Berberine exposure triggers developmental effects on planarian regeneration.

The mechanisms of action underlying the pharmacological properties of the natural alkaloid berberine still need investigation. Planarian regeneration is instrumental in deciphering developmental responses following drug exposure. Here we report the effects of berberine on regeneration in the planarian Dugesia japonica. Our findings demonstrate that this compound perturbs the regenerative pattern. By real-time PCR screening for the effects of berberine exposure on gene expression, we identified alterations in the transcriptional profile of genes representative of different tissues, as well as of genes involved in extracellular matrix (ECM) remodeling. Although berberine does not influence cell proliferation/apoptosis, our experiments prove that this compound causes abnormal regeneration of the planarian visual system. Potential berberine-induced cytotoxic effects were noticed in the intestine. Although we were unable to detect abnormalities in other structures, our findings, sustained by RNAi-based investigations, support the possibility that berberine effects are critically linked to anomalous ECM remodeling in treated planarians.

Integrative taxonomy of a new species of planarian from the Lake Ohrid basin, including an analysis of biogeographical patterns in freshwater triclads from the Ohrid region (Platyhelminthes, Tricladida, Dugesiidae).

A new species of the genus Dugesia is described from the Lake Ohrid region in the western part of the Balkan Peninsula, forming the first fully documented species description for this genus in the Ohrid area. The morphological species delimitation is supported by complementary molecular, karyological, and cytogenetic data available from the literature. Therefore, species delineation is based on a truly integrative approach. Further, a short account on the degree of freshwater planarian endemicity in the Ohrid region is provided.

Planarians as a model to assess in vivo the role of matrix metalloproteinase genes during homeostasis and regeneration.

Matrix metalloproteinases (MMPs) are major executors of extracellular matrix remodeling and, consequently, play key roles in the response of cells to their microenvironment. The experimentally accessible stem cell population and the robust regenerative capabilities of planarians offer an ideal model to study how modulation of the proteolytic system in the extracellular environment affects cell behavior in vivo. Genome-wide identification of Schmidtea mediterranea MMPs reveals that planarians possess four mmp-like genes. Two of them (mmp1 and mmp2) are strongly expressed in a subset of secretory cells and encode putative matrilysins. The other genes (mt-mmpA and mt-mmpB) are widely expressed in postmitotic cells and appear structurally related to membrane-type MMPs. These genes are conserved in the planarian Dugesia japonica. Here we explore the role of the planarian mmp genes by RNA interference (RNAi) during tissue homeostasis and regeneration. Our analyses identify essential functions for two of them. Following inhibition of mmp1 planarians display dramatic disruption of tissues architecture and significant decrease in cell death. These results suggest that mmp1 controls tissue turnover, modulating survival of postmitotic cells. Unexpectedly, the ability to regenerate is unaffected by mmp1(RNAi). Silencing of mt-mmpA alters tissue integrity and delays blastema growth, without affecting proliferation of stem cells. Our data support the possibility that the activity of this protease modulates cell migration and regulates anoikis, with a consequent pivotal role in tissue homeostasis and regeneration. Our data provide evidence of the involvement of specific MMPs in tissue homeostasis and regeneration and demonstrate that the behavior of planarian stem cells is critically dependent on the microenvironment surrounding these cells. Studying MMPs function in the planarian model provides evidence on how individual proteases work in vivo in adult tissues. These results have high potential to generate significant information for development of regenerative and anti cancer therapies.

The in vivo effect of chelidonine on the stem cell system of planarians.

The presence of adult pluripotent stem cells and the amazing regenerative capabilities make planarian flatworms an extraordinary experimental model to assess in vivo the effects of substances of both natural and synthetic origin on stem cell dynamics. This study focuses on the effects of chelidonine, an alkaloid obtained from Chelidonium majus. The expression levels of molecular markers specific for stem or differentiated cells were compared in chelidonine-treated and control planarians. The use of these markers demonstrates that chelidonine produces in vivo a significant anti-proliferative effect on planarian stem cells in a dose-dependent fashion. In response to chelidonine treatment mitotic abnormalities were also observed and the number of cells able to proceed to anaphase/telophase appeared significantly reduced with respect to the controls. Our results support the possibility that chelidonine acts on cell cycle progression by inhibition of tubulin polymerization. These studies provide a basis for preclinical evaluation in vivo of the effects of chelidonine on physiologically proliferating stem cells.

Stem cell protection mechanisms in planarians: the role of some heat shock genes.

Planarians contain a large population of stem cells, named neoblasts, and use these for continuous turnover of all cell types. In addition, thanks to the amazing flexibility of these cells, planarians respond well to the effects of stressful situations, for example activating regeneration after trauma. How neoblasts respond to stress and support continuous proliferation, maintaining long-term stability, is still an open question. Heat shock proteins (HSPs) are a complex protein family with key roles in maintaining protein homeostasis, as well as in apoptosis and growth-related processes. We recently characterized some planarian homologs of hsp genes that are highly expressed in mammalian stem cells, and observed that some of them are critical for neoblast survival/maintenance. The results of these studies support the notion that some HSPs play crucial roles in the modulation of pathways regulating stem cell activity, regeneration and tissue repair. In this review we compare the evidence available for planarian hsp genes and focus on questions emerging from these results.

Expression of hsp90 mediates cytoprotective effects in the gastrodermis of planarians.

Heat shock proteins (HSPs) play a crucial role in the protection of cells. In the present study, we have identified an hsp90-related gene (Djhsp90) encoding a cytosolic form of HSP90 that is primarily expressed in gastrodermis of the planarian Dugesia japonica. Djhsp90 becomes significantly induced after traumatic amputation or other stress stimuli, such as exposure to X-ray or ultraviolet radiations, heat shock, or prolonged starvation. When Djhsp90 is silenced by ribonucleic acid interference (RNAi), planarians dramatically decrease in size, becoming unable to eat, and die in a few weeks. Our results indicate that this gene plays an essential cytoprotective role in the gastrodermis of planarians and suggest that this chaperone can be involved in autophagic processes that are activated by this tissue.

A mortalin-like gene is crucial for planarian stem cell viability.

In adult organisms, stem cells are crucial to homeostasis and regeneration of damaged tissues. In planarians, adult stem cells (neoblasts) are endowed with an extraordinary replicative potential that guarantees unlimited replacement of all differentiated cell types and extraordinary regenerative ability. The molecular mechanisms by which neoblasts combine long-term stability and constant proliferative activity, overcoming the impact of time, remain by far unknown. Here we investigate the role of Djmot, a planarian orthologue that encodes a peculiar member of the HSP70 family, named Mortalin, on the dynamics of stem cells of Dugesia japonica. Planarian stem cells and progenitors constitutively express Djmot. Transient Djmot expression in differentiated tissues is only observed after X-ray irradiation. DjmotRNA interference causes inability to regenerate and death of the animals, as a result of permanent growth arrest of stem cells. These results provide the first evidence that an hsp-related gene is essential for neoblast viability and suggest the possibility that high levels of Djmot serve to keep a p53-like protein signaling under control, thus allowing neoblasts to escape cell death programs. Further studies are needed to unravel the molecular pathways involved in these processes.

Two msh/msx-related genes, Djmsh1 and Djmsh2, contribute to the early blastema growth during planarian head regeneration.

Regeneration in planarians is an intriguing phenomenon, based on the presence of pluripotent stem cells, known as neoblasts. Following amputation, these cells activate mitotic divisions, migrate distally and undergo differentiation, giving rise to the regeneration blastema. We have identified two msh/msx-related genes, Djmsh1 and Djmsh2, which are expressed in distinct cell populations of the planarian Dugesia japonica and activated, with different patterns, during head regeneration. We demonstrate that RNA interference of Djmsh1 or Djmsh2 generates a delay in the growth of cephalic blastema, interfering with the dynamics of mitoses during its initial formation. Our data also reveal that the activity of the two planarian msh genes is required to regulate Djbmp expression during head regeneration. This study identifies, for the first time, a functional association between muscle segment homeobox (MSH) homeoproteins and BMP signaling during stem cell-based regeneration of the planarian head and provides a functional analysis of how msh genes may regulate in vivo the regenerative response of planarian stem cells.

Expression of a retinal homeobox (Rx) gene during planarian regeneration.

Retinal homeobox (Rx) genes, with representatives in vertebrates and invertebrates, encode fundamental regulators of early eye and brain formation. Here we describe the spatio-temporal expression profile of a candidate planarian orthologue of Rx during regeneration in Dugesia japonica and Schmidtea mediterranea. Although low levels of Rx transcripts were found throughout the body of intact planarians, high levels of Rx expression were specific to regenerating tissue in both head and tail fragments. We also observed that Rx was never expressed in the simple rhabdomeric planarian eyes, supporting the notion that only formation of eyes that use the ciliary type of photoreceptors requires Rx function.

Deciphering the molecular machinery of stem cells: a look at the neoblast gene expression profile.

BACKGROUND: Mammalian stem cells are difficult to access experimentally; model systems that can regenerate offer an alternative way to characterize stem cell related genes. Planarian regeneration depends on adult pluripotent stem cells--the neoblasts. These cells can be selectively destroyed using X-rays, enabling comparison of organisms lacking stem cells with wild-type worms. RESULTS: Using a genomic approach we produced an oligonucleotide microarray chip (the Dj600 chip), which was designed using selected planarian gene sequences. Using this chip, we compared planarians treated with high doses of X-rays (which eliminates all neoblasts) with wild-type worms, which led to identification of a set of putatively neoblast-restricted genes. Most of these genes are involved in chromatin modeling and RNA metabolism, suggesting that epigenetic modifications and post-transcriptional regulation are pivotal in neoblast regulation. Comparing planarians treated with low doses of X-rays (after which some radiotolerant neoblasts re-populate the planarian body) with specimens irradiated with high doses and unirradiated control worms, we identified a group of genes that were upregulated as a consequence of low-dose X-ray treatment. Most of these genes encode proteins that are known to regulate the balance between death and survival of the cell; our results thus suggest that genetic programs that control neoblast cytoprotection, proliferation, and migration are activated by low-dose X-rays. CONCLUSION: The broad differentiation potential of planarian neoblasts is unparalleled by any adult stem cells in the animal kingdom. In addition to our validation of the Dj600 chip as a valuable platform, our work contributes to elucidating the molecular mechanisms that regulate the self-renewal and differentiation of neoblasts.

DjPiwi-1, a member of the PAZ-Piwi gene family, defines a subpopulation of planarian stem cells.

Planarian regeneration, based upon totipotent stem cells, the neoblasts, provides a unique opportunity to study in vivo the molecular program that defines a stem cell. In this study, we report the identification of DjPiwi-1, a planarian homologue of Drosophila Piwi. Expression analysis showed that DjPiwi-1 transcripts are preferentially accumulated in small cells distributed along the midline of the dorsal parenchyma. DjPiwi-1 transcripts were not detectable after X-ray irradiation by whole mount in situ hybridization. Real time reverse transcriptase polymerase chain reaction analysis confirmed the significant reduction of DjPiwi-1 expression after X-ray treatment. However, the presence of residual DjPiwi-1 transcription suggests that, although the majority of DjPiwi-1-positive cells can be neoblasts, this gene is also expressed in differentiating/differentiated cells. During regeneration DjPiwi-1-positive cells reorganize along the midline of the stump and no accumulation of hybridization signal was observed either in the blastema area or in the parenchymal region beneath the blastema. DjPiwi-1-positive cells, as well as the DjMCM2-expressing neoblasts located along the midline and those spread all over the parenchyma, showed a lower tolerance to X-ray with respect to the DjMCM2-expressing neoblasts distributed along the lateral lines of the parenchyma. Taken together, these findings suggest the presence of different neoblast subpopulations in planarians.

DjPum, a homologue of Drosophila Pumilio, is essential to planarian stem cell maintenance.

As stem cells are rare and difficult to study in vivo in adults, the use of classical models of regeneration to address fundamental aspects of the stem cell biology is emerging. Planarian regeneration, which is based upon totipotent stem cells present in the adult--the so-called neoblasts--provides a unique opportunity to study in vivo the molecular program that defines a stem cell. The choice of a stem cell to self-renew or differentiate involves regulatory molecules that also operate as translational repressors, such as members of PUF proteins. In this study, we identified a homologue of the Drosophila PUF gene Pumilio (DjPum) in the planarian Dugesia japonica, with an expression pattern preferentially restricted to neoblasts. Through RNA interference (RNAi), we demonstrate that gene silencing of DjPum dramatically reduces the number of neoblasts, thus supporting the intriguing hypothesis that stem cell maintenance may be an ancestral function of PUF proteins.

Djeyes absent (Djeya) controls prototypic planarian eye regeneration by cooperating with the transcription factor Djsix-1.

A conserved network of nuclear proteins is crucial to eye formation in both vertebrates and invertebrates. The finding that freshwater planarians can regenerate eyes without the contribution of Pax6 suggests that alternative combinations of regulatory elements may control the morphogenesis of the prototypic planarian eye. To further dissect the molecular events controlling eye regeneration in planarians, we investigated the role of eyes absent (Djeya) and six-1 (Djsix-1) genes in Dugesia japonica. These genes are expressed in both regenerating eyes and in differentiated photoreceptors of intact adults. Through RNAi studies, we show that Djsix-1 and Djeya are both critical for the regeneration of normal eyes in planarians and genetically cooperate in vivo to establish correct eye cell differentiation. We further demonstrate that the genetic interaction is mediated by physical interaction between the evolutionarily conserved domains of these two proteins. These data indicate that planarians use cooperatively Djsix-1 and Djeya for the proper specification of photoreceptors, implicating that the mechanism involving their evolutionarily conserved domains can be very ancient. Finally, both Djsix-1 and Djeya double-stranded RNA are substantially more effective at producing no-eye phenotypes in the second round of regeneration. This is probably due to the significant plasticity of the planarian model system, based on the presence of a stable population of totipotent stem cells, which ensure the rapid cell turnover of all differentiated cell types.

Expression of DjXnp, a novel member of the SNF2-like ATP-dependent chromatin remodelling genes, in intact and regenerating planarians.

SWI/SNF-related complexes include proteins implicated in the regulation of gene expression by chromatin remodelling. We have identified in planarians, invertebrates well-known for their regenerative capability,the cDNA of a novel gene, DjXnp, which encodes a protein of 1,076 amino acids, containing seven helicase domains similar to those found in the SNF2-like family members. Sequence comparison reveals a significant degree of similarity of DjXNP with mammalian XNP/ATRX proteins. In situ hybridization experiments performed on intact and regenerating planarians demonstrated that DjXnp transcripts were distributed in mesenchymal cells and were especially abundant in nerve cells. During anterior regeneration, DjXnp was detected in the blastemal area where the nervous system is newly forming. This expression pattern reveals extensive similarities with that described for mammalian XNP/ATRX, suggesting that these genes may have a conserved function at the cellular level.

The genetic network of prototypic planarian eye regeneration is Pax6 independent.

We report the presence of two Pax6-related genes, Pax6A and Pax6B, which are highly conserved in two planarian species Dugesia japonica and Girardia tigrina (Platyhelminthes, Tricladida). Pax6A is more similar to other Pax6 proteins than Pax6B, which is the most divergent Pax6 described so far. The planarian Pax6 homologs do not show any clear orthology to the Drosophila duplicated Pax6 genes, eyeless and twin of eyeless, which suggests an independent Pax6 duplication in a triclad or platyhelminth ancestor. Pax6A is expressed in the central nervous system of intact planarians, labeling a subset of cells of both cephalic ganglia and nerve cords, and is activated during cephalic regeneration. Pax6B follows a similar pattern, but shows a lower level of expression. Pax6A and Pax6B transcripts are detected in visual cells only at the ultrastructural level, probably because a limited amount of transcripts is present in these cells. Inactivation of both Pax6A and Pax6B by RNA-mediated gene interference (RNAi) inhibits neither eye regeneration nor eye maintenance, suggesting that the genetic network that controls this process is not triggered by Pax6 in planarians.

Characterization of DeY1, a novel Y-box gene specifically expressed in differentiating male germ cells of planarians.

Y-box proteins are conserved regulatory factors that play a key role in coordinating gene activity with protein synthesis by influencing both the transcription and translation of specific subsets of genes. We report the identification of a novel Y-box gene, DeY1, whose transcripts are found in the testes of sexual planarians. DeY1 is expressed in spermatogonia, spermatocytes and spermatids, while no expression is detected in spermatozoa. No DeY1 transcripts are found in the blastema during regeneration. The subcellular distribution of DeY1 protein was analyzed by electron microscope immunocytochemistry. Immunolabelling was found in the nucleus of spermatogonia, in both the nucleus and the cytoplasm of spermatocytes, and in the cytoplasm of spermatids.