Publications
Shiroor DA, Wang KT, Sanketi BD, Tapper JK, and Adler CE. EMBO Reports, 24(5):e56112 (2023)
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The DNA damage response kinase ATM drives stem cell apoptosis in radiated planarians. Knockdown of atm prevents stem cell apoptosis after radiation and enables long‐term animal survival and regeneration through a reliance on homologous recombination.
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Planarian ATM enforces the G1/S checkpoint and drives radiation‐induced stem cell apoptosis independently of its canonical effector p53.
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Knockdown of atm results in atypical stem cell survival in planarians exposed to high doses of radiation.
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Stem cells in radiated atm knockdown animals rely on homologous recombination to resume cycling and fuel long‐term animal survival and regeneration.
Wendt G, Shiroor DA, Adler CE and Collins, JJ III. PNAS, 119 (37) e2205201119 (2022)
P53 is an important tumor suppressor that is found throughout metazoans, including invertebrates that do not develop malignancies. The prevailing theory for why these invertebrates possess a tumor suppressor is that P53 originally evolved to protect the germline of early metazoans from genotoxic stress such as ultraviolet radiation. Here, we examine the function of two P53 homologs in the parasitic flatworm Schistosoma mansoni. The first is orthologous to canonical P53 and regulates flatworm stem cell maintenance and differentiation. The second P53 gene is a parasite-specific paralog that is required for the normal response to genotoxic stress. The existence of this parasite-specific paralog implies that the ability to respond to genotoxic stress in parasitic flatworms may have arisen from convergent evolution.
Bohr TE, Shiroor DA, and Adler CE. eLife, 10:e68830. doi: 10.7554/eLife.68830 (2021)
In order to regenerate tissues successfully, stem cells must detect injuries and restore missing cell types through largely unknown mechanisms. Planarian flatworms have an extensive stem cell population responsible for regenerating any organ after amputation. Here, we compare planarian stem cell responses to different injuries by either amputation of a single organ, the pharynx, or removal of tissues from other organs by decapitation. We find that planarian stem cells adopt distinct behaviors depending on what tissue is missing to target progenitor and tissue production towards missing tissues. Loss of non-pharyngeal tissues only increases non-pharyngeal progenitors, while pharynx removal selectively triggers division and expansion of pharynx progenitors. By pharmacologically inhibiting either mitosis or activation of the MAP kinase ERK, we identify a narrow window of time during which stem cell division and ERK signaling produces pharynx progenitors necessary for regeneration. These results indicate that planarian stem cells can tailor their output to match the regenerative needs of the animal.
Shiroor DA, Bohr T, and Adler CE. Current Biology, 30(11):2166-2174 (2020)
Stem cells are continuously exposed to multiple stresses, including radiation and tissue injury. As central drivers of tissue repair and regeneration, it is necessary to understand how their behavior is influenced by these stressors. Planarians have an abundant population of stem cells that are rapidly eliminated after radiation exposure via apoptosis. Low doses of radiation eliminate the majority of these stem cells, allowing a few to remain [1]. Here, we combine radiation with injury to define how stem cells respond to tissue damage. We find that a variety of injuries induced within a defined window of time surrounding radiation cause stem cells to outlast those in uninjured animals. Injury stimulates localized cell death adjacent to wounds [2], in the same regions where stem cells persist. This persistence occurs in the absence of proliferation. Instead, stem cells are retained near the wound due to delayed apoptosis, which we quantify by combining fluorescence-activated cell sorting (FACS) with annexin V staining. Pharmacological inhibition of the mitogen-activated protein (MAP) kinase extracellular signal-regulated kinase (ERK) prevents stem cell persistence after injury, implicating wound-induced ERK activity in this response. By combining radiation with injury, our work reveals a novel connection between dying cells and stem cells that remain. Furthermore, the ability to induce stem cell persistence after radiation provides a paradigm to study mechanisms that may contribute to unanticipated consequences of injury, such as tumorigenesis.
Shiroor DA, Bohr T, and Adler CE. Journal of Visual Experiments, 133: e57168 (2018)
Planarians are flatworms that are extremely efficient at regeneration. They owe this ability to a large number of stem cells that can rapidly respond to any type of injury. Common injury models in these animals remove large amounts of tissue, which damages multiple organs. To overcome this broad tissue damage, we describe here a method to selectively remove a single organ, the pharynx, in the planarian Schmidtea mediterranea. We achieve this by soaking animals in a solution containing the cytochrome oxidase inhibitor sodium azide. Brief exposure to sodium azide causes extrusion of the pharynx from the animal, which we call "chemical amputation." Chemical amputation removes the entire pharynx, and generates a small wound where the pharynx attaches to the intestine. After extensive rinsing, all amputated animals regenerate a fully functional pharynx in approximately one week. Stem cells in the rest of the body drive regeneration of the new pharynx. Here, we provide a detailed protocol for chemical amputation, and describe both histological and behavioral methods to assess successful amputation and regeneration.
S.K. Bali, M.G. Garimella, D.A. Shiroor et. al; J Immunol (2016) 196 (12): 5024–5035 (2017)
Osteoarthritis (OA) is a chronic disease of articular joints that leads to degeneration of both cartilage and subchondral bone. These degenerative changes are further aggravated by proinflammatory cytokines including IL-1b and TNF-a. Previously, we have reported that IL-3, a cytokine secreted by activated T cells, protects cartilage and bone damage in murine models of inflammatory and rheumatoid arthritis. However, how IL-3 protects cartilage degeneration is not yet known. In this study, we investigated the role of IL-3 on cartilage degeneration under both in vitro and in vivo conditions. We found that both mouse and human chondrocytes show strong expression of IL-3R at gene and protein levels. IL-3 increases the expression of mouse chondrocyte-specific genes, Sox9 and collagen type IIa, which were downregulated by IL-1b. Moreover, IL-3 downregulated IL-1b– and TNF-a–induced expression of matrix metalloproteinases in both mouse and human chondrocytes. Interestingly, IL-3 reduces the degeneration of articular cartilage and subchondral bone microarchitecture in a mouse model of human OA. Moreover, IL-3 showed the preventive and therapeutic effects on cartilage degeneration induced by IL-1b in micromass pellet cultures of human mesenchymal stem cells. Thus, to our knowledge, we provide the first evidence that IL-3 has therapeutic potential in amelioration of degeneration of articular cartilage and subchondral bone microarchitecture associated with OA
