Inhibition of cell proliferation does not slow down echinoderm neural regeneration.

Background: Regeneration of the damaged central nervous system is one of the most interesting post-embryonic developmental phenomena. Two distinct cellular events have been implicated in supplying regenerative neurogenesis with cellular material - generation of new cells through cell proliferation and recruitment of already existing cells through cell migration. The relative contribution and importance of these two mechanisms is often unknown.

Heterogeneous generation of new cells in the adult echinoderm nervous system.

Adult neurogenesis, generation of new functional cells in the mature central nervous system (CNS), has been documented in a number of diverse organisms, ranging from humans to invertebrates. However, the origin and evolution of this phenomenon is still poorly understood for many of the key phylogenetic groups. Echinoderms are one such phylum, positioned as a sister group to chordates within the monophyletic clade Deuterostomia.

Myc regulates programmed cell death and radial glia dedifferentiation after neural injury in an echinoderm.

Background: Adult echinoderms can completely regenerate major parts of their central nervous system even after severe injuries. Even though this capacity has long been known, the molecular mechanisms that drive fast and complete regeneration in these animals have remained uninvestigated. The major obstacle for understanding these molecular pathways has been the lack of functional genomic studies on regenerating adult echinoderms.

Expression of pluripotency factors in echinoderm regeneration.

Cell dedifferentiation is an integral component of post-traumatic regeneration in echinoderms. As dedifferentiated cells become multipotent, we asked if this spontaneous broadening of developmental potential is associated with the action of the same pluripotency factors (known as Yamanaka factors) that were used to induce pluripotency in specialized mammalian cells. In this study, we investigate the expression of orthologs of the four Yamanaka factors in regeneration of two different organs, the radial nerve cord and the digestive tube, in the sea cucumber Holothuria glaberrima.

Transcriptomic changes during regeneration of the central nervous system in an echinoderm.

Background: Echinoderms are emerging as important models in regenerative biology. Significant amount of data are available on cellular mechanisms of post-traumatic repair in these animals, whereas studies of gene expression are rare. In this study, we employ high-throughput sequencing to analyze the transcriptome of the normal and regenerating radial nerve cord (a homolog of the chordate neural tube), in the sea cucumber Holothuria glaberrima.

Radial glial cells play a key role in echinoderm neural regeneration.

Background: Unlike the mammalian central nervous system (CNS), the CNS of echinoderms is capable of fast and efficient regeneration following injury and constitutes one of the most promising model systems that can provide important insights into evolution of the cellular and molecular events involved in neural repair in deuterostomes. So far, the cellular mechanisms of neural regeneration in echinoderm remained obscure. In this study we show that radial glial cells are the main source of new cells in the regenerating radial nerve cord in these animals.

Retrotransposons in animal regeneration: Overlooked components of the regenerative machinery?

Research on the involvement of retroelements in developmental processes has been gaining momentum recently; however, most of the studies published so far have been focused on embryonic development. This commentary presents two recent papers, which document significant changes in transcriptional activity of retroelements in two different model systems, salamander limb regeneration and regeneration of radial organs in the sea cucumber . We hypothesize that transcriptional activity of the retrotransposons can be specifically controlled by the host and may play some hitherto unrecognized role in regeneration.

Posttraumatic regeneration involves differential expression of long terminal repeat (LTR) retrotransposons.

Background: Retrotransposons are mobile genetic elements that constitute a sizable proportion of eukaryote genomes. Although retroelements are known to play significant roles in embryogenesis, stress reactions, and disease progression, they have never been studied in the context of animal regeneration.

Results: In this study, high-throughput transcriptome analysis revealed unexpectedly large-scale changes in transcriptional activity of retrotransposons in regenerating radial organs of the sea cucumber Holothuria glaberrima.

Expression of Wnt9, TCTP, and Bmp1/Tll in sea cucumber visceral regeneration.

We employ non-radioactive in situ hybridization techniques, which combine good tissue morphology preservation with high sensitivity of transcript detection, to map gene expression in the regenerating digestive tube of the sea cucumber Holothuriaglaberrima. We investigated localization of transcripts of Wnt9, TCTP, and Bmp1/Tll, the genes that have been previously known to be implicated in embryogenesis and cancer. The choice was determined by our long-term goal of trying to understand how the developmental regulatory pathways known to be involved in tumor development can be activated in post-traumatic regeneration without leading to malignant growth.

Visceral regeneration in a sea cucumber involves extensive expression of survivin and mortalin homologs in the mesothelium.

Background: The proper balance of cell division and cell death is of crucial importance for all kinds of developmental processes and for maintaining tissue homeostasis in mature tissues. Dysregulation of this balance often results in severe pathologies, such as cancer. There is a growing interest in understanding the factors that govern the interplay between cell death and proliferation under various conditions.

Organization of glial cells in the adult sea cucumber central nervous system.

The nervous system of echinoderms has long been considered too unique to be directly comparable to the nervous system of other Deuterostomia. Using two novel monoclonal antibodies in combination with epifluorescence, confocal, and electron microscopy, we demonstrate here that the central nervous system of the sea cucumber Holothuria glaberrima possesses a major non-neuronal cell type, which shares striking similarities with the radial glia of chordates. The basic features in common include (a) an elongated shape, (b) long radial processes, (c) short lateral protrusions branching off the main processes and penetrating into the surrounding neuropile, (d) prominent orderly oriented bundles of intermediate filaments, and (e) ability to produce Reissner's substance.

The central nervous system of sea cucumbers (Echinodermata: Holothuroidea) shows positive immunostaining for a chordate glial secretion.

Background: Echinoderms and chordates belong to the same monophyletic taxon, the Deuterostomia. In spite of significant differences in body plan organization, the two phyla may share more common traits than was thought previously. Of particular interest are the common features in the organization of the central nervous system.

Regeneration of the radial nerve cord in a holothurian: a promising new model system for studying post-traumatic recovery in the adult nervous system.

After a complete transection, the radial nerve cord (RNC) of the adult sea cucumber Eupentacta fraudatrix quickly regrows and reconnects. The description of the major cellular events that accompany this regeneration is derived from light and transmission electron microscopy. Shortly after lesioning, the extensive nerve fiber degeneration and neuronal apoptosis occur.

Developmental origin of the adult nervous system in a holothurian: an attempt to unravel the enigma of neurogenesis in echinoderms.

In adult echinoderms, the nervous system includes the ectoneural and hyponeural subsystems. The former has been believed to develop from the ectoderm, whereas the latter is considered to be mesodermal in origin. However, this view has not been substantially supported by embryological examinations.

Derivation of muscles of the Aristotle's lantern from coelomic epithelia.

Transmission electron microscopy was employed to study structural changes in the lantern muscles occurring during the transition from young to adult in the sea urchin Strongylocentrotus nudus. A comparative examination of four major lantern muscles (compass depressors, compass elevators, protractors and retractors) suggests that myogenesis involves four consecutive stages. At the initial stage, the muscles show the organization of a mesentery delimited by pseudostratified coelomic epithelia, which are composed of peritoneal cells spanning the whole height of each epithelium, and myoepithelial cells, which are clustered together to fill the interstices between the basal processes of the peritoneal cells.