Stem cells exist within a niche, a microenvironment that regulates their activity, but the mechanisms by which niche cells influence stem cell behaviour are poorly understood. In this issue, Stephen DiNardo and colleagues reveal that the shape of the adult Drosophila testes niche, which is dependent on the cytoskeleton of the niche cells, is crucial to maintaining germinal stem cell function. To learn more about this work, we spoke to first author Gabriela Vida and corresponding author Stephen DiNardo, Professor of Cell and Developmental Biology at the University of Pennsylvania, USA.
Stephen ‘Steve’ DiNardo (left) and Gabriela ‘Gabby’ Vida (right) at Gabby's thesis defence
Stephen, what questions are your lab trying to answer?
SD: What drives us is how a niche influences its resident stem cells. Stem cells must self-renew, but they also must generate the appropriate amount of progeny, orient their divisions, cooperate with other stem cells, and respond to stresses within the tissue and organism. These myriad responses suggest not only that the cell biology of stem cells would be fascinating, but so would the cellular architecture of the niche that regulates those responses.
Gabriela, how did you come to work in the lab and what drives your research today?
GV: After my rotation in the lab, I knew this was where I wanted to do my thesis work. Steve is a one-of-a-kind mentor and extremely passionate about understanding why cells execute the behaviours necessary to promote the fidelity of a given tissue.
Tell us about the background of the field that inspired your work
SD & GV: Work from our lab showed that actomyosin contractility was required for the initial shaping of the niche. We then wondered whether this contractility was only required early, or if it might persist and also aid in later niche function. A peek into an RNAseq dataset suggested that the latter might be the case, and, indeed, our work showed that actomyosin contractility is also required for maintaining niche structure throughout adulthood.
Can you give us the key results of the paper in a paragraph?
SD & GV: Broadly, our key takeaways are that niche shape is required for proper stem cell behaviour. We found that the knockdown of Myosin II and its upstream regulator Rho Kinase disrupts niche shape. Those disruptions cause the germline stem cells (GSCs) to behave aberrantly. Notably, they respond less well to Jak/STAT signalling, an essential maintenance pathway for GSCs. Finally, they also execute misoriented divisions and bypass the GSC-specific centrosome orientation checkpoint.
When doing the research, did you have any particular result or eureka moment that has stuck with you?
GV: We have a pretty obvious niche structure defect, which was really exciting to see and gave me the sense that this was definitely going to lead us somewhere interesting. I think for me the most exciting part was looking at those defective niches using live-imaging. It was clear that there was something strange about them and, more surprisingly, I could see that there was also something wrong with stem cell behaviour.
A Myosin II 10 day knockdown niche. NicheGFP labels the niche in green; a germline cell boundary marker labels germ cells in magenta.
And what about the flipside: any moments of frustration or despair?
GV: The hardest part about this project was trying to understand mechanistically how the niche maintains its shape. We found that knockdown of Myosin II led to a reduction in localization of adhesion proteins at the niche-niche interfaces, but when we knocked down these adhesion proteins, we saw no change in niche shape. It is likely that the redundancy of adhesion molecules accounts for this lack of change, and this is still an active area of investigation.
Why did you choose to submit this paper to Development?
SD & GV: It is a premier journal for our field, ensuring that readers who wish to be aware of such results would see them.
Gabriela, what is next for you after this paper?
GV: I have recently wrapped up my time in the DiNardo lab and am now a post-doc in the Sivaramakrishnan lab where I am asking questions about transcription elongation in the developing C. elegans embryo.
And Stephen, where will this story take your lab next?
SD: There are a number of unanswered questions that may prove to be of general interest. How does the selective cytoskeletal polarity, which we find to be so important, arise within niche cells? What are the molecules and interactions within the niche cell cortex that influence the reading of a checkpoint within the stem cells?
Finally, let's move outside the lab – what do you like to do in your spare time?
GV: Steve and I both enjoy watching soccer, although our opinions on who should win major tournaments often differ. Steve is also gifted in ukulele playing, whereas my newest hobby has been crochet.
SD: Well, some of my ukulele partners may differ about the ‘gifted’ moniker! But, yeah, playing ukulele is my passion, of course!
Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, 421 Curie Blvd, Philadelphia, PA 19104, USA.
The Penn Institute for Regenerative Medicine, 421 Curie Blvd, Philadelphia, PA 19104, USA.
E-mail: [email protected]
