Cellular fate decisions are influenced by their topographical location in the adult body. For instance, tissue repair and neoplastic growth are greater in anterior than in posterior regions of adult animals. However, the molecular underpinnings of these regional differences are unknown. We identified a regional switch in the adult planarian body upon systemic disruption of homologous recombination with RNAinterference of Rad51. Rad51 knockdown increases DNA doublestrand breaks (DSBs) throughout the body, but stem cells react differently depending on their location along the anteroposterior axis. In the presence of extensive DSBs, cells in the anterior part of the body resist death, whereas cells in the posterior region undergo apoptosis. Furthermore, we found that proliferation of cells with DNA damage is induced in the presence of brain tissue and that the retinoblastoma pathway enables overproliferation of cells with DSBs while attending to the demands of tissue growth and repair. Our results implicate both autonomous and non-autonomous mechanisms as key mediators of regional cell behavior and cellular transformation in the adult body.

SummaryTarget of Rapamycin (TOR) controls an evolutionarily conserved signaling pathway that modulates cellular growth and division by sensing levels of nutrients, energy and stress. As such, TOR signaling is a crucial component of tissues and organs that translates systemic signals into cellular behavior. The ubiquitous nature of TOR signaling, together with the difficulty of analyzing tissue during cellular turnover and repair, have limited our understanding of how this kinase operates throughout the body. Here, we use the planarian model system to address TOR regulation at the organismal level. The planarian TOR homolog (Smed-TOR) is ubiquitously expressed, including stem cells (neoblasts) and differentiated tissues. Inhibition of TOR with RNA interference severely restricts cell proliferation, allowing the study of neoblasts with restricted proliferative capacity during regeneration and systemic cell turnover. Strikingly, TOR signaling is required for neoblast response to amputation and localized growth (blastema). However, in the absence of TOR signaling, regeneration takes place only within differentiated tissues. In addition, TOR is essential for maintaining the balance between cell division and cell death, and its dysfunction leads to tissue degeneration and lack of organismal growth in the presence of nutrients. Finally, TOR function is likely to be mediated through TOR Complex 1 as its disruption recapitulates signs of the TOR phenotype. Our data reveal novel roles for TOR signaling in controlling adult stem cells at a systemic level and suggest a new paradigm for studying TOR function during physiological turnover and regeneration.

SUMMARY Reactive α-dicarbonyls (α-DCs), like methylglyoxal (MGO) accumulate with age, and have been implicated in aging and various age-associated pathologies such as diabetic complications and neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. Evolutionarily conserved glyoxalases are responsible for α-DC detoxification; however their core biochemical regulation have remained unclear. We have established a Caenorhabditis elegans model, based on an impaired glyoxalase (glod-4/GLO1), to broadly study α-DC-related stress. We show that in comparison to wild-type (N2, Bristol), glod-4 animals rapidly exhibit several pathogenic phenotypes including hyperesthesia, neuronal damage, reduced motility, and early mortality. We further demonstrate TRPA-1/TRPA1 as a sensor for α-DCs, conserved between worms and mammals. Moreover, TRPA-1 activates SKN-1/Nrf via calcium-modulated kinase signaling, ultimately regulating the glutathione-dependent (GLO1) and co-factor-independent (DJ1) glyoxalases to detoxify α-DCs. Interestingly, this pathway is in stark contrast to the TRPA-1 activation and the ensuing calcium flux implicated in cold sensation in C. elegans, whereby DAF-16/FOXO gets activated via complementary kinase signaling. Finally, a phenotypic drug-screen using C. elegans identified podocarpic acid as a novel activator of TRPA1 that rescues α-DC-induced pathologies in C. elegans and mammalian cells. Our work thus identifies TRPA1 as a bonafide drug target for amelioration of α-DC stress, which represents a viable option to address aging-related pathologies in diabetes and neurodegenerative diseases.

The immune system has been implicated as an important modulator of tissue regeneration. However, the mechanisms driving injury-induced immune response and tissue repair remain poorly understood. For over 200 years, planarians have been a classical model for studies on tissue regeneration, but the planarian immune system and its potential role in repair is largely unknown. We found through comparative genomic analysis and data mining that planarians contain many potential homologs of the innate immune system that are activated during injury and repair of adult tissues. These findings support the notion that the relationship between adult tissue repair and the immune system is an ancient feature of basal Bilateria. Further analysis of the planarian immune system during regeneration could potentially add to our understanding of how the innate immune system and inflammatory responses interplay with regenerative signals to induce scar-less tissue repair in the context of the adult organism.

CCAAT enhancer-binding protein ␤ (C͞EBP␤), a basic-leucine zipper transcription factor, is an important effector of signals in physiologic growth and cancer. The identification of direct C͞EBP␤ targets in vivo has been limited by functional compensation by other C͞EBP family proteins and the low stringency of the consensus sequence. Here we use the combined power of expression profiling and high-throughput chromatin immunoprecipitation to identify direct and biologically relevant targets of C͞EBP␤. We identified 25 potential C͞EBP␤ targets, of which 88% of those tested were confirmed as in vivo C͞EBP␤-binding sites. Six of these genes also displayed differential expression in C͞EBP␤ ؊/؊ livers. Computational analysis revealed that bona fide C͞EBP␤ target genes can be distinguished by the presence of binding motifs for specific additional transcription factors in the vicinity of the C͞EBP␤ site. This approach is generally applicable to the discovery of direct, biologically relevant targets of mammalian transcription factors.C CAAT enhancer-binding proteins (C͞EBPs) constitute a family of basic-leucine zipper (bZIP) transcription factors that are critical for the regulation of numerous biological processes, including differentiation, metabolic homeostasis, proliferation, tumorigenesis, inflammation, and apoptosis (1-9). C͞EBP proteins are regulated at multiple levels, including gene transcription, translation, and phosphorylation, in response to a variety of stimuli including hormonal, cytokine and growth factor-signaling pathways (1). C͞EBP proteins are able to form hetero-and homodimeric complexes with other C͞EBP family members, thereby creating additional diversity in target sequence recognition.C͞EBP␤ is an important effector of growth signals in experimental models of physiologic and neoplastic growth, the acutephase response, and metabolic homeostasis (1-11). Livers from C͞EBP␤ Ϫ/Ϫ mice exhibit a blunted regenerative response associated with prolonged hypoglycemia and altered expression of several cell-cycle-associated genes (10). In addition, a recent microarray analysis of human tumors has implicated C͞EBP␤ as a downstream mediator of cyclin D (12). Although these studies provide strong support for the role of C͞EBP␤ as a regulator of cell growth, at present, neither the mechanism by which C͞EBP␤ modulates the growth effects of cyclin D1 nor the targets of C͞EBP␤ in this pathway have been elucidated.A variety of approaches has been used to identify C͞EBP␤-binding sites, including cell culture systems, C͞EBP␤ Ϫ/Ϫ mice, and analyses of promoter sequences. However, several obstacles have limited the identification of direct C͞EBP␤-dependent transcriptional targets in vivo. All C͞EBP family members with the exception of C͞EBP possess identical in vitro DNA-binding affinity for C͞EBP consensus sequences, suggesting that other C͞EBP family members may be able to compensate for the loss of C͞EBP␤ (13). Second, the application of computational sequence analysis to identify C͞EBP promoter sequences has been impede...