucocorticoid receptors – if they even exist – and determine if they play a role analogous to membrane androgen receptors. Any membrane steroid receptors we discover in zebrafish could become key candidates for affecting steroid signaling in other contexts, such as hormone-dependent cancers and other diseases where steroid pathways play critical roles. Ultimately, we aim to map out non-genomic steroid signaling pathways and understand how they influence normal development and the progression of diseases driven by steroid signaling.

Finally, let's move outside the lab – what do you like to do in your spare time?

DG: In my spare time, I love singing with the Houston Symphony Chorus. Like lab work, choral singing requires precision, but it's applied in a different way – focused on blending voices and timing to create harmony. Unlike lab work, though, it's all about emotion and teamwork, which helps me find balance. Plus, it brings me great joy.

VZ: If you have little kids, what spare time do you have? That said, running along Brays Bayou in Houston can be restorative.