Freshwater planarians have a complex body-wall musculature that functions mainly as a skeletal support and during locomotion. In addition, the digestive system consists of a highly muscular tubular organ, the pharynx, and a highly ramified gut surrounded by enteric musculature that mediates peristaltic movements during food intake and digestion.
At the gene expression level the 2 muscle types express distinct forms of myosin heavy-chain genes. Planarians can regenerate and renew any type of cell and tissue through the differentiation of neoblasts, a population of adult pluripotent stem cells.
These animals thus constitute an ideal model for the in vivo study of how these stem cells become committed and differentiate into the muscle lineage during regeneration.
Preliminary results suggest that neoblasts become committed to the myogenic lineage before they enter the regenerative blastema, supporting the recently proposed existence of specialized neoblasts.
However, definitive experimental proof is required, preferably obtained by studying the distribution and dynamics of myoD -positive cells during regeneration.
Similarly, the process by which new muscle fibers are integrated into the pre-existing muscle and the role of these pre-existing fibers as a scaffold during the regenerative process needs to be better characterized.
Planarians are also useful for the study of the behavior of stem cells and muscle progenitors as animal's age, a line of investigation that may help explain the loss of muscle stem cells observed in aging mammals Sousa-Victor et al.
Finally, recent studies have suggested that planarian muscle cells may provide positional information to stem cells, thus regulating their fates. Therefore, future studies should address some of the important lacuna that we have in the field mostly related to the regulation of the planarian stem cells and muscle progenitors.
How conserved is the myogenic program in planarian stem cells compared to other systems? Is planarian myoD sufficient for the differentiation of the myogenic lineage? What about other important transcription factors such as Mef2 genes and pax7 required for myogenesis in other models? Also, the fact that mature muscle cells could provide with positional information to planarian stem cells may be of great relevance to understand the regulation of those stem cells, as the existence of a niche for their activity has not been shown so far in these animals.
Finally, recent studies have shown that, in mammals, stem cells may have different behaviors under homeostatic or regenerative scenarios meaning that different signals from their changing environments trigger specific behaviors in each situation Donati and Watt, In conclusion, planarian muscle may represent an attractive paradigm in which to study basic aspects of regeneration including stem cell biology, pattern formation, and positional information with further implications for the field of regenerative medicine.
The author confirms being the sole contributor of this work and approved it for publication. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
National Center for Biotechnology Information , U. Front Cell Dev Biol. Published online Feb 8. Author information Article notes Copyright and License information Disclaimer. Received Oct 30; Accepted Jan The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.
No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract The body-wall musculature of adult planarians consists of intricately organized muscle fibers, which after amputation are regenerated rapidly and with great precision through the proliferation and differentiation of pluripotent stem cells.
Keywords: planarian, myosin heavy chain, MyoD, regeneration, stem cells, myogenesis, myocytes, positional information. Introduction In the last 10—15 years stem cell-based regenerative medicine has emerged as a vigorous research field within the biological sciences Atala et al. Planarian musculature Platyhelminthes are acoelomate, triploblastic, bilaterally symmetrical animals that lack circulatory, skeletal, and respiratory systems.
Open in a separate window. Figure 1. Planarian myosin heavy-chain genes Myosin proteins are highly conserved in all eukaryotic cells, in which they provide the motor force necessary for different kinds of movements, including cytokinesis, phagocytosis, organelle movement, and muscle contraction Hartman and Spudich, Figure 2.
Planarian muscle regeneration Freshwater planarians are mainly known for their extraordinary regenerative capabilities. Early muscle differentiation during blastema formation Previous studies based on morphological criteria and electron microscopy suggested that the first myogenic cells within the blastema are detectable on days 2—3 of regeneration Sauzin, ; Pedersen, ; Hori, ; Morita and Best, Pharyngeal muscle regeneration The planarian pharynx is a muscular tube delimited by external and internal monostratified epithelia.
Figure 3. Restoration of the body-wall muscle pattern During regeneration, the intricate muscle fiber pattern of the body-wall musculature is not only fully restored, but also becomes a perfect extension of the pre-existing musculature. Figure 4. Muscle cells may provide positional information during regeneration During regeneration in planarians and during daily cell turnover in uncut animals , pluripotent neoblasts must differentiate into all missing cell types.
Conclusions and perspectives Freshwater planarians have a complex body-wall musculature that functions mainly as a skeletal support and during locomotion.
Author contributions The author confirms being the sole contributor of this work and approved it for publication. Conflict of interest statement The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Differentiation of myoblasts in the regenerating planarian Dugesia japonica. Cell Differ. Cytological approach to morphogenesis in the planarian blastema.
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Dorsal and ventral positional cues required for the onset of planarian regeneration may reside in differentiated cells. Identification of two distinct muscles in the planarian Dugesia japonica by their expression of myosin heavy-chain genes. Los turbelarios no presentan orificio anal. Estos animales tienen un ganglio cerebral, a partir del cual surgen dos cordones nerviosos laterales.
Ambos se conectan por fibras nerviosas que van desde uno hasta el otro. Estas son quimiorreceptores, tangorreceptores y reorreceptores. Por el contrario, hay otras que se han adaptado a vivir en ambientes de agua dulce. El esperma se almacena en una estructura denominada bolsa copulatriz. Dependiendo de la especie se observan dos tipos de huevos:. Esto quiere decir que se alimentan de otros animales. En el primer caso, ocurre gracias la presencia de una vacuola digestiva, la cual segrega enzimas digestivas exopeptidasas, lipasas.
Make sure you answer the question: Does the planarian prefer a light or dark environment and include your reasoning. Planaria prefer the dark, as evidenced by the observation that they will move away from the light and to a dark side of the dish. Drop a piece of food into the petri dish with the planarian. Observe the planarian's reactions.
It may take a few minutes. How does it eat the food? Where is its mouth? Use the space below to write your observations. Planaria often will not eat in a dish. Students always want to try this, but I rarely get good results. Caution: do not leave food in the dish as it will spoil water and probably kill the planarian if they are left in it too long. I've used piece of hot dogs, fish food, or even dog food to feed them. What is the name of the tube used for feeding in the planarian?
Pour out some of the water, so that the planarian is mostly un-submerged. When it stretches out, use a razor blade to cut it cleanly in half. Replace the water and put the lid on it.
Observe the two pieces of the planarian under the microscope or with a hand lens. Describe how each of the cut halves is behaving. Are they both moving? Is one moving more than the other? Is there obvious damage to the tissue of the animal?
Usually the head end will continue to move but the tail end will be stationary. Sometimes bits of the planarian will break off and float in the water. Students will often assume it is dead if it is not moving, which is not the case.
Dead planarian actually dissolve rather quickly, if you look at the planarian dishes in a couple of days and see no planaria, it means they did probably die. If you can see a lump of planarian it is still alive and may continue to regenerate. It takes weeks for the worms to regenerate.
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