Migration and mechanical cross talk between tissues facilitates thorax closure in Drosophila

Work done in the lab of Prof. Pradip Sinha at BSBE, IIT Kanpur

About author

Thamarailingam did his Ph.D. from the Department of BSBE, IIT Kanpur and he is currently a post-doctoral fellow at the Mechanobiology Institute, National University of Singapore. During his Ph.D, he worked on tissue fusion processes during fly development, and Drosophila cancer and neurodegenerative models. His current work includes understanding morphogen gradient formation, and understanding heart development from the mesoderm of the Drosophila embryo.

Saurabh Singh Parihar did his Bachelor’s (B.Tech in Biotechnology) from Allahabad Agriculture Institute, Naini (currently known as SHUATS), and his Master’s (M.Tech) from the Department of Biological Sciences and Bioengineering, IIT Kanpur. He was also awarded a gold medal for his performance during his bachelor’s. He is currently pursuing his doctoral studies under the guidance of Prof. Pradip Sinha at the Department of Biological Sciences and Bioengineering, IIT Kanpur. His research mainly focuses on cytoskeletal remodeling during development and disease conditions. Additionally, he is also interested in studying tumor-host crosstalk and he aspires to pursue a career in investigating cytoskeletal dynamics in the field of cancer and other disease conditions.

Interview

How would you explain your research outcomes to the non-scientific community?

The emergence of adult structures during development sometimes involves the complex crosstalk among multiple tissues. For instance, during vertebrate craniofacial development, individually developed tissues stitch together to form an adult skull and palates. Failures in such tissue closure/fusion events during development lead to congenital birth defects such as spina bifida, and cleft palate defects. Model organisms such as mice and Drosophila have been utilized to explore the mechanisms of tissue fusion events during development and in adult life such as wound healing/closure.

In our study we investigated the mechanisms of a tissue fusion event, termed thorax closure, that takes place in Drosophila (commonly known as ‘fruit fly’) pupal stages. Metamorphosis in Drosophila pupa entails the death of larval tissues and replacement by adult tissues to form the final adult organs. During the development of an adult thorax, thorax closure occurs that involve the migration of two developing halves of the future thorax towards each other followed by their fusion. Our study for the first time showed that the dying larval epidermis that intervenes in the contralateral adult halves of the thorax assists the migration of the latter. We found that the ‘death-signal’ in the larval epidermis triggers a series of active contractions within the larval epidermis, and as a result, the entire tissue shrinks. Shrinkage of the larval epidermis brings the thoracic halves closer that reside above them, and both the tissues are connected by inter-tissue integrin adhesion. We believe that the contractile forces generated within the larval epidermis are relayed to the contralateral thoracic halves, pulling them towards the body midline and facilitating their fusion.

Cartoon representation of tissue closure event during Drosophila thorax development. The underlying larval epidermis, while undergoing degeneration (seen as delaminated yellow cells), provides an additional layer of forces (green arrow), besides thoracic epithelium-derived forces (red arrow), to pull the two contralateral halves of the thoracic epithelium towards the body midline. This entire event is crucial for the formation of a bilaterally symmetrical adult thorax.

How do these findings contribute to your research area?

Previous works on thorax closure focused on the autonomous role of thoracic tissues in their migration during thorax closure process. In particular, the role of the leading edges of the thoracic epithelia in their migration over the underlying larval epidermis is evident. However, the role played by the adjacent tissue, the larval epidermis in thorax closure, is unclear before, as the event occurs deep inside an opaque pupa. We took the work further and developed methods to image the pupa over the cuticle with the tissues expressing brighter fluorophores. Our study suggests that the contractile forces generated by the larval tissues are important too, besides the activity of the leading edges of the thoracic tissue. Our work along with the work done by previous researchers provides a holistic view on the mechanism of the thorax closure where both autonomous (leading edge centric) and non-autonomous (larval epidermal contraction) mechanisms act together to drive the migration of the thoracic epithelium. Therefore, in any tissue closure event during development or during the wound closure stage of the vertebrate wound healing, our work insists on looking out for non-autonomous cross-talk of the neighboring tissues besides the one which is migrating or healing, respectively.

Works on developmental tissue closure events always improve our understanding of adult wound healing, thus helping in their therapeutic intervention. For instance, developing targeted therapies to assist surrounding tissues in order to facilitate wound healing.

“the brainstorming sessions with our supervisor and inputs from our lab mates have always been exciting.”

What was the exciting moment during your research?

The whole journey in this project was exciting. Initially, we struggled a lot with developing a standard protocol for the live imaging of the thorax closure, as the entire process occurs inside a hard pupal case. Additionally, dissecting out the entire region was quite a challenging task and it took a lot of hits and trials to come up with a plan of our own. After these initial troubleshoots, it was a great journey and the publication proved cherry on the top. Furthermore, the brainstorming sessions with our supervisor and inputs from our lab mates have always been exciting.

What do you hope to do next?

With regards to the future of this project, we aim to dissect what triggers such a transformation in the larval epidermis. It is interesting to see that only the larval epidermis near the closure site undergoes degeneration, while the rest of the epidermis remains intact. Thus, it is likely that local signals from the thoracic epithelium could trigger such an event.

Additionally, it is possible that other tissues, besides the larval epidermis, could also contribute to the thorax closure. For instance, it will be interesting to explore any involvement of immune cells and muscle layers in this process which are present beneath the larval epidermis during thorax closure.

Where do you seek scientific inspiration from?

Saurabh: In my opinion, biology is the most fascinating field of science. The thing that fascinates most is there is no end to biological mysteries: every theory, every mechanism you read will have exceptions. My fascination became my passion during my post-graduation days at IIT Kanpur, where I got interested in mechanobiology and developmental biology.

Thamarai: I believe in curiosity driven research. This work was started when I first did time-lapse imaging of thorax closure in the pupa. What I observed is the larval epidermal tissue degenerates and at the same time, the adult thoracic epithelium migrates. Most of the projects I worked on are driven and based on the curiosity to know more about the initial observations.

How do you intend to help Indian science improve?

Saurabh: The bottleneck of Indian science is the lack of ‘originality’ and our need for constant approval from western countries. I think what our country needs is a ‘safe and trusted research niche’ which will encourage Indian researchers to work on core biology. Indian science could also gain a lot by developing ‘scientific platforms’ where scientists and scholars interact and discuss their successes and failures.

Thamarai: I am interested in understanding animal development using fruit fly development as a model. I have gained expertise in generating transgenic fly lines and analysing them using various microscopic techniques starting from confocal microscopy, lightsheet to single molecule spectroscopic techniques. In future, given a chance to pursue research in India, I will use all my abilities to generate disease models using fruit flies to understand disease progression and their therapeutic intervention.

Reference

Athilingam T, Parihar SS, Bhattacharya R, Rizvi MS, Kumar A, Sinha P. Proximate Larval Epidermal Cell Layer Generates Forces for Pupal Thorax Closure in Drosophila. Genetics. 2022 Feb 15:iyac030. doi: 10.1093/genetics/iyac030.

Edited by: Sukanya Madhwal

Meet the managers

Surabhi Sonam

Surabhi Sonam is an Assistant Professor. Along with teaching and research, she has a very strong interest in science communication. She has written several poems and blogs to communicate scientific principles and concepts. She is also volunteering with several science communication platforms as a content contributor and content editor. Under her supervision, her students have launched a scicomm magazine, Scinion which represents science in verbal and visual forms.

Sejal Dixit

Sejal Dixit is currently a 3rd-year student pursuing BSc triple majors in biotechnology, zoology, and chemistry from CHRIST (Deemed to be University). She loves to read, be it short stories, novels, magazines, or research articles. She is working with her college professor on a few papers, and wishes to pursue her master’s degree in stem cells and regenerative medicines. She has no problem socializing with new people and possesses leadership qualities. Her hobbies are dancing and traveling.

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