B: Biochem. Nevertheless, compared to previous studies, their focus was towards identifying genes associated with regeneration-related pathways. Requirement for Wnt and FGF Signaling in Xenopus Tadpole Tail Regeneration. 1 (1), 4553. This review also highlights one of the main drawbacks of current available data: the heterogeneity of the tissues and stages used to perform gene expression studies within species. Brittle star | class of echinoderms | Britannica Comp. Retrotransposon Long Interspersed Nucleotide Element1 (LINE1) Is Activated during Salamander Limb Regeneration. Physiol. The presence of these genes in a highly regenerative species, led the authors to posit that these proteins played a role in the organisms intestinal regeneration process. Echinoderms belong to the phylum Echinodermata. Radial canals lead to lateral canals which pass through pores in the skeletal plates and end in tube feet.!! Dev. 100 (10), 16791684. Creative Commons Attribution License (CC BY). 204 (1), 137143. Water vascular system. Other developmental genes commonly associated with regeneration, such as Hox and Wnt, were not found at any stage. The following sections provide a more extensive review of the molecular studies within the three categories. Mar. doi:10.1016/j.gene.2018.01.102, Viera-Vera, J., and Garca-Arrars, J. E. (2019). The Process of Regeneration. They studied the three stages previously defined by a key differentiation patterns guide (Dupont and Thorndyke, 2006) to identify 4,072 genes with significant differential expression between the selected stages compared to non-regenerating arms. A., and Helms, J. This is due, as explained above, to the possibility of drug effects on other cells, or on other cell processes that are occurring concomitantly with regeneration. protein sequence of receptors or enzymes); in the present case in the VEGF receptor that is targeted by the axitinib. Ser. Components of the retinoic acid (RA) signaling pathway were identified in the digestive tract of the sea cucumber H. glaberrima, and some of these were shown to be differentially expressed during regeneration (Viera-Vera and Garca-Arrars, 2018; Viera-Vera and Garca-Arrars, 2019). Hence, they are accordingly discussed below, along with important differences between the studies. These differences were mainly seen in the expression profiles of certain genes and the identification of new gene candidates. Moreover, there is also need for more exploratory analyses, and therefore well-curated genomes and transcriptomes. J. Exp. In contrast, morphallaxis seems to be a more complicated and slower regenerative process which tends to follow traumatic mutilations, for instance in arm tip regeneration of asteroids (Mladenov et al. Analysis of conservation demonstrated the positive selection of Wnt signaling pathway genes among echinoderms. Front. Reading and Editing the Pleurodeles waltl Genome Reveals Novel Features of Tetrapod Regeneration. The coelomate bilateria 4, 1763. This could be mainly attributed to differences in the type of tissues that were compared, different stages or the different analyses performed. 65 (4-5-6), 427437. The authors suggest that VEGF is not strictly required for skeleton formation but might be needed for establishing the patterning of the spicules. Wound Repair Regen. 4 (8), a008078. The expression patterns of genes of ECM components showed diverse regulation patterns within specific families. Glycobiology 27 (5), 438449. Transcriptomic and Proteomic Analyses of Amphiura Filiformis Arm Tissue-Undergoing Regeneration. TABLE 2. Zoology zoo chp 14 4.0 (1 review) select all of the following that are developmental characterisrics of deuterostomes Click the card to flip -formation of the mouth from a second opening ( not the blastopore) -radial regulative cleave - coelom formation by enterocoely Click the card to flip 1 / 58 Flashcards Learn Test Match Created by Trends Ecology Evolution 25 (3), 161170. As mentioned earlier, transcriptome studies provide the opportunity to discover genes that have not been previously considered to be involved in a particular process. Under physiological conditions regeneration is prompted by autotomy and proceeds from the retained side of a fractured autotomy plane. Similarly, Hox gene sequences were identified from mRNA of brittle stars regenerating arm tips (Ben Khadra et al., 2014). Further studies suggested that dedifferentiation was under the control of a GSK3, Wnt-independent pathway that remained unidentified. Tube feet used for locomotion, prey capture, adherence to substratum.! Noteworthy, they also identified the translation regulation pathways as being associated with the brittle star early arm regeneration. The subphylum Stelleroidea contains the two classes of sea stars. Gene expression studies showed that these two gene families were upregulated in early regenerating intestines. doi:10.1186/1471-2164-10-262, Pasten, C., OrtizPineda, P. A., and GarcaArrars, J. E. (2012a). 407 (2), 315322. Among these there were the development-related vascular endothelial growth factor (VEGF) pathway and cytoskeleton remodeling pathways. Echinoderms Flashcards | Quizlet One of the highlights of this study was the description of the differential expression of transcription factors. Front. This methodology was applied to the study of the Wnt pathway during regeneration by targeting -catenin, a key molecule in the intracellular Wnt signaling pathway. Interestingly, in many cases, the detached body fragments can survive in good health for a long time and undergo phenomena of partial or total regeneration independently of the donor animal (Candia Carnevali et al. Biochem. The Morphology of the Digestive Tract and Respiratory Organs of the Holothurian Cladolabes Schmeltzii (Holothuroidea, Dendrochirotida). Their results showed not only a possible role for MMPs in regeneration, but also the importance of the timing of enzymatic activity; animals that received the drug 3days after injury could not undergo wound healing and died, while animals that received the drug later (7-days) survived, and slowly regenerated. Furthermore, by correlating differential expression profiles of genes and protein products at 1- and 3-dpa, it was possible to identify pathways and processes potentially involved in the regeneration process. Similarly, FGF receptor inhibition in adults prevented skeletal spicule formation in the regenerating arms (Figure 3). August. 221 (1), 93109. Moreover, the canonical Wnt/-catenin pathway is known to play a key role in the maintenance and regeneration of the luminal stem cells of the vertebrate intestine (Cordero and Sansom 2012; Kretzschmar and Clevers 2017). Polian vesicles are known to be part of the inflammatory responses and have been suggested to be a site of origin of coelomocytes, the echinoderm immune cells. Development 148 (10), dev180760. Draft Genome of the Sea Cucumber Holothuria Glaberrima, a Model for the Study of Regeneration. It is the largest animal phylum without freshwater or land-living members. One of the most recent, is the transcriptome profiling of A. japonicus polian vesicles (Shi et al., 2020). They also identified genes involved with the cytoskeleton and ECM, such as actin and collagen genes. The subsequent decrease in Myc mRNA levels (and the expected decrease in Myc protein levels) was accompanied by a decrease in the dedifferentiation of radial glia and a decrease in cellular apoptosis. The new intestine regenerates from the tip of the mesentery to which the eviscerated intestine was attached, and the cellular events associated with the regeneration process have been well documented (Hyman, 1955; Garca-Arrars and Greenberg, 2001; Mashanov and Garca-Arrars, 2011; Garca-Arrars et al., 2019; Quispe-Parra et al., (2021b)). The echinoid larva (echinopluteus) and the ophiuroid larva (ophiopluteus) usually have four pairs of arms but may have fewer or more. doi:10.1016/j.tice.2012.10.002, Kasahara, M., Kobayashi, C., Yamanaka, A., and Kitazawa, C. (2019). Developmental Dyn. Comp. A doliolaria larva usually contains large quantities of yolk material and moves with the aid of several ciliated bands arranged in hoops around the body. A., and Palmer, A. R. (2003). doi:10.1002/jemt.1191, Viera-Vera, J., and Garca-Arrars, J. E. (2018). Sea urchins (Echinoidea) readily regenerate lost spines, pincerlike organs called pedicellariae, and small areas of the internal skeleton, or test. Evolutionary History of Regeneration in Crinoids (Echinodermata). Most have radial symmetry. Furthermore, the high expression of upstream genes (Wnt7 and Frizzled7) at early intestine regeneration and downstream genes (Myc) at advanced stages strongly suggested an early activation of the pathway upon the initiation of regeneration. Salamander-like Tail Regeneration in the West African Lungfish. Differential expression provides evidence that might suggest specific genes for a role in the regenerative processes and might also serve for the identification of novel genes in the processes. J. Inorg. The low number of differentially expressed transcripts is interesting, when considering that a total of 24,867 contigs were assembled. Regeneration in Echinoderms - Echinodermata - Barnard Health Care Biol. 1989; Moss et al. In the last decades, echinoderms have been slowly gaining special attention as model systems for regeneration studies due to their wide assortment of astonishing regenerative capacities (Hyman, 1955; Candia Carnevali and Bonasoro, 2001). This organ is similar in its histological structure to that of other metazoans and includes tissues that arise from the three different germinal layers: ectoderm, mesoderm, and endoderm. Comp. Phylum Echinodermata Groups & Reproduction | How Do Echinoderms The molecular aspects of intestinal regeneration have been studied in three holothurian species: E. fraudatrix, A. japonicus, and H. glaberrima, providing insights to regenerative processes that go beyond those that might be specific to holothurians. This project was funded by the National Institutes of Health grants (R15NS01686 and R21AG057974) to JG-A and the University of Puerto Rico. In holothuroids it is also ubiquitous but has been explored in terms of mechanisms only in a few cases (Dolmatov and Ginanova 2001; Garcia-Arraras and Greenberg 2001). The arms are spread into a characteristic fan at right angles to the prevailing current, and small prey animals are passed to the mouth along the grooves by activity of the cilia and the tube feet. doi:10.1002/jemt.1187, Candia-Carnevali, M. D., Thorndyke, M. C., and Matranga, V. (2009). Characterization of Proteolytic Activities during Intestinal Regeneration of the Sea Cucumber, Holothuria Glaberrima. Cel Tissue Res. In direct development the young usually are reared by the female parent. Echinoderms feed in a variety of ways. digestive system. As highlighted by (Quispe-Parra et al., 2021a), results obtained when comparing normal intestine to 3-dpe rudiments might correspond more to cell type-specific expression than to regeneration-associated expression. (C) Stages of intestinal regeneration in the sea cucumber H. glaberrima provide a baseline to detect the effect of regeneration modulating drugs as shown in Garca-Arrars et al., 2019. In situ hybridization and immunohistochemical techniques have been the principal techniques to localize the expression of the mRNA or protein for the genes of interest, while qRT-PCR has been used to quantify their expression. For most of them, previous experiments had shown that the molecules of interest were present in the tissues or organs studied and that they were over-expressed during the regenerative process, thus providing the rationale for their functional analyses. However, it is within the holothuroid class that multiple regeneration processes have been documented. (2019). An echinoderm ( / kandrm, k -/) [2] is any member of the phylum Echinodermata ( / kanodrmt / ). Cel Tissue Res. Tissue and Cell 59, 19. In addition to the studies of adult echinoderms described above, several investigators have focused their research on regeneration processes of echinderm larvae (Cary et al., 2019). What does echinoderms mean. B: Biol. Dev. The larva, named pluteus, resembles an artists easel turned upside down. Biochem. doi:10.1002/dvdy.23844, Mashanov, V. S., Zueva, O. R., and Garca-Arrars, J. E. (2015a). Although the ability to regenerate an arm occurs in all stellate echinoderms, differences in extent, timing, energetic costs and frequency of regeneration (Lawrence 2010) are clearly observed within and among classes. Regeneration in Echinoderms and Ascidians - Carnevali - - Major Rather than describing the whole regeneration process, the study provides an insight into the transcription factors that are potentially involved in transdifferentiation during intestinal regeneration. While the present review focuses on adult echinoderms, readers interested in larval regeneration are directed to a recent review (Wolff and Hinman, 2021) on the regeneration of sea star and sea urchin larvae that collects most of the information available on this topic. Echinoderms are known for their unique five-fold symmetry and their abilities of regeneration of limbs and wounded surfaces. PloS one 13 (4), e0195836. (2018). (2020). Regeneration in Echinoderms and Ascidians - Wiley Online Library Sand dollar, sea star, sea cucumbers, brittle stars, sea urchins. Among ophiuroids, the brittle star Amphiura filiformis has been the main species for studies on specific genes associated with regenerative processes, particularly arm regeneration. For instance, developmental genes, such as specific Hox genes, showed upregulation at earlier stages (Hox 9, 10, and 12), while others appeared upregulated at later stages (Hox 5). The study described above demonstrate the advantage of sea cucumbers as regeneration models for nerve cord regeneration. Biol. Although the results are correlative and do not provide for functional relationship between the identified genes and the regeneration process, the identification of specific genes can lead to further functionality studies. In this study the focus was on ECM-related genes, as this change in the strength of the connective tissue would not be possible without ECM remodeling. The effect of FGF signaling inhibition was studied in the regenerating arm of the brittle star A. filiformis (Czarkwiani et al., 2021). This was the first transcriptomic analysis on stages earlier than 3-dpe and the first in comparing the early regenerating intestine to the mesentery of non-regenerative animals, instead of to normal intestine. In some cases, these studies include some type of quantification of expression between regenerating structures and the normal non-injured organ. doi:10.1111/acel.12487, Boyko, A. V., Girich, A. S., Tkacheva, E. S., and Dolmatov, I. Y. A. open Sci. These phenomena, which are also quite common in asteroids, provide evidence of the wide exploitation and implications of regenerative potential in echinoderms. Such is the case with the finding that a large number of transposable elements (TEs), or transposons, were differentially expressed at different stages of radial nerve regeneration in H. glaberrima (Mashanov et al., 2012c). doi:10.1016/j.cell.2017.05.016, Ortiz-Pineda, P. A., Ramrez-Gmez, F., Prez-Ortiz, J., Gonzlez-Daz, S., Santiago-De Jess, F., Hernndez-Pasos, J., et al. Transcriptome profiling of regenerating tissues in brittle stars. (2013). Kamenev, Y. O., Dolmatov, I. Y., Frolova, L. T., and Khang, N. A. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). There are also very limited studies on the molecular regeneration in sea urchins, and most of these are also focused on the presence and differential expression of single genes associated with the regeneration of spines or pedicellaria (Dubois & Ameye, 2001). (2018). They also found members of the development associated kruppel-like family (KLF) that were upregulated in the regenerative tissues. Hence, these two reports (Rojas-Cartagena et al., 2007; Ortiz-Pineda et al., 2009) were some of the first studies to demonstrate the potential of wide transcription profiling for the identification of novel genes that were not previously considered to be involved in tissue regeneration processes. Metalloproteinase Inhibitor GM6001 Delays Regeneration in Holothurians. Some sea cucumbers remain attached to a surface for indefinite periods of time, capturing plankton in a network of branching, sticky tentacles; others select food from the seafloor and push it into their mouths with their tentacles. From these, selenoprotein W gene was highly expressed at the second stage of Burns et al. These applications have allowed scientists to divert from studying only candidate genes to perform large-scale molecular studies. In the same report, VEGF was also studied in embryos and adults, by blocking its receptor with the drug axitinib. genomics 22, 19. 316 (2), 323335. (A) Stages of arm regeneration in the brittle star A. filiformis provide a baseline to detect the effect of regeneration modulating drugs as shown in Czarkwiani et al. doi:10.1016/s0145-305x(02)00068-x, Sea Urchin Genome Sequencing Consortium (2006). Biol. doi:10.1186/s12915-019-0633-9, Clark, M. S., Dupont, S., Rossetti, H., Burns, G., Thorndyke, M. C., and Peck, L. S. (2007). The levels of -catenin mRNA in the regenerating intestinal explant were knocked-down by the electroporation of ds--catenin RNA (Alicea-Delgado and Garca-Arrars, 2021). Wnt/-catenin Signaling Pathway Regulates Cell Proliferation but Not Muscle Dedifferentiation Nor Apoptosis during Sea Cucumber Intestinal Regeneration. 381 (3), 411426. In brief, it is known that fibers and cells migrate from both nerve stumps forming a bridge that eventually gives rise to a new nerve cord region that is scar-free. Nature 425 (6954), 146. doi:10.1242/jeb.0244510.1038/425146a, Elewa, A., Wang, H., Talavera-Lpez, C., Joven, A., Brito, G., Kumar, A., and Simon, A. Skeletal Regeneration in the Brittle star Amphiura Filiformis. For example, Wnt has been associated with Hydra apical regeneration (Vogg et al., 2019), the establishment of axial polarity in regenerating Planaria (Almuedo-Castillo et al., 2012) and tail regeneration in zebrafish and in Xenopus tadpole (Stoick-Cooper et al., 2007; Lin and Slack, 2008) among others. doi:10.1016/j.gep.2013.09.002, Czarkwiani, A., Ferrario, C., Dylus, D. V., Sugni, M., and Oliveri, P. (2016). There are two ways by which evisceration occurs in sea cucmber species: from the mouth (anterior) or the anus (posterior). Breed. One of the first pharmacological studies performed, targeted the matrix metalloproteinases (MMPs) as a way of studying their function in the extracellular matrix remodeling shown to take place during intestinal regeneration in H. glaberrima (Quiones et al., 2002). Both drugs reduced cellular proliferation in the intestinal rudiment, however MG132 treated animals showed a reduction in the size of the rudiment while E64d treated animals showed a delay in the degradation of collagen. flatworm. Gene Expression Profiling of Intestinal Regeneration in the Sea Cucumber. After a holothurian has autoeviscerated, it is unable to feed during the several weeks required for gut regeneration. doi:10.1038/s41598-020-79436-2, Quispe-Parra, D., Valentn, G., and Garca-Arrars, J. E. (2021b). Acta Physiol. (2017). doi:10.1002/jez.b.22899, Kondo, M., and Akasaka, K. (2010). As expected, this analysis yielded a higher percentage of characterized genes, compared to the first report. Terminal tubefeet are . Science 314 (5801), 941952. doi:10.1111/j.1440-169X.2009.01159.x, Kretzschmar, K., and Clevers, H. (2017). The EST sequence profiling identified 5,173 differentially expressed sequences from intestinal rudiments of 3- and 7-days post evisceration (dpe) (Rojas-Cartagena et al., 2007). Echinoderms can perform asexual reproduction by fragmentation and cleaving off a portion of its body to regenerate a new one. doi:10.1016/j.cbpb.2017.06.005, Lin, G., and Slack, J. M. (2008). Dyn. It is important to highlight that while there are numerous echinoderm molecular studies, here we only focus on those directed to their regeneration potential. doi:10.1016/j.fsi.2019.12.016, Smith, G. N. (1971). Using this model system, multiple Wnt pathway modulating drugs were tested. In a similar way, retrotransposons accounted for about 33% of genes identified during fission initiation in C. schmeltzii (Dolmatov et al., 2018). Furthermore, numerous developmental transcripts with high regulation were identified including frizzled (Wnt pathway), Notch, Delta (Notch pathway), and BMP (TGF-beta pathway). Transcriptome Pyrosequencing of the Antarctic Brittle star Ophionotus Victoriae. RNA-seq Reveals Dynamic Changes of Gene Expression in Key Stages of Intestine Regeneration in the Sea Cucumber Apostichopus Japonicas. doi:10.1016/j.ydbio.2017.09.035, Flowers, G. P., and Crews, C. M. (2018). Retinoic Acid Signaling Is Associated with Cell Proliferation, Muscle Cell Dedifferentiation, and Overall Rudiment Size during Intestinal Regeneration in the Sea Cucumber, Holothuria Glaberrima. (2018). Development 146 (21), dev177212. In holothurians, the initial studies addressing the molecular basis of intestinal regeneration were directed to the determination of changes in gene expressions. Homeobox Genes Expressed during Echinoderm Arm Regeneration. Complementary to this revision we would like to direct the readers to two previous reviews on the topic that provide some of the first insights into this area of research (Thorndyke et al., 2001; Mashanov and Garca-Arrars, 2011) and to a recent comprehensive review by Dolmatov (2021) on the molecular aspects of regeneration mechanisms in holothurians. Sci. Similarly in holothuroids, studies have questioned the use of adult normal intestines as being the appropriate comparisons for early regeneration intestines to determine differential gene expression due to dissimilarities in tissue layer composition. Both stages shared a total of 3,884 differentially expressed transcripts. The authors also performed a comparative transcriptomic study between animals regenerating their arms in the presence and absence of the Notch pathway inhibitor. zoo chp 14 Flashcards | Quizlet However, no effect on apoptosis or cell dedifferentiation occurred. How Do Echinoderms Get Their Food - Micro B Life Regeneration in the Sea Cucumber Leptosynapta. Echinodermata is Greek for "spiny skinned." Starfish are also known as sea stars. Visceral Regeneration in a Sea Cucumber Involves Extensive Expression of Survivin and Mortalin Homologs in the Mesothelium. Furthermore, there were development-associated genes that were expressed. In contrast, transforming growth factor beta-2 (Tgfb2), AT-rich interaction domain 1b (ARID1b), SIPA, and N-ethylmaleimide-sensitive fusion protein (NSF) were at the top of the downregulated transcripts list. The analysis yielded differentially expressed genes related to response to stimulation, muscle contraction, metabolism, ECM and secretion of neurotransmitters. doi:10.1002/1097-010X(20001215)288:4<335:AID-JEZ6>3.0.CO;2-1, Santiago-Cardona, P. G., Berros, C. A., Ramrez, F., and Garca-Arrars, J. E. (2003). Starfish are also known as sea stars. The third category comprises the studies where the functions of the candidate genes are tested. doi:10.1098/rspb.2003.2367, Patruno, M., Smertenko, A., Candia Carnevali, M. D., Bonasoro, F., Beesley, P. W., and Thorndyke, M. C. (2002). The study yielded the differential expression of 8,460 transcripts at 1-dpe and 8,216 at 3-dpe. doi:10.1371/journal.pone.0069441, Thorndyke, M. C., Chen, W. C., Beesley, P. W., and Patruno, M. (2001). This high number of transcription factors is thought to be due to the regeneration processes that begin right after the division of the animal. The most recent addition to the transcriptomic studies of holothurian intestinal regeneration is an in-depth study using RNA-seq on early stages of intestinal regeneration of H. glaberrima (Quispe-Parra et al., 2021a). Thus, multiple studies on TE sequences demonstrate their expression in a dynamic manner, suggesting a functional role in the regeneration processes. This study was centered on the transdifferentiation mechanism of mesodermal cells as part of the regeneration process, since in this species, the coelomic epithelia of the anterior regenerating intestine gives rise to the luminal epithelia (Boyko et al., 2020). Most studies performed to determine the role of particular molecules or pathways during echinoderm regeneration have been done using specific drugs that inhibit enzymes, receptors or components of a signal pathway. Echinoderms may also reproduce asexually, as well as regenerate body parts lost in trauma. Genet. Patterns 12 (1-2), 2435. Specifically, at the third stage the expression of hyalin and Sox1 genes decreased, while BMP-1 homolog, which was downregulated at the first stage, increased its expression to normal levels. This phylum includes 7,000 living species. 17 (1), 119. In addition, even in the best cases, the specificity of the drugs has to be questioned. 15 (10), e2003790. doi:10.1387/ijdb.113451ma, Amemiya, S., and Oji, T. (1992). Echinoderms (starfish, brittle star, sea urchin, feather star, sea Even though echinoderms are closely related to chordates, they are little known in the biomedical field, and therefore their uses to study pharmacological effects on muscle formation and/or regeneration have been extremely limited. doi:10.1371/journal.pone.0195836, Dolmatov, I. Y. Successful fragmentation and regeneration require a body wall that can be torn and an ability to seal resultant wounds. Microsc. (2011), Burns et al. Nature 554 (7690), 3435. This makes further exploratory molecular studies on crinoids, echinoids, and asteroids essential in order to obtain a broader overview of the molecules that act during regeneration. Tech. While the focus of regeneration studies in holothurians has been the intestine, regeneration of other tissues and organs has also been investigated. Specifically, studies targeting the regeneration of their digestive tract, exemplify their suitability as regeneration model. This is called external fertilization and is typical of many marine animals. Int. Part D: Genomics Proteomics 6 (2), 195205. The overall conclusion of the experiments was that the canonical Wnt/-catenin pathway was responsible for the increase in cell proliferation associated with intestinal regeneration, but it had no effect on two other cellular events: muscle cell dedifferentiation nor apoptosis. R. Soc. Res. 288 (4), 335344. doi:10.3354/ab00004, Cordero, J. Zoolog. Echinoderms belong to the phylum Echinodermata. Tech. Aquat. Model Systems for Regeneration: Hydra. Water vascular system! This will provide the basis for comparative analyses establishing unique molecular characteristics that might be responsible for the amazing regenerative processes observed in echinoderms. Molecular studies of regeneration favor certain echinoderm classes over others. In this study, a total of 1,978 upregulated and 2,434 downregulated transcripts were identified in samples treated with a Notch pathway inhibitor. The expression and role of Myc was the focus of other regeneration studies in this species (see below). Feeding methods of concentricycloids are not yet known. Biol. Other highly expressed genes identified were associated to cell proliferation, division, and apoptosis (e.g., cleavage stimulation factor, polyubiquitin, proteasome, actin, and collagen). Biol. Among the enriched pathways identified are ribosome, proteasome, development, signaling (e.g., Notch, TGF-beta, Wnt), and metabolic pathways. It has fragile arms formed by lobes of ciliated bands and is supported by fragile rods of calcite, the skeletal material. Other than the above studies on A. filiformis arm regeneration, transcriptomic studies have been performed on two other brittle star species. J. Exp. at the level of the autotomy plane. Thus, the Wnt pathway genes fulfill two of the requirements for a potential role (or roles) in the intestinal regeneration process: 1) genes associated with the pathway are expressed in cells of the regenerating intestinal rudiment and 2) some of these genes show differential expression associated with specific stages of the regeneration process.
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