Postembryonic Organogenesis of the Digestive Tube

Abstract

We provide an integrative view of mechanisms that enable regeneration of the digestive tube in various animal models, including vertebrates, tunicates, echinoderms, insects, and flatworms. Two main strategies of regeneration of the endodermal luminal (mucosal) epithelium have evolved in metazoans. One of them involves proliferation of resident epithelial cells, while the other relies on recruitment of cells from extramucosal sources. In any of these two scenarios, either pluri-/multipotent stem cells or specialized differentiated cells can be used as the starting material. Posttraumatic visceral regeneration shares some common mechanisms with normal embryonic development as well as with organ homeostatic maintenance, but there are signaling pathways and/or cellular pools that are specific to the regenerative phenomena. Comparative analysis of the literature suggests that mammals share with spontaneously regenerating animals many of the regeneration-related adaptations and are able to efficiently repair components of their digestive tube at the level of individual tissues, but fail to do so at the whole-organ scale. We review what might cause this failure in the context of the current state of knowledge about various regenerative models. If the latent capacity for regeneration persists […], then the restoration of its overt expression should be possible if the mechanisms of its inhibition could be discovered and eventually rendered ineffectualRichard Goss (1992)

The sea cucumber genome provides insights into morphological evolution and visceral regeneration

“…In fact, the key pathways of stem cell pluripotency were considerably conserved as compared to mammals (S18 Fig). Consistent with the phylogenetic position of echinoderms (sister group to chordates), our results show that sea cucumbers share similar characteristics with vertebrates in regard to regeneration, supporting the hypothesis that regenerative mechanisms might be conserved across evolution in the Deuterostomia [62,63]. Meanwhile, some exclusive or significantly expanded genes, such as PSP94-like proteins and FREPs, might play key roles in the remarkable regenerative capacity of sea cucumbers.…”

Radial glia and radial glia-like cells: Their role in neurogenesis and regeneration

“…In H. glaberrima, RGLCs represent 60-70% of the cells in the RNCs consisting of most, if not all, glial cells present (Mashanov et al, 2010;Mashanov and Zueva, 2020). Mashanov et al (2015a) outlined the general similarities of the echinoderm RGLC and vertebrate RGCs in their published chapter on the NS of the Echinodermata: "(i) orthogonal orientation of the cell's main axis to the plane of the neuroepithelium; (ii) highly elongated shape of the cells allowing them to span the entire thickness of the neuroepithelium between the apical and basal surfaces, (iii) long thick bundles of intermediate filaments, which run mostly along the main axis of the cell and fill almost the entire intracellular space of the glial processes, (iv) short protrusions branching off at a right angles from the main processes and penetrating into the surrounding neural parenchyma" and (v) the expression of a "material similar to the so-called Reissner's substance of chordates". These species share the presence of cells with neurogenic properties.…”

Single-cell RNA sequencing of the holothurian regenerating intestine reveals the pluripotency of the coelomic epithelium

“…This extraordinary ability makes them a valuable model for studying regeneration in complex organisms. The regeneration of the digestive system in holothurians, in particular, has garnered significant interest (Dolmatov, 2021; Mashanov et al, 2014; Medina-Feliciano and García-Arrarás, 2021; Quispe-Parra et al, 2021; Su et al, 2022). Upon evisceration, the holothurian intestine, which constitutes nearly their entire digestive tract, begins to regenerate from the mesentery, a supportive tissue layer where the original intestine was attached (García-Arrarás et al, 1998).…”