The mitotic kinase Aurora A has been shown to regulate the anterior-posterior polarity in developing Caenorhabditis elegans embryos. In a new study, Daniel Dickinson and colleagues find that Aurora A has temporally distinct roles in coordinating the localization of Partitioning defective (PAR) proteins to establish cell polarity during development. To find out more about the story behind the paper, we caught up with first author Nadia Manzi and corresponding author Daniel Dickinson, Assistant Professor at the University of Texas at Austin.

Daniel Dickinson (left) and Nadia Manzi (right).

Daniel, can you give us your scientific biography and the questions your lab is trying to answer?

DD: We're interested broadly in how cells respond to developmental cues and adjust their behaviour accordingly. Our specific focus is on cell polarity, a cell behaviour that is very context-dependent and crucial for normal development. We want to understand at a basic level how cells polarize, but also how they coordinate their polarity with what's going on around them in an embryo. In terms of my background, polarity is a topic that's fascinated me ever since I was joint Ph.D. student in the labs of Bill Weis and James Nelson at Stanford. There, I identified and studied a form of epithelial polarization in the social amoeba Dictyostelium. I went on to Bob Goldstein's lab as a postdoc, where I learned to use C. elegans embryos, which are a classical polarity model. I developed CRISPR and ex vivo biochemistry tools for worms, and I began applying these new approaches to understand how early embryos establish asymmetry. I started my lab at UT Austin in 2017.

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

NM: As an undergraduate, I had the opportunity to work with advisors, Anne Cress and Jason Yuan, to study the role of integrin in prostate cancer cell metastasis and the role of endothelial-to-mesenchymal transition in pulmonary arterial hypertension, respectively. I then was fascinated by how cells change their behaviour in response to their microenvironment. Entering graduate school, I wanted to focus on mechanisms that govern cell behaviours, such as cell polarity and differentiation. I joined the Dickinson Lab to take advantage of the multi-disciplinary approaches and tool development to study cell polarity in different model organisms. The Dickinson Lab is also a diverse and inclusive lab which provides me the opportunity to interact and learn from people with diverse backgrounds. Additionally, Dr Dickinson is an incredible mentor who dedicates his time to ensure that students develop both research and professional skills. Currently, I am interested in deciphering how polarity proteins coordinate with cell cycle kinases to understand how the early embryo generates cellular diversities, a crucial event during early development.

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

DD: Shortly after the lab was founded, in early 2019, there was a set of four really nice papers from the Gönczy, Goehring, Motegi and Kotak labs that implicated Aurora A, a kinase found at the centrosome, as a key factor for the initial symmetry breaking event that established polarity in the C. elegans zygote. This was exciting because, although centrosomes had been known to be crucial for symmetry breaking for a long time, the identity of the centrosomal molecules involved had been unknown. However, although all four papers agreed that Aurora A was important, its mechanism of action remained unknown. Further complicating matters, there was a confusing spectrum of phenotypes caused by Aurora A RNAi that all of the papers reported to varying degrees: some embryos failed to break symmetry entirely, whereas others appeared to have extra symmetry breaking events that led to bipolar embryos. We started working on this because we were fascinated by this complexity and motivated to try to understand mechanistically how it came about.

We started working on this because we were fascinated by this complexity and motivated to try to understand mechanistically how it came about

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

NM: In this manuscript, we have shown that a cell cycle kinase, Aurora A, regulates polarity proteins differently at different time of the cell cycle. In C. elegans, anterior-posterior polarity is established at a zygote stage by localizing polarity proteins at their respective anterior or posterior domains. We showed that in meiosis I, Aurora A prevents the later formation of bipolarization or reverse polarity, whereas in meiosis II, Aurora A is required to break symmetry. Furthermore, we showed that this dual role is unique to Aurora A because perturbation of another mitotic kinase, PLK-1, at meiosis I or meiosis II results in similar phenotypes.

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

NM: The result that stuck with me the most is how degrading Aurora A early in the germline and later in the cell cycle results in two distinct phenotypes. This is particularly fascinating because we initially did not believe that auxin-mediated degradation of Aurora A was going to work in a timely manner as the C. elegans embryos develop fast (in a span of minutes). It was especially gratifying that these experiments were first performed and proven to work by my undergraduate mentee, Bailey de Jesus, when I was out of lab sick.

A polarized C. elegans zygote with endogenously tagged Aurora A (green) and polarity protein PAR-2 (magenta).

A polarized C. elegans zygote with endogenously tagged Aurora A (green) and polarity protein PAR-2 (magenta).

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

NM: In the early days of performing the experiments to inhibit Aurora A kinase activity using inhibitors, I imaged embryos treated with inhibitors and they showed a completely different phenotype compared with the RNAi phenotypes: these results were very exciting because they suggested that Aurora A may be regulating polarity proteins via distinct mechanisms. The next day, I imaged the DMSO-treated control embryos and they showed similar phenotypes to the inhibitor-treated embryos. I was frustrated and disappointed because I reasoned that the phenotypes observed in inhibitor-treated embryos were likely resulting from DMSO toxicity. Later on, I realized that the way these embryos were mounted was making control embryos sick, which impacted the resulting phenotypes. I found a mounting strategy to allow the DMSO-treated control embryos to polarize normally, which allowed me to see the effects of inhibitor treatments clearly.

Why did you choose to submit this paper to Development?

DD: We've always held Development in high regard: the papers published there are consistently interesting, focused, rigorous and make important contributions to the field. The journal also is targeted at the audience we want this paper to reach. We published our first Development paper last spring, and it was a really good experience.

Nadia, what is next for you after this paper?

NM: I am still excited to study the coordination of cell polarity and cell cycle regulators. I have now shifted gears to study how mitotic kinases affect polarity proteins in mouse embryonic stem cells (mESCs) as they can recapitulate polarization events that occur in the early embryo. I am currently using a CRISPR gene editing approach that our lab recently developed to tag polarity proteins in mESCs, in combination with the auxin inducible system, to understand how polarity proteins coordinate with cell cycle in early mouse development.

Daniel, where will this story take your lab next?

DD: We continue to be interested in the different ways that embryos modulate cell polarity and the mechanisms that operate in different contexts. One thing we did not really address in this paper is the mechanism of action of Aurora A – exactly what substrates does it phosphorylate that leads to symmetry breaking? We know now that it probably has different substrates in the germline compared with the early embryo, so that narrows the problem a bit, but this is still an exciting question for the field in the near future.

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

DD: I spend most of my free time camping, hiking and biking with my wife and two boys, who are 9 and 12. I also love to cook.

NM: In my free time, I like to spend time with my family and friends, and I love swimming.

N. I.
de Jesus
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Temporally distinct roles of Aurora A in polarization of the C. elegans zygote