Regeneration of the digestive system in the crinoid Himerometra robustipinna occurs by transdifferentiation of neurosecretory-like cells

Regeneration of the digestive system in the crinoid Lamprometra palmata (Mariametridae, Comatulida)

The morphology and regeneration of the digestive system and tegmen after autotomy of the visceral mass in the crinoid Lamprometra palmata (Clark 1921) was studied. The gut has a five-lobed shape and is covered by a tegmen. The tegmen consists of epidermis and underlying connective tissue. The digestive tube can be divided into three parts: esophagus, intestine, and rectum. At 6 h post-autotomy, the calyx surface is covered by a layer of amoebocytes and juxtaligamental cells (JLCs). At 14-18 h, post-autotomy transdifferentiation of JLCs begins and give rise to the epidermis and cells of digestive system. On days 1-2 post-autotomy, JLCs undergo the mesenchymal-epithelial transition. Some JLCs turn into typical epidermal cells, while other JLCs form small closed epithelial structures that represent the gut anlage. On day 4 post-autotomy, the animals have a mouth opening and a small anal cone. On day 7 post-autotomy, the visceral mass and the digestive system become fully formed but are smaller than normal. A 24-h exposure of L. palmata individuals to a 10^-7 M colchicine solution did not slow down regeneration, and the timing of gut formation was similar to that in the control animals. We conclude that JLCs are the major cell source for gut and epidermis regeneration in L. palmata. The main mechanisms of morphogenesis are cell migration, mesenchymal-epithelial transition, and transdifferentiation.

The Role of the Microbiota in Regeneration-Associated Processes

The microbiota, the set of microorganisms associated with a particular environment or host, has acquired a prominent role in the study of many physiological and developmental processes. Among these, is the relationship between the microbiota and regenerative processes in various organisms. Here we introduce the concept of the microbiota and its involvement in regeneration-related cellular events. We then review the role of the microbiota in regenerative models that extend from the repair of tissue layers to the regeneration of complete organs or animals. We highlight the role of the microbiota in the digestive tract, since it accounts for a significant percentage of an animal microbiota, and at the same time provides an outstanding system to study microbiota effects on regeneration. Lastly, while this review serves to highlight echinoderms, primarily holothuroids, as models for regeneration studies, it also provides multiple examples of microbiota-related interactions in other processes in different organisms.

A pan-metazoan concept for adult stem cells: the wobbling Penrose landscape

Adult stem cells (ASCs) in vertebrates and model invertebrates (e.g. Drosophila melanogaster) are typically long-lived, lineage-restricted, clonogenic and quiescent cells with somatic descendants and tissue/organ-restricted activities. Such ASCs are mostly rare, morphologically undifferentiated, and undergo asymmetric cell division. Characterized by 'stemness' gene expression, they can regulate tissue/organ homeostasis, repair and regeneration. By contrast, analysis of other animal phyla shows that ASCs emerge at different life stages, present both differentiated and undifferentiated phenotypes, and may possess amoeboid movement. Usually pluri/totipotent, they may express germ-cell markers, but often lack germ-line sequestering, and typically do not reside in discrete niches. ASCs may constitute up to 40% of animal cells, and participate in a range of biological phenomena, from whole-body regeneration, dormancy, and agametic asexual reproduction, to indeterminate growth. They are considered legitimate units of selection. Conceptualizing this divergence, we present an alternative stemness metaphor to the Waddington landscape: the 'wobbling Penrose' landscape. Here, totipotent ASCs adopt ascending/descending courses of an 'Escherian stairwell', in a lifelong totipotency pathway. ASCs may also travel along lower stemness echelons to reach fully differentiated states. However, from any starting state, cells can change their stemness status, underscoring their dynamic cellular potencies. Thus, vertebrate ASCs may reflect just one metazoan ASC archetype.

Ultrastructural changes associated to the neuroendocrine transdifferentiation of the lung adenocarcinoma cell line A549

The neuroendocrine transdifferentiation has been found in many cancer cell types, such as prostate, lung and gastrointestinal cells and is accompanied by a lower patient life expectancy. The transdifferentiation process has been induced in vitro by the exposure to different stimuli in human lung adenocarcinoma. The aim of this work was to identify the morphological characteristics of the neuroendocrine phenotype in a human lung cancer cell line, induced by two cAMP elevating agents (IBMX and FSK). Our results showed two phenotypes, one produced by IBMX with higher volume, cell size and increased number of secondary projections, and the other produced by FSK with higher area, roughness of the membrane, cell neurite percentage, number of outgrowths per cell and increased number of primary projections. In conclusion, we describe some morphological and ultrastructural characteristics of the neuroendocrine phenotype in A549 human lung cancer cell line promoted by IBMX and FSK to contribute to the understanding of the autocrine or paracrine signaling within the tumor microenvironment.

Molecular Aspects of Regeneration Mechanisms in Holothurians

Holothurians, or sea cucumbers, belong to the phylum Echinodermata. They show good regenerative abilities. The present review provides an analysis of available data on the molecular aspects of regeneration mechanisms in holothurians. The genes and signaling pathways activated during the asexual reproduction and the formation of the anterior and posterior parts of the body, as well as the molecular mechanisms that provide regeneration of the nervous and digestive systems, are considered here. Damage causes a strong stress response, the signs of which are recorded even at late regeneration stages. In holothurian tissues, the concentrations of reactive oxygen species and antioxidant enzymes increase. Furthermore, the cellular and humoral components of the immune system are activated. Extracellular matrix remodeling and Wnt signaling play a major role in the regeneration in holothurians. All available morphological and molecular data show that the dedifferentiation of specialized cells in the remnant of the organ and the epithelial morphogenesis constitute the basis of regeneration in holothurians. However, depending on the type of damage, the mechanisms of regeneration may differ significantly in the spatial organization of regeneration process, the involvement of different cell types, and the depth of reprogramming of their genome (dedifferentiation or transdifferentiation).

Beyond Adult Stem Cells: Dedifferentiation as a Unifying Mechanism Underlying Regeneration in Invertebrate Deuterostomes

The diversity of regenerative phenomena seen in adult metazoans, as well as their underlying mechanistic bases, are still far from being comprehensively understood. Reviewing both ultrastructural and molecular data, the present work aims to showcase the increasing relevance of invertebrate deuterostomes, i.e., echinoderms, hemichordates, cephalochordates and tunicates, as invaluable models to study cellular aspects of adult regeneration. Our comparative approach suggests a fundamental contribution of local dedifferentiation -rather than mobilization of resident undifferentiated stem cells- as an important cellular mechanism contributing to regeneration in these groups. Thus, elucidating the cellular origins, recruitment and fate of cells, as well as the molecular signals underpinning tissue regrowth in regeneration-competent deuterostomes, will provide the foundation for future research in tackling the relatively limited regenerative abilities of vertebrates, with clear applications in regenerative medicine.

Collective Locomotion of Human Cells, Wound Healing and Their Control by Extracts and Isolated Compounds from Marine Invertebrates

The collective migration of cells is a complex integrated process that represents a common theme joining morphogenesis, tissue regeneration, and tumor biology. It is known that a remarkable amount of secondary metabolites produced by aquatic invertebrates displays active pharmacological properties against a variety of diseases. The aim of this review is to pick up selected studies that report the extraction and identification of crude extracts or isolated compounds that exert a modulatory effect on collective cell locomotion and/or skin tissue reconstitution and recapitulate the molecular, biochemical, and/or physiological aspects, where available, which are associated to the substances under examination, grouping the producing species according to their taxonomic hierarchy. Taken all of the collected data into account, marine invertebrates emerge as a still poorly-exploited valuable resource of natural products that may significantly improve the process of skin regeneration and restrain tumor cell migration, as documented by in vitro and in vivo studies. Therefore, the identification of the most promising invertebrate-derived extracts/molecules for the utilization as new targets for biomedical translation merits further and more detailed investigations.

The Eupentacta fraudatrix transcriptome provides insights into regulation of cell transdifferentiation

The holothurian Eupentacta fraudatrix is a unique organism for studying regeneration mechanisms. Moreover, E. fraudatrix can quickly restore parts of its body and entire organ systems, yet at the moment, there is no data on the participation of stem cells in the process. To the contrary, it has been repeatedly confirmed that this process is only due to the transformation of terminally differentiated cells. In this study, we examine changes in gene expression during gut regeneration of the holothurian E. fraudatrix. Transcriptomes of intestinal anlage of the three stages of regeneration, as well as the normal gut, were sequenced with an Illumina sequencer (San Diego, CA, USA). We identified 14,617 sea urchin protein homologs, of which 308 were transcription factors. After analysing the dynamics of gene expression during regeneration and the map of biological processes in which they participate, we identified 11 factors: Ef-EGR1, Ef-ELF, Ef-GATA3, Ef-ID2, Ef-KLF1/2/4, Ef-MSC, Ef-PCGF2, Ef-PRDM9, Ef-SNAI2, Ef-TBX20, and Ef-TCF24. With the exception of TCF24, they are all involved in the regeneration, development, epithelial-mesenchymal transition, and immune response in other animals. We suggest that these transcription factors may also be involved in the transdifferentiation of coelomic epithelial cells into enterocytes in holothurians.

Crinoid respiration and the distribution of energetic strategies among marine invertebrates

During the Mesozoic, the radiation of durophagous marine predators caused the ecological and evolutionary diminution of once-successful groups, including stalked, suspension-feeding echinoderms known as crinoids. Featherstars, crinoids that shed the stalk during development and exhibit anti-predatory adaptations such as high motility, defied this trend, and today they are widespread and diverse across ocean depths. As a ‘success story’ of the Mesozoic Marine Revolution, featherstars could be used to reveal how some marine lineages succeeded in the face of increased predation over geological time. However, current limited understanding of crinoid functional anatomy has inhibited such study. Using microphotography, scanning electron microscopy and computed tomography, I characterize the structure and variation of crinoid circulatory anatomy and explore differences between featherstars and stalked forms. Contrary to previous accounts, I find support for the role of coelomic circulation in crinoid respiration. This includes a previously undocumented case of positive allometry: larger crinoids have more complex circulatory anatomy. Moreover, quantitative analysis of coelomic anatomy shows that the circulatory system is generally more complex in featherstars than in stalked crinoids. The adaptations that allowed featherstars to persist in shallow water apparently entailed an increase in the functional capacity of the circulatory system, possibly due to consistently greater metabolic rates.

Injury affects coelomic fluid proteome of the common starfish, Asterias rubens

Echinoderms, possessing outstanding regenerative capabilities, provide a unique model system for the study of response to injury. However, little is known about the proteomic composition of coelomic fluid, an important biofluid circulating throughout the animal's body and reflecting the overall biological status of the organism. In this study, we used LC-MALDI tandem mass spectrometry to characterize the proteome of the cell-free coelomic fluid of the starfish Asterias rubens and to follow the changes occurring in response to puncture wound and blood loss. In total, 91 proteins were identified, of which 61 were extracellular soluble and 16 were bound to the plasma membrane. The most represented functional terms were 'pattern recognition receptor activity' and 'peptidase inhibitor activity'. A series of candidate proteins involved in early response to injury was revealed. Ependymin, β-microseminoprotein, serum amyloid A and avidin-like proteins, which are known to be involved in intestinal regeneration in the sea cucumber, were also identified as injury-responsive proteins. Our results expand the list of proteins potentially involved in defense and regeneration in echinoderms and demonstrate dramatic effects of injury on the coelomic fluid proteome.

Sewing up the wounds : The epithelial morphogenesis as a central mechanism of calcaronean sponge regeneration

Sponges (Porifera) demonstrate prominent regeneration abilities and possess a wide variety of mechanisms, used during this process. In the current study, we combined in vivo observations with histological, immunohistochemical, and ultrastructural technics to elucidate the fine cellular mechanisms of the regeneration in the calcareous sponge Leucosolenia cf. variabilis. The regeneration of Leucosolenia cf. variabilis ends within 4-6 days. The crucial step of the process is the formation of the transient regenerative membrane, formed by the epithelial morphogenesis-spreading of the intact exopinacoderm and choanoderm. The spreading of the choanoderm is accompanied by the transdifferentiation of the choanocytes. The regenerative membrane develops without any contribution of the mesohyl cells. Subsequently, the membrane gradually transforms into the body wall. The cell proliferation is neither affected nor contributes to the regeneration at any stage. Thus, Leucosolenia cf. variabilis regeneration relies on the remodeling of the intact tissues through the epithelial morphogenesis, accompanied by the transdifferentiation of some differentiated cell types, which makes it similar to the regeneration in homoscleromorphs and eumetazoans.