The people behind the papers – Tiffany Roach and Kari Lenhart

Kari Lenhart (left) and Tiffany Roach (right). Credit: Elizabeth Waldie.

Kari, what questions is your lab trying to answer?

KL: I am really fascinated by basic questions in developmental biology. How do cells influence each other? How are tissues maintained over time? What is the consequence to the tissue if cell interactions become disrupted? So my lab is focused on addressing these types of basic questions using the fruit fly testis as a model system. The direction of the lab right now is really taking what we've learned about the normal functioning of the system and using that to understand what goes wrong under disease or stressful conditions.

Tiffany, how did you come to work in Kari's lab and what drives your research today?

TR: After completing my first two rotations in person, I did my third rotation entirely virtually with Kari during the COVID shutdown. Together, we enjoyed many Zoom meetings, discussing papers, data and experiments – with an occasional interruption by Kari's (at the time) 2- and 5-year-old children. Despite not conducting a single experiment in her lab, I simply fell in love with her enthusiasm for science, which turns out to be infectious, and the rest is history.

What was known about how ‘stress’ phenomena affects the male germline stem cell niche before your work?

TR & KL: Before live imaging, much of how stress impacted the testis stem cell niche was determined by end-point analyses such as quantification of stem cell numbers and progeny, as well as overall organization and morphology of the cells. For example, aging and nutrient deprivation can lead to tumor formation, as indicated by the accumulation of undifferentiated germ cells that are no longer interconnected outside of the niche. However, where they originated and how they abscise from one another remains elusive. Through direct visualization of these cells over time, we can observe how cellular dynamics such as cytokinesis timing, cell migration and cell-cell interactions become disrupted with stress. Current work in our lab uses live imaging combined with powerful genetic tools to study tumor initiation to further characterize ‘stem-like’ tumors and the mechanisms underlying tumorigenesis.

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

TR & KL: We find that mating induces increased ecdysone signaling in testis soma, which disrupts somatic encystment of the germline. As a consequence, defective encystment causes abscission failure in germline stem cells, which prevents release of differentiating daughter cells. We also show that this effect is transient and depends on active mating stress; with continued intermittent mating stress, decreased encystment of germ cells may allow those germ cells to move back to the niche to preserve the stem cell pool.

Were you surprised that exposure to ecdysone was sufficient to cause the abscission defect in the absence of mating?

TR: Pleasantly surprised, yes! Often there are multiple pathways working in tandem to elicit tissue-wide responses. So even though we knew it was an essential experiment, we really weren't expecting to get a positive result.

KL: That was a very exciting day in the lab when Tiffany shared those results with me.

How do you think mating stress affects the stem cell niche in other systems?

TR: In multiple organisms, mating shortens lifespan. This is largely due to the fact that the germline is energetically costly and, therefore, fewer nutrients are allocated to somatic tissues. So, I would suspect that other stem cell niches are less productive and have shorter longevity under continuous mating conditions.

KL: One of my main goals for the future of the lab is to collaborate with scientists working in different organisms to study whether any of the complex cell interactions we're identifying in the fly testis between soma and germline are conserved in other species. It seems very likely, given the similarities between the fly and mammalian testes. It would be really exciting to analyze germline stem cell divisions and cytokinesis in, say, a zebrafish to study normal tissue function and then what effect mating has on the system.

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

TR: We have always thought that an important step in germ cell de-differentiation is to break contact with surrounding soma. However, this has not been directly studied. Therefore, it was especially exciting for us to observe germ cell de-differentiation in a context where we quantitatively show somatic encystment is disrupted, as this would explain how disrupting soma-germline interactions can serve an adaptive function despite its temporary effect on germ stem cell cytokinesis.

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

TR: As I had never conducted optogenetic experiments before this work, I had to learn about the methodology and modify previous protocols to a simple setup for what we needed. My first attempts at stimulating the flies with red light were unsuccessful. Then, I learned that anesthetizing the flies on CO₂ was preventing the behavior! A comically simple fix to anesthetizing the flies on ice did the trick and you can imagine both the excitement and horror I felt as I watched the fly ejaculate into solution under the stereoscope.

Tiffany, what is next for you after this paper?

TR: Using what I learned from mating and its effects on somatic encystment, I am now looking directly at the somatic cells to characterize their behaviors under normal and stress conditions.

Kari, where will this story take your lab next?

KL: Tiffany's beautiful work and other exciting data that's still unpublished from our lab really suggests that maintenance of homeostasis requires a tight balancing act. There's a need for plasticity in the system so stem cells can be replaced if lost, but it's clear that any misregulation of that plasticity very quickly turns into tumorigenesis. I'm excited to keep studying the effects of stress on the tissue and to really delve into the idea that the same behaviors we think are adaptive under stress (such as decreased soma-germline contacts and de-differentiation) are exactly the same behaviors that contribute to disease and loss of homeostasis if misregulated.

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

KL: I love gardening and walking in the woods behind my house with my family.

TR: In my spare time I love to garden, watch movies and play frisbee with my dog, Zelda!