Molecular impact of launch related dynamic vibrations and static hypergravity in planarians.

Although many examples of simulated and real microgravity demonstrating their profound effect on biological systems are described in literature, few reports deal with hypergravity and vibration effects, the levels of which are severely increased during the launch preceding the desired microgravity period. Here, we used planarians, flatworms that can regenerate any body part in a few days. Planarians are an ideal model to study the impact of launch-related hypergravity and vibration during a regenerative process in a "whole animal" context. Therefore, planarians were subjected to 8.5 minutes of 4 g hypergravity (i.e. a human-rated launch level) in the Large Diameter Centrifuge (LDC) and/or to vibrations (20-2000 Hz, 11.3 Grms) simulating the conditions of a standard rocket launch. The transcriptional levels of genes (erg-1, runt-1, fos, jnk, and yki) related with the early stress response were quantified through qPCR. The results show that early response genes are severely deregulated after static and dynamic loads but more so after a combined exposure of dynamic (vibration) and static (hypergravity) loads, more closely simulating real launch exposure profiles. Importantly, at least four days after the exposure, the transcriptional levels of those genes are still deregulated. Our results highlight the deep impact that short exposures to hypergravity and vibration have in organisms, and thus the implications that space flight launch could have. These phenomena should be taken into account when planning for well-controlled microgravity studies.

Tissue transplantation in planarians: A useful tool for molecular analysis of pattern formation.

Freshwater planarians are well known for their remarkable plasticity and regenerative capabilities. Most studies of planarian regeneration have specifically examined regeneration after transverse or longitudinal sectioning or during homeostasis in intact adults. However, tissue transplantation, first performed over a century ago, constitutes another important tool in the study of regeneration in planarians, and can be easily performed given this species' extraordinary healing capacity and its lack of a circulatory system. Studies conducted to date have demonstrated the viability of transplantations involving a variety of tissue types of different positional identities, affecting any of the 3 main body axes. Moreover, these grafting experiments have shown that tissues possess axial positional identities, which are retained following transplantation. The confrontation between different positional identities that occurs after any type of tissue transplantation is resolved by the formation of a blastema, consisting of undifferentiated tissue produced by adult pluripotent stem cells (neoblasts). This blastema intercalates the positional identities of the graft and host tissues. The recent discovery of pathways involved in planarian growth, patterning, and organogenesis, as well as corresponding molecular markers, makes tissue transplantation a vital new tool with which to explore pattern formation. Here, we discuss the different grafting approaches used in planarians, and the corresponding intercalary regenerative response, placing particular emphasis on the respective contributions of donor and host tissue. Moreover, we discuss the temporal induction of blastema formation, and present new molecular data on the generation of an ectopic anterior/posterior axis in response to dorsal/ventral confrontations between host and donor tissue.

Hippo signaling controls cell cycle and restricts cell plasticity in planarians.

The Hippo pathway plays a key role in regulating cell turnover in adult tissues, and abnormalities in this pathway are consistently associated with human cancers. Hippo was initially implicated in the control of cell proliferation and death, and its inhibition is linked to the expansion of stem cells and progenitors, leading to larger organ size and tumor formation. To understand the mechanism by which Hippo directs cell renewal and promotes stemness, we studied its function in planarians. These stem cell-based organisms are ideal models for the analysis of the complex cellular events underlying tissue renewal in the whole organism. hippo RNA interference (RNAi) in planarians decreased apoptotic cell death, induced cell cycle arrest, and could promote the dedifferentiation of postmitotic cells. hippo RNAi resulted in extensive undifferentiated areas and overgrowths, with no effect on body size or cell number. We propose an essential role for hippo in controlling cell cycle, restricting cell plasticity, and thereby preventing tumoral transformation.

Digital gene expression approach over multiple RNA-Seq data sets to detect neoblast transcriptional changes in Schmidtea mediterranea.

BACKGROUND: The freshwater planarian Schmidtea mediterranea is recognised as a valuable model for research into adult stem cells and regeneration. With the advent of the high-throughput sequencing technologies, it has become feasible to undertake detailed transcriptional analysis of its unique stem cell population, the neoblasts. Nonetheless, a reliable reference for this type of studies is still lacking. RESULTS: Taking advantage of digital gene expression (DGE) sequencing technology we compare all the available transcriptomes for S. mediterranea and improve their annotation. These results are accessible via web for the community of researchers. Using the quantitative nature of DGE, we describe the transcriptional profile of neoblasts and present 42 new neoblast genes, including several cancer-related genes and transcription factors. Furthermore, we describe in detail the Smed-meis-like gene and the three Nuclear Factor Y subunits Smed-nf-YA, Smed-nf-YB-2 and Smed-nf-YC. CONCLUSIONS: DGE is a valuable tool for gene discovery, quantification and annotation. The application of DGE in S. mediterranea confirms the planarian stem cells or neoblasts as a complex population of pluripotent and multipotent cells regulated by a mixture of transcription factors and cancer-related genes.