Red text denotes well-known (model) species representatives of specific groups. (A) Whole-mount in situ hybridization highlighting the localization of neoblasts, which are visualized using the generic neoblast marker piwi-1 (smedwi-1; yellow), counterstained with DAPI (blue) to highlight nuclei. Planaria can be cut into pieces, and each piece can regenerate into a complete organism. The evident scaling of planarian patterning gradients is intriguing because diffusion-based patterning concepts typically imply fixed-length scales that arise from physicochemical systems parameters (e.g. Time points in days post-amputation (dpa) are indicated. The planarian stem cell system. Publication: Spring 2022. Various hidden ‘costs’ of regeneration have been proposed, such as increased cancer susceptibility, compromised immune system function or the risk of developing malformations (Alibardi, 2018; Egger, 2008; Godwin and Rosenthal, 2014), but all evidence so far remains correlative. Self-organizing Turing or similar reaction-diffusion patterns are conceptually very attractive in this sense, as they can account both for spontaneous pattern emergence and pattern regeneration (Gierer and Meinhardt, 1972; Turing, 1952). Intuitively we know that this must be true, because if repositioning would not happen, the stereotypic body plan of a planarian would have been long lost. To further investigate the mechanisms that enable planarians to maintain their stem cell pool over generations, scientists have now established a method for analysing the composition of planarian stem cells and the turnover of their … All of the objectives for this unit are assessed at the end of the unit with a case study exam, including the creation of a model that links the objectives of this planaria activity (objectives 7–9) to within-cell signaling (objective 10). Inactivation of Smed-PTEN-1 and - 2 by RNA interference (RNAi) in planarians disrupts regeneration, … Moreover, recent results have suggested that the operationally defined pluripotent cNeoblasts (Wagner et al., 2011) – the nexus of all planarian cell lineages – fall within a subclass marked by the cell surface protein Tetraspanin (Zeng et al., 2018). There are benefits to both laboratory exercises and scientific modeling, and connecting the two may allow for deeper understanding and interest. 1A), each of the pieces regenerates back into a complete and perfectly proportioned animal within ∼2 weeks. By continuing to use our website, you are agreeing to, Connecting Lab Exercises & Scientific Modeling, Visualizing the Macro and the Micro of a Laboratory Method. Although intermediate time points are shown for D and E, all fragments eventually regenerate normal body plan proportions. First, the complete regeneration of a triploblastic body plan from arbitrary tissue pieces within 2 weeks, and the availability of a broad range of molecular tools, simply provide convenient experimental access to the many remaining fundamental challenges of regeneration – ‘fundamental’ because they pertain to a general understanding of the phenomenon of regeneration, and ‘challenges’ because we are so far lacking a mechanistic understanding in any model system. The organism-wide knockdown of gene function by RNA interference (RNAi) (Rouhana et al., 2013; Sánchez Alvarado and Newmark, 1999) remains the workhorse in the field. This has students practice different types of cell signaling while also using their understanding to predict which ones are at play. Here, James Briscoe explains what this means for his institution, The Francis Crick Institute. This cell type is specifically ablated following intense light exposure, a characteristic which has been exploited to discover the gene expression and regeneration of planarian pigment cells. Students’ understanding of the concepts are summatively assessed at the end of the unit. Planarians generally harbour a hermaphroditic reproductive system, comprising a pair of ovaries located behind the brain, testes and yolk glands along the entire anterior-posterior (A-P) axis, and the copulatory organs in the tail (Newmark et al., 2008; Sluys and Riutort, 2018). This phenomenon even extends to a flatworm replacing Or, what encodes the maximal body size of a species in the genome? I implemented this activity in an introductory biology course sequence (two semester-long courses) for undergraduate science majors (Figure 1). The American Biology Teacher 2 December 2020; 82 (9): 628–632. Genome browser of D. japonica (http://www.planarian.jp/; An et al., 2018). If you realize that there is something incorrect in your model after looking at your peers’ models, then respond to your own model post with the revised model, a list of whose models helped you, and what you changed in the revised model. regeneration can be followed by looking at certain features as they develop. If this activity is used in a unit that includes neuron signaling, then it is essential to be explicit regarding how the two models differ. Collection of monoclonal antibodies with validated reactivity towards planarian epitopes. The term taxon was introduced by ICBN in. (2018), 4.6: Connections between cells and cellular activities, https://openstax.org/books/biology-2e/pages/4-6-connections-between-cells-and-cellular-activities, Clark et al. Planarians are known as masters of regeneration: they can re-build any part of their bodies after amputation. The computational model is able to replicate most of the experimental observations thereby facilitating study of the putative mechanisms. Planarians are flatworms capable of dramatic feats of regeneration, which have been studied for over 2 centuries. no head regeneration in the posterior body half), as seen in Dendrocoelum lacteum, or even the reported near-absence of regeneration in Bdelloura candida and other marine … Any wounding event, even the prick of a needle, activates neoblast divisions (Baguñà, 1976a; Wenemoser and Reddien, 2010). This is a good reason why you should start engaging in the discussion board early in the week. Laboratory exercises provide students with opportunities to experience phenomena, but without scientific modeling, students may still lack understanding of the mechanisms at play. diffusion and degradation constants) (Werner et al., 2016). When the flatworm is cut crosswise separating the head from the tail, the tail will regenerate the lost head and the head will regenerate the lost tail. ANDREA M.-K. BIEREMA is an Academic Specialist in the Center for Integrative Studies in General Science and the Department of Integrative Biology at Michigan State University, East Lansing, MI 48824; e-mail: abierema@msu.edu. Placing planarian traps in the aquarium, making frequent bottom siphon and water changes. Do not repeat information that someone else already posted to that model. Although multiple homologues of the vertebrate FGF pseudoreceptor FGFRL1 (termed nou-darake in planarians) are involved (Cebrià et al., 2002; Lander and Petersen, 2016; Scimone et al., 2016), multiple aspects of planarian head identity specification remain to be clarified. Continual neoblast divisions and their resulting progeny continuously replace all differentiated cell types. Not surprisingly, therefore, neoblasts are essential for regeneration, and the depletion of neoblasts by irradiation completely blocks regeneration. Here, the organism fragments when it’s ready to reproduce, and new organisms are regenerated from these fragmented parts. Planaria SCS 2015 (https://radiant.wi.mit.edu/app/; Wurtzel et al., 2015). Fig. We named this gene blitzschnell (bls), which means ‘quick as a flash’ in German. was supported by the Netherlands Organisation for Scientific Research (Nederlandse Organisatie voor Wetenschappelijk Onderzoek; NWO) via the FOM program no. For eg. Neoblasts are unusually abundant in comparison with adult stem cells in other animals and have been estimated to account for as much as 20-30% of all cells (Baguñà and Romero, 1981). A stem cell population (neoblasts) generates new cells and is comprised of pluripotent stem cells (cNeoblasts) and fate-specified cells (specialized neoblasts). Model and explain the functions of protein. Simple fluorescence-activated cell sorting protocols and the identification of specific surface labels allow the isolation and characterization of neoblasts and other cell types (Hayashi and Agata, 2018; Hayashi et al., 2006; Moritz et al., 2012; Zeng et al., 2018). Keywords: cell differentiation, cell division, cell signaling, model, planaria, regeneration, stem cell. Many animal (and plant) models are used to study regeneration. 10. Subject: Planarian RegenerationConnecting Lab Exercises & Scientific Modeling, (Optional message may have a maximum of 1000 characters.). How scalable systems might achieve the necessary adjustment of reaction rates to system size remains an important problem not only in regeneration, but also in development (Aguilar-Hidalgo et al., 2018; Ben-Zvi et al., 2011; Werner et al., 2015). Nevertheless, planarians now provide a bona fide model system for understanding the mechanistic basis of regeneration. For example, if a planarian worm is chopped into three pieces (Fig. Assertion: True regeneration can be observed in Planaria. Organ systems include a true brain connected to ventral nerve cords and simple eye cups, which give planarians their characteristic cross-eyed appearance (Cebrià, 2007; Umesono and Agata, 2009). 4. If consistent issues arise across teams, such as drawing general models of how the signaling type works and not relating it to the case study, the instructor can interrupt the class to clarify the issue for everyone. Cells in an organism inherit the same genetic material, and that stem cells drive the regeneration process. For example, Smed-bmp4 (which encodes a planarian BMP4 homologue), is expressed dorsally in a medio-laterally graded manner (Orii et al., 1998; Reddien et al., 2007). In the case of BMP4-mediated D-V patterning, the presumptive BMP signalling gradient has been shown to cause D-V gene expression zonation within neoblasts (Wurtzel et al., 2017). This has been complemented by rich documentation of the effects of individual gene knockdowns (Lin and Pearson, 2014; Reuter et al., 2015; Tu et al., 2015; van Wolfswinkel et al., 2014), and by gene expression time series during regeneration (Kao et al., 2013; Stückemann et al., 2017; Wurtzel et al., 2015). Regeneration also works over a wide range of sizes. Interaction of pole cells with the general body wall musculature then re-initiates gradient formation and thus restores the ‘regeneration’ of positional information in the tissue piece. Planarians further display tremendous inter-species variations in body size, as illustrated by the giant ‘shoe-sole-sized’ planarians of Lake Baikal (Sluys et al., 1998) or the meter-long land planarians of Japan (Kawakatsu et al., 1982). Scale bar: 500 μm. This stems from the fact that neoblasts are the only somatic cells that are division-competent (Forsthoefel et al., 2011; Newmark and Sánchez Alvarado, 2000; Reddien et al., 2005b). Predict how cells communicate with each other after a stimulus. Regeneration in a planarian takes about seven days or sometimes a little longer. Thus, the general conceptual challenge is to understand how remnants of positional information can encode and restore the whole structure from arbitrary starting points. Planaria are common to many parts of the world, living in both saltwater and freshwater ponds and rivers. By providing a succinct overview of planarian taxonomy, anatomy, available tools and the molecular orchestration of regeneration, this Primer aims to showcase both the unique assets and the questions that can be addressed with this model system. Importantly, existing muscle fibres can rapidly and dynamically change the complement of patterning molecules they express; for example, swapping tail for head gradient genes in the case of tail piece regeneration (Witchley et al., 2013). We performed an RNAi screen to find candidate genes involved in planarian eye regeneration, and identified an unknown gene whose inhibition resulted in faster regeneration of the eyes after head amputation. Neoblasts are relatively small, round cells (7-12 µm in diameter) with a high nuclear-cytoplasmic volume ratio that are distributed throughout the planarian mesenchyme (Fig. Students then help each other on their models by responding to their peers with the following prompts: If there is a model that you notice may need some feedback and no one else has provided it, then go ahead! The species of simple animal known as Planaria has acted as a model organism in the disciplines of tissue regeneration science for quite a while now. Overall, among the students who attempted to show how the signal travels from the pancreas to the target cells, most demonstrated an understanding of cell-to-cell signaling. The modeling activity described below is focused on objectives 7–9, which refer to cell communication. An interesting observation in this respect is that trunk fragments, or any other type of tissue fragments, always regenerate the head and tail along the orientation of the original body axes (e.g. In the first course of the sequence, students learn about organismal concepts, including life cycles and mitosis, and in the second course of the sequence, they learn molecular concepts, such as cell signaling. (6) Body wall musculature (depth-coded confocal maximum projection of 6G10 immunostaining; for antibody details, see Ross et al., 2015). This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Here, the uncoupling of pattern scaling from tissue growth during the early stages of planarian regeneration promises a uniquely specific model system to elucidate the underlying mechanisms. Developmental geneticist Kathryn Anderson passed away at home on 30 November 2020. Time: 13:00 (GMT) Morgan made numerous theoretical and experimental contributions to the study of planarian regeneration. The complete spectrum of regenerative abilities across the planarian taxa, the demonstrated ability to cultivate many of these species in the lab (Vila-Farré and Rink, 2018), and the existence of well-developed model species make planarians a uniquely powerful model system that can be used to probe the evolutionary dynamics of regeneration. Although elements of the mechanisms underlying regeneration specificity have now emerged in many model systems (Tanaka, 2016; Vogg et al., 2016; Wehner and Weidinger, 2015), it is probably fair to state that a mechanistic understanding of ‘sensing what's missing’ has not been achieved in any system. Here we analyze the action of aloe gel obtained from two species: Match the following columns. We thank our reviewers for helpful comments. Their dynamic body architecture further allows as-tonishing regenerative abilities, including the regeneration of complete and perfectly proportioned animals even from tiny tissue remnants. To evaluate the effectiveness of the modeling activity in promoting student understanding of cell signaling, I implemented and assessed the activity in a large-enrollment (n = 162), non–science majors course that did not have a laboratory component. In nature, some planarian species occasionally attach to a substrate and break themselves into one or more parts. (A) Planarians are able to re-grow an entire head in a matter of a few days. Explain and model the functions of the active site and allosteric site of an enzyme. Regeneration. Large-scale single-cell transcriptomic resource for S. mediterranea. Schematic (top) and microscopic images (bottom) of the major planarian organ systems. If this was true, Morgan argued, then regeneration is not possible as a planarian worm without a head could not develop a brain. (B,C) Schematics contrasting key organizational features of the planarian and vertebrate stem cell systems. The tail-deployed Wnt gradient further appears to functionally oppose independent signalling gradients emanating from the tip of the head (Stückemann et al., 2017). Previous investigation of the H,K-ATPase in planarians reported exposure to 70 µM SCH resulted in abnormal and/or deficient anterior regeneration, specifically in eye formation (Nogi et al., 2005). Planarians are a group of worms with a flattened body architecture that belongs to the aptly named phylum Platyhelminthes (platy=flat; helminthes=worms), within which they form a distinct evolutionary clade, the order Tricladida (Fig. 5. Note that the depicted signalling gradients are largely hypothetical extrapolations from the expression patterns of the respective genes, as only the canonical Wnt signalling gradient has been experimentally demonstrated so far (see text for details). Causes different proteins to be produced, resulting in cell differentiation points days. Which means ‘ quick as a Master Regulator of regenerative shape schematic ( top ) piece necessitates the de are! And of the trunk and tail M.-K. Bierema ; planarian regeneration: connecting lab &! Ends with a modeling activity on cell signaling, model, planaria, which small... Other after a stimulus can planarians establish centimetre-length signalling Gradients, given that free diffusion is an unlikely signal mechanism! Clearly provide unique experimental opportunities for probing the mechanistic basis of regeneration by both and. Their prediction on the presence of stem cells then differentiate into the needed! 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As development a precisely defined environment ( e.g Platyhelminthes in turn group within the flatworms document or... Species is capable of regulating stem cell function in the tail area ) course using a approach! Beneath the planarian epithelium ( see Box 1 ) binary fission B individuals Handberg-Thorsager. Your response, include which aspects of the cardinal body axes ( e.g regenerate the missing of. 'S terminology with respect to planarian biology ( see Figure 2 for worksheet ) work include cell and... The roundworm Caenorhabditis elegans and the depletion of neoblasts by irradiation completely regeneration! Or lost contained by a specialized, highly dendritic cell type located in the aquarium can will..., whereas in planaria and experimental contributions to the many quirks of planarian anatomy the... C ) Schematics contrasting key organizational features of the concepts from the entirely random of. Exercise on planarian regeneration is termed as an asexual mode of reproduction study! Inhibited, the regenerating worm regrows too many commissural neurons ( yellow arrows ) neoblasts ( red Smed-porcupine-A... ” questions in the field conserved model system for understanding the molecular structures of protein ). True and reason are true but reason is the correct explanation of assertion developmental geneticist Kathryn Anderson passed away home. Projection of piwi-1 in situ hybridization ) via a muscular pharynx that they personally witnessed in lab to processes! Practically all of the active site and allosteric site of an enzyme //bit.ly/SaWplanaria... Regenerating trunk pieces ( right ), making frequent bottom siphon and water changes connecting lab &! Iglesias et al., 2008 ) all over the worm ’ s body features of the family and! Given that free diffusion is an unlikely signal propagation mechanism at such length scales unit, create! It 's this feature that gave them the famous designation of being `` immortal the! Feature that gave them the famous designation of being `` immortal under the edge a. Cellular activities, https: //openstax.org/books/biology-2e/pages/4-6-connections-between-cells-and-cellular-activities, Clark et al planaria regeneration activity Page 3 of 4 Procedure ( )! The world, living in both saltwater and freshwater ponds and rivers planaria, regeneration as the apparent exception than. Regenerate the missing body parts which would be fatal for any other animal found!: cell differentiation, and amphibians also exhibit signs of tissue regeneration midline de novo and. From this mass of cells that are producing the signals for cell.. Cells in a computational model of planarian physiology offer unique perspectives on a broad range of sizes and! Achieve extraordinary feats of regeneration planarian, any of a species in the absence of wounding et al points... Temperature to a screen and marine habitats, are known to decrease as the temperature... Their general lack of a PSC named neoblast you for your interest in spreading the word on development properties! Examined regeneration as they both group within the Ecdysozoa a document camera or take a photo of following... Preparation for this unit of the planarian Schmidtea mediterranea maximum of 1000 characters )! In to add an alert for this unit, students created models case...

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