Kenneth D. Poss, Ph.D. (Massachusetts Institute of Technology)
How and why tissue regeneration does (or does not) occur are critical questions. The biology of regeneration remains both challenging and fascinating, and new discoveries have the potential to impact clinical outcomes of many diseases of organ damage, including heart failure, Alzheimer's disease, and diabetes.
It has been known for centuries that salamanders and fish regenerate complex tissues much more effectively than mammals. Zebrafish have emerged as a central model system for studying regeneration, due to their ability to regenerate myriad tissues and to the availability of molecular genetic tools. Over the past decade, our laboratory has spearheaded the use of zebrafish to reveal concepts and mechanisms of regeneration.
We study the initial morphogenesis and injury-induced regeneration of several tissues in zebrafish. Our student and postdoc projects investigate adult hearts, fins, spinal cord, skin, scales, and other tissues. We have also begun to test ideas in mammalian models.
There is little natural regeneration of the major structural cells of the adult mammalian heart, the cardiomyocytes, after injury. This regenerative shortcoming is highly relevant to human disease, given the high prevalence in the United States of ischemic myocardial infarction and heart failure. Many years ago, we introduced a model system approach to heart regeneration, by showing that adult zebrafish can regenerate new muscle lost after major cardiac injury. Since then, we have found that cardiac regeneration is not based on stem cells, but rather involves activation and proliferation of spared cardiac myocytes. We also have demonstrated multiple roles during heart regeneration for the epicardium, a thin epithelial layer enveloping the cardiac chambers, and the inner endothelial lining of the chambers called the endocardium. Together, models like zebrafish and neonatal mice have great potential to reveal methods to gauge and stimulate human heart regeneration. We are continuing to investigate how muscle and non-muscle cells respond to injury and orchestrate regeneration. Key issues include the identification of cardiomyocyte mitogens, the definition of gene regulatory elements that activate regeneration programs, and how to use fundamental mechanistic data in platforms to boost cardiac regenerative capacity in mammals. Our methods are exploratory and rely heavily on generation of new mutant and transgenic animals.
Zebrafish fins are transparent, intricately patterned structures, making them tractable for asking fundamental questions about complex tissue regeneration. Within two weeks after amputation of a fin, a series of healing, proliferation, and patterning events replaces bone, epidermis, blood vessels, nerves, and connective tissue mesenchyme. Our work on fin regeneration has helped establish the cellular origins of regenerated fin tissue, and it has identified new concepts and molecular mechanisms of appendage regeneration. We are pursuing informative mutants in fin regeneration, both by forward genetic screens and targeted gene editing. Also, we are developing new methods for imaging of key cellular and molecular events during regeneration, to acquire and quantify live cellular and subcellular events in regenerating complex tissues.
Spinal Cord Regeneration
The path to an effective regenerative therapy for spinal cord injury requires a combination of molecular, cellular, electrostimulatory, and engineering approaches, and can be guided by a deeper understanding of the inherent regenerative capacity of spinal cord tissue. Remarkably, only a handful of groups worldwide use adult zebrafish to investigate the innate ability for spinal regeneration. Just 6 to 8 weeks after a paralyzing injury that completing severs their spinal cord, zebrafish form new neurons, regrow axons, and recover the ability to swim. Importantly, these regenerative events proceed without massive scarring. Instead, following injury, specialized glial cells assist in forming a tissue bridge over the two severed ends, allowing axons to grow across the wound and reestablish crucial connections. We are exploring the underlying gene regulatory mechanisms of spinal cord regeneration, with the goals of finding key factors and regulatory sequences that initiate regeneration programs in spinal cord cell types.
Cao, J., Wang, J., Jackman, C. P., Cox, A., Trembley, M. A.Balowski, J. J., Cox, B. D., Dickson, A. L., Di Talia, S., Bursac, N., Small, E. M., and Poss, K. D. (2017). Tension creates an endoreplication wavefront that leads regeneration of epicardial tissue. Developmental Cell 42, 600-615.
Chen, C. H. and Poss, K. D. (2017). Regeneration genetics. Annual Review of Genetics 51, 63-82.
Tzahor, E. and Poss, K. D. (2017). Cardiac regeneration strategies: Staying young at heart. Science 356, 1035-1039.
Tornini, V. A., Thompson, J. D., Allen, R. L., and Poss, K. D. (2017). Live fate-mapping of joint-associated fibroblasts visualizes expansion of cell contributions during zebrafish fin regeneration. Development 144, 2889-2895.
Goldman JA, Kuzu G, Lee N, Karasik J, Gemberling M, Foglia MJ, Karra R, Dickson AL, Sun F, Tolstorukov MY, Poss KD. (2017). Resolving Heart Regeneration by Replacement Histone Profiling. Dev Cell. 27;40(4):392-404.e5.
Karra R, Poss KD. (2017). Redirecting cardiac growth mechanisms for therapeutic regeneration. J Clin Invest. 1;127(2):427-436.
Tornini VA, Puliafito A, Slota LA, Thompson JD, Nachtrab G, Kaushik AL, Kapsimali M, Primo L, Di Talia S, Poss KD. (2016). Live Monitoring of Blastemal Cell Contributions during Appendage Regeneration. Curr Biol. 21;26(22):2981-2991.
Mokalled MH, Patra C, Dickson AL, Endo T, Stainier DY, Poss KD. (2016). Injury-induced ctgfa directs glial bridging and spinal cord regeneration in zebrafish. Science. 4;354(6312):630-634.
Di Talia S, Poss KD. (2016). Monitoring Tissue Regeneration at Single-Cell Resolution. Cell Stem Cell. 6;19(4):428-431.
Wang J, Poss KD. (2016). Methodologies for Inducing Cardiac Injury and Assaying Regeneration in Adult Zebrafish. Methods Mol Biol. 1451:225-35.
Cao J, Poss KD. (2016). Explant culture of adult zebrafish hearts for epicardial regeneration studies. Nat Protoc. 11(5):872-81.
Kang J, Hu J, Karra R, Dickson AL, Tornini VA, Nachtrab G, Gemberling M, Goldman JA, Black BL, Poss KD. (2016). Modulation of tissue repair by regeneration enhancer elements. Nature. 14;532(7598):201-6.