The people behind the papers – Jae-In Lee, Sumin Park and Kwang-Min Choe

From left to right: Sumin Park (co-first author), Kwang-Min Choe (corresponding author) and Jae-In Lee (co-first author)

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

K-MC: We have been studying how cells respond to stress, such as wounding or tissue degeneration, using Drosophila as a model. While much is known about how the immune system detects pathogens, it remains unclear how it distinguishes between damaged self-tissues and healthy ones. We conducted a genetic screen to identify key players in this process, and along the way, we unexpectedly came across Papilin. In this paper, we explored how Papilin functions in blood cell development, as part of the extracellular matrices (ECMs) in the lymph gland. Interestingly, we found that Papilin regulates haematopoiesis by influencing other matrix proteins and regulating intracellular signalling.

Jae-In and Sumin, how did you come to work in the lab and what drives your research today?

J-IL & SP: During our undergraduate years, we had the opportunity to take Professor Choe's developmental biology course, which sparked our fascination with the field. His lectures emphasised that, while developmental biology is fundamental, many questions remain unanswered. More importantly, we realised that exploring these questions deepens our understanding of development and provides insights into disease mechanisms. This naturally led us to join his lab, where Professor Choe valued our ideas and instilled the right mindset for approaching science. As early-career researchers, his guidance was key to our growth as scientists. The experience of learning from him and conducting research remains irreplaceable. We continue to focus on developmental biology, especially stem cell diversity.

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

K-MC: I am deeply grateful to the researchers who laid the foundational work for this field. To list just a few: Jung et al. (2005) from the Banerjee group for their comprehensive work on lymph gland development; Grigorian et al. (2013) from the Hartenstein group for investigating the role of the lymph gland matrix protein Trol; Kramerova et al. (2000) from the Fessler group for the isolation and characterisation of Papilin; and Pastor-Pareja (2020) for his excellent work on extracellular matrices. I also appreciate the pioneering and inspiring contributions of Tahir and Rose Rizki in the study of insect blood cells. Additionally, I'd like to thank von Bredow for generously sharing Fessler's Papilin antisera, and H. Gook, my former student, for her collaborative role in establishing the lymph gland analysis in my lab.

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

J-IL & SP: Our study reveals the crucial role of the matrix glycoprotein Papilin in the Drosophila lymph gland. Papilin, which is primarily synthesised by plasmatocytes, forms lamellae in the medullary zone where prohaemocytes reside. Upon microbial infection or wasp infestation, these lamellae collapse, which is accompanied by enhanced haemocyte differentiation. These findings suggest that Papilin plays a key role in maintaining prohaemocyte populations and regulating differentiation under physiological conditions. We also found that Papilin colocalises with key ECM components, including collagen, laminin, nidogen and perlecan. Loss of Papilin disrupted ECM organisation, notably affecting perlecan. These results indicate that Papilin interacts with other ECM proteins to regulate tissue homeostasis. Notably, phenotypes caused by Papilin depletion could be partially rescued by perlecan overexpression or EGFR pathway inhibition, highlighting the interplay between ECM integrity and signalling in haematopoiesis. These findings underscore the essential role of ECM components in lymph gland architecture, and suggest that Papilin regulates haematopoietic homeostasis in response to developmental and environmental cues.

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

J-IL & SP: A memorable result from our study was that knocking down Papilin using fat body-specific GAL4 did not reduce the protein level in the fat body, despite previous research suggesting that the fat body, together with haemocytes, are the primary sources of Papilin. With haemocyte-specific GAL4, however, we observed a decrease in Papilin levels in both the lymph gland and the fat body. This led to the exciting realisation that haemocytes are the major source of Papilin in both tissues. Additionally, while screening signalling pathways to explore the molecular mechanism of Papilin, we had a breakthrough when we knocked down EGFR-related molecules. We used the inducible and ubiquitous hsp70-GAL4 driver for efficient screening, and then focused on specific lymph gland zones with zone-specific GAL4 drivers. These experiments revealed that EGFR signalling in the medullary zone (MZ) affects progenitor maintenance and differentiation. At the same time, access to relevant papers from Jiwon Shim's lab reinforced our findings. This was particularly thrilling, as it felt as though we had finally made a significant step closer to understanding the mechanism after a long and challenging effort.

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

J-IL & SP: Visualising Papilin was a significant challenge. We struggled with various difficulties, beyond generating antisera, in an attempt to create GFP-tagged Papilin fly lines. Immunohistochemistry posed another obstacle. Conventional methods did not provide us with the lamellae or septa we expect to see, as other ECM proteins do. Staining patterns varied drastically, complicating interpretation. After testing multiple protocols systematically, we were able to produce high-quality images of Papilin with reproducibility, primarily with help from Sharma et al. (2019), whose method involves antisera incubation before fixation.

Jae-In and Sumin, what is next for you after this paper?

SP: I am now preparing to move on to a new environment and begin the next phase of my research. I find myself particularly drawn to inter-organ crosstalk – an aspect briefly touched upon in our study. Exploring how organs communicate at a deeper level fascinates me, and I look forward to investigating this further. With the knowledge and research mindset I gained from the current lab, I am eager to embrace new challenges, expand my scientific expertise and apply the lessons I've learned as I progress in my scientific journey.

J-IL: My research has given me a strong foundation in developmental haematopoiesis and ECM biology, particularly in how ECM components regulate blood cells. Now, I aim to apply this expertise in the pharmaceutical industry to develop innovative solutions for unmet medical needs. I am especially interested in ECM biology, cell signalling and genetic manipulation techniques to advance drug discovery and development. The opportunity to translate scientific discoveries into life-changing therapies excites me, and I am exploring roles in biotech and pharmaceutical companies focused on regenerative medicine and ECM-targeted therapies.

Kwang-Min, where will this story take your lab next?

An improved way of Papilin visualisation will help better understand its molecular function, including its turnover and interaction with other ECM molecules in development and disease conditions. We are also interested in Papilin's role in the periphery, as alluded to above. Kramerova et al. (2000) noted that Papilin and other ECM molecules are strongly secreted by freshly collected haemocytes upon encountering foreign surfaces. Rizki and Rizki (1980) proposed, based on heterospecific implantation experiments, that the greater the difference in surface properties, the higher the likelihood of melanotic encapsulation on foreign tissues. Combined with the melanotic mass phenotype observed in Papilin-knockdown larvae, these results raise the intriguing possibility that Papilin may be involved in the self-tissue identification process. We are eager to explore this further.

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

SP: I spend a lot of time discussing ideas with my lab mates, but outside the lab, I love catching up with friends over good food and a nice cup of coffee. Engaging in conversations, whether in the lab or at a cozy café, helps me unwind and recharge. I also enjoy travelling to new places and embracing the feeling of being a stranger in unfamiliar settings. There is something exhilarating about exploring places I've never been before, immersing myself in different cultures and experiencing the unexpected.

J-IL: Long hours in the lab often lead to neck, shoulder and back pain, so I made it a habit to exercise before heading in. It helps me feel both physically and mentally refreshed. I've always enjoyed swimming and did it regularly, and during my PhD, I also started learning to play golf. More recently, I've gotten into CrossFit and I enjoy recommending it to my colleagues – it's been a great way to stay active and challenge myself.