A new human embryonic cell type associated with activity of young transposable elements allows definition of the inner cell mass.

There remains much that we do not understand about the earliest stages of human development. On a gross level, there is evidence for apoptosis, but the nature of the affected cell types is unknown. Perhaps most importantly, the inner cell mass (ICM), from which the foetus is derived and hence of interest in reproductive health and regenerative medicine, has proven hard to define. Here, we provide a multi-method analysis of the early human embryo to resolve these issues. Single-cell analysis (on multiple independent datasets), supported by embryo visualisation, uncovers a common previously uncharacterised class of cells lacking commitment markers that segregates after embryonic gene activation (EGA) and shortly after undergo apoptosis. The discovery of this cell type allows us to clearly define their viable ontogenetic sisters, these being the cells of the ICM. While ICM is characterised by the activity of an Old non-transposing endogenous retrovirus (HERVH) that acts to suppress Young transposable elements, the new cell type, by contrast, expresses transpositionally competent Young elements and DNA-damage response genes. As the Young elements are RetroElements and the cells are excluded from the developmental process, we dub these REject cells. With these and ICM being characterised by differential mobile element activities, the human embryo may be a "selection arena" in which one group of cells selectively die, while other less damaged cells persist.

[18F]fluorodeoxyglucose-positron emission tomography and glucose-transporter type 1 expression in untreated primary small bowel adenocarcinoma.

BACKGROUND: Literature reporting [18F]fluorodexoyglucose positron emission tomography (FDG-PET) of small bowel adenocarcinoma, a rare tumor, is sparse. To assess FDG uptake in small bowel adenocarcinoma, we retrospectively analyzed a large, single-center database and determined the expression of glucose-transporter type 1 (GLUT-1). METHODS: Screening of PET datasets in the database (N.=28,961 scans) for untreated histologically-confirmed primary small bowel adenocarcinoma revealed evaluable PET datasets for eight patients. Maximum and peak standardized uptake values (SUVmax and SUVpeak, respectively) were calculated via volume-of-interest (VOI) analysis. Additionally, GLUT-1 expression on tumor specimens was prospectively immunohistochemically assessed. RESULTS: All primary tumors showed high FDG uptake: mean SUVmax was 9.5±2.6 (range: 5.0-13.0) and SUVpeak, 8.1±2.3 (range: 3.9-10.7). Corresponding biopsy specimens (N.=7) demonstrated high GLUT-1 expression. CONCLUSIONS: Primary small bowel adenocarcinomas have a high GLUT-1 expression. Tumor lesions consistently demonstrated high FDG uptake pre-treatment, suggesting FDG-PET utility in staging and follow-up of these tumors.

Engineered LINE-1 retrotransposition in nondividing human neurons.

Half the human genome is made of transposable elements (TEs), whose ongoing activity continues to impact our genome. LINE-1 (or L1) is an autonomous non-LTR retrotransposon in the human genome, comprising 17% of its genomic mass and containing an average of 80-100 active L1s per average genome that provide a source of inter-individual variation. New LINE-1 insertions are thought to accumulate mostly during human embryogenesis. Surprisingly, the activity of L1s can further impact the somatic human brain genome. However, it is currently unknown whether L1 can retrotranspose in other somatic healthy tissues or if L1 mobilization is restricted to neuronal precursor cells (NPCs) in the human brain. Here, we took advantage of an engineered L1 retrotransposition assay to analyze L1 mobilization rates in human mesenchymal (MSCs) and hematopoietic (HSCs) somatic stem cells. Notably, we have observed that L1 expression and engineered retrotransposition is much lower in both MSCs and HSCs when compared to NPCs. Remarkably, we have further demonstrated for the first time that engineered L1s can retrotranspose efficiently in mature nondividing neuronal cells. Thus, these findings suggest that the degree of somatic mosaicism and the impact of L1 retrotransposition in the human brain is likely much higher than previously thought.

The impact of transposable elements on mammalian development.

Despite often being classified as selfish or junk DNA, transposable elements (TEs) are a group of abundant genetic sequences that have a significant impact on mammalian development and genome regulation. In recent years, our understanding of how pre-existing TEs affect genome architecture, gene regulatory networks and protein function during mammalian embryogenesis has dramatically expanded. In addition, the mobilization of active TEs in selected cell types has been shown to generate genetic variation during development and in fully differentiated tissues. Importantly, the ongoing domestication and evolution of TEs appears to provide a rich source of regulatory elements, functional modules and genetic variation that fuels the evolution of mammalian developmental processes. Here, we review the functional impact that TEs exert on mammalian developmental processes and discuss how the somatic activity of TEs can influence gene regulatory networks.

LC-MS/MS based 25(OH)D status in a large Southern European outpatient cohort: gender- and age-specific differences.

BACKGROUND: Developed countries have a high prevalence of vitamin D deficiency. In previous studies, 25(OH)D was predominantly measured by immunoassays. The present study assessed serum 25(OH)D in a very large Southern European outpatient cohort by liquid chromatography tandem mass spectrometry (LC-MS/MS). MATERIALS AND METHODS: 74,235 serum 25(OH)D results generated under routine conditions between 2015 and 2016 were extracted from the laboratory information system of the Department of Clinical Pathology at Bolzano Hospital (Italy). In 3801 cases, parathyroid hormone (PTH) was requested in parallel. Serum 25(OH)D was measured by a NIST-972 aligned commercial LC-MS/MS method. The distribution of serum 25(OH)D concentrations in males and females of different age groups, the prevalence of 25(OH)D2 and seasonal variability were studied. RESULTS: The average 25(OH)D concentration in the entire cohort was 68.6 nmol/L (7.5-1880 nmol/L). Females had a 7 nmol/L higher average 25(OH)D concentration than males, which increased significantly with age. 37.9 and 28.3% of males and females, respectively, had a deficient 25(OH)D concentration of < 50 nmol/L. 620 samples (0.84%) had measureable amounts of 25(OH)D2. In samples with a normal PTH, 25(OH)D was 11 nmol/L higher than in the entire cohort. Seasonal variation ranged between 20 and 30% and was most pronounced in young individuals. 25(OH)D2 remained constant throughout the year. CONCLUSION: Average serum 25(OH)D in South Tyrol is higher than in other parts of Europe. 25(OH)D and PTH show a continuous inverse relationship. Seasonal variation of serum 25(OH)D is an important aspect in young and middle-aged adults, but becomes less relevant in elderly subjects. 25(OH)D2 is of minor practical importance in South Tyrol.

Rapid reconstitution of CMV-specific T-cells after stem-cell transplantation.

OBJECTIVE: As reconstitution of virus-specific T-cells is critical to control cytomegalovirus (CMV)-viremia following stem-cell transplantation (SCT), we characterized the dynamics in CMV-specific T-cell reconstitution after SCT. METHODS: Cytomegalovirus-specific T-cells from 51 SCT-recipients were prospectively quantified and phenotypically characterised by intracellular cytokine-staining after specific stimulation and HLA class-I-specific pentamers using flow cytometry. RESULTS: Cytomegalovirus-specific CD4 T-cells reconstituted after a median of 2.3 (IQR, 2.0-3.0) weeks following autografting, and 4.0 (IQR, 3.0-5.6) weeks after allografting, with CMV-specific T-cells originating from donors and/or recipients. The time for reconstitution of CMV-specific CD4 and CD8 T-cells did not differ (P = .58). Factors delaying the time to initial reconstitution of CMV-specific CD4 T-cells included a negative recipient serostatus (P = .016) and CMV-viremia (P = .026). Percentages of CMV-specific CD4 T-cells significantly increased over time and reached a plateau after 90 days (P = .043). Relative CMV-specific CD4 T-cell levels remained higher in long-term transplant recipients compared with those in controls (P < .0001). However, due to persisting lymphopenia, absolute numbers of CMV-specific T-cells were similar as in controls. CONCLUSION: Cytomegalovirus-specific T-cells rapidly reconstitute after SCT and their percentages remain high in the long term. In the face of persistent lymphopenia, this results in similar absolute numbers of CMV-specific T-cells as in controls to ensure sufficient pathogen control.

One-carbon metabolites and telomere length in a prospective and randomized study of B- and/or D-vitamin supplementation.

BACKGROUND: Vitamin B deficiency is common in elderly people and has been associated with an increased risk of developing age-related diseases. B-vitamins are essential for the synthesis and stability of DNA. Telomers are the end caps of chromosomes that shorten progressively with age, and short telomers are associated with DNA instability. OBJECTIVE: In the present randomized intervention study, we investigated whether the one-carbon metabolism is related to telomere length, a surrogate marker for cellular aging. DESIGN: Sixty-five subjects (>54 years) were randomly assigned to receive either a daily combination of vitamin D3 (1200 IU), folic acid (0.5 mg), vitamin B12 (0.5 mg), vitamin B6 (50 mg) and calcium carbonate (456 mg) (group A) or vitamin D3 and calcium carbonate alone (group B). Blood testing was performed at baseline and after 1 year of supplementation. The concentrations of several metabolites of the one-carbon pathway, as well as relative telomere length (RTL) and 5,10-methylenetetrahydrofolate reductase C677T genotype, were analyzed. RESULTS: At baseline, age- and gender-adjusted RTL correlated with total folate and 5-methyltetrahydrofolate (5-methylTHF). Subjects with RTL above the median had higher concentrations of total folate and 5-methylTHF compared to subjects below the median. At study end, gender- and age-adjusted RTL correlated in group A with methylmalonic acid (MMA; r = -0.460, p = 0.0012) and choline (r = 0.434, p = 0.0021) and in group B with 5,10-methenyltetrahydrofolate (r = 0.455, p = 0.026) and dimethylglycine (DMG; r = -0.386, p = 0.047). Subjects in the group A with RTL above the median had lower MMA and higher choline compared to subjects below the median. CONCLUSIONS: The present pilot study suggests a functional relationship between one-carbon metabolism and telomere length. This conclusion is supported by several correlations that were modified by B-vitamin supplementation. In agreement with our hypothesis, the availability of nucleotides and methylation groups seems to impact telomere length. Due to the small sample size and the limitations of the study, further studies should confirm the present results in a larger cohort.

EBV-transformed lymphoblastoid cell lines as vaccines against cancer testis antigen-positive tumors.

EBV-transformed lymphoblastoid cell lines (LCL) are potent antigen-presenting cells. To investigate their potential use as cancer testis antigen (CTA) vaccines, we studied the expression of 12 cancer testis (CT) genes in 20 LCL by RT-PCR. The most frequently expressed CT genes were SSX4 (50 %), followed by GAGE (45 %), SSX1 (40 %), MAGE-A3 and SSX2 (25 %), SCP1, HOM-TES-85, MAGE-C1, and MAGE-C2 (15 %). NY-ESO-1 and MAGE-A4 were found in 1/20 LCL and BORIS was not detected at all. Fifteen of 20 LCL expressed at least one antigen, 9 LCL expressed ≥2 CT genes, and 7 of the 20 LCL expressed ≥4 CT genes. The expression of CT genes did not correlate with the length of in vitro culture, telomerase activity, aneuploidy, or proliferation state. While spontaneous expression of CT genes determined by real-time PCR and Western blot was rather weak in most LCL, treatment with DNA methyltransferase 1 inhibitor alone or in combination with histone deacetylase inhibitors increased CTA expression considerably thus enabling LCL to induce CTA-specific T cell responses. The stability of the CT gene expression over prolonged culture periods makes LCL attractive candidates for CT vaccines both in hematological neoplasias and solid tumors.

Ratiometric Two-Photon Near-Infrared Probe to Detect DPP IV in Human Plasma, Living Cells, Human Tissues, and Whole Organisms Using Zebrafish.

DPP IV, otherwise known as CD26 lymphocyte T surface antigen, is a transmembrane glycoprotein also found in circulation in the blood. It plays an important role in several processes like glucose metabolism and T-cell stimulation. Moreover, it is overexpressed in renal, colon, prostate, and thyroid human carcinoma tissues. It can also serve as a diagnostic in patients with lysosomal storage diseases. The biological and clinical importance of having readouts for the activity of this enzyme, in physiological and disease conditions, has led us to design a near-infrared (NIR) fluorimetric probe that also has the characteristics of being ratiometric and excitable by two simultaneous NIR photons. The probe consists of assembling an enzyme recognition group (Gly-Pro) (Mentlein, 1999; Klemann et al., 2016) on the two-photon (TP) fluorophore (derivative of dicyanomethylene-4H-pyran, DCM-NH2) disturbing its NIR characteristic internal charge transfer (ICT) emission spectrum. When the dipeptide group is released by the DPP IV-specific enzymatic action, the donor-acceptor DCM-NH2 is restored, forming a system that shows high ratiometric fluorescence output. With this new probe, we have been able to detect, quickly and efficiently, the enzymatic activity of DPP IV in living cells, human tissues, and whole organisms, using zebrafish. In addition, due to the possibility of being excited by two photons, we can avoid the autofluorescence and subsequent photobleaching that the raw plasma has when it is excited by visible light, achieving detection of the activity of DPP IV in that medium without interference.

Integrins Cooperate With the EGFR/Ras Pathway to Preserve Epithelia Survival and Architecture in Development and Oncogenesis.

Adhesion to the extracellular matrix (ECM) is required for normal epithelial cell survival. Disruption of this interaction leads to a specific type of apoptosis known as anoikis. Yet, there are physiological and pathological situations in which cells not connected to the ECM are protected from anoikis, such as during cell migration or metastasis. The main receptors transmitting signals from the ECM are members of the integrin family. However, although integrin-mediated cell-ECM anchorage has been long recognized as crucial for epithelial cell survival, the in vivo significance of this interaction remains to be weighed. In this work, we have used the Drosophila wing imaginal disc epithelium to analyze the importance of integrins as survival factors during epithelia morphogenesis. We show that reducing integrin expression in the wing disc induces caspase-dependent cell death and basal extrusion of the dead cells. In this case, anoikis is mediated by the activation of the JNK pathway, which in turn triggers expression of the proapoptotic protein Hid. In addition, our results strongly suggest that, during wing disc morphogenesis, the EGFR pathway protects cells undergoing cell shape changes upon ECM detachment from anoikis. Furthermore, we show that oncogenic activation of the EGFR/Ras pathway in integrin mutant cells rescues them from apoptosis while promoting their extrusion from the epithelium. Altogether, our results support the idea that integrins promote cell survival during normal tissue morphogenesis and prevent the extrusion of transformed cells.

Wingless signaling and the control of cell shape in Drosophila wing imaginal discs.

The control of cell morphology is important for shaping animals during development. Here we address the role of the Wnt/Wingless signal transduction pathway and two of its target genes, vestigial and shotgun (encoding E-cadherin), in controlling the columnar shape of Drosophila wing disc cells. We show that clones of cells mutant for arrow (encoding an essential component of the Wingless signal transduction pathway), vestigial or shotgun undergo profound cell shape changes and are extruded towards the basal side of the epithelium. Compartment-wide expression of a dominant-negative form of the Wingless transducer T-cell factor (TCF/Pangolin), or double-stranded RNA targeting vestigial or shotgun, leads to abnormally short cells throughout this region, indicating that these genes act cell autonomously to maintain normal columnar cell shape. Conversely, overexpression of Wingless, a constitutively-active form of the Wingless transducer beta-catenin/Armadillo, or Vestigial, results in precocious cell elongation. Co-expression of Vestigial partially suppresses the abnormal cell shape induced by dominant-negative TCF. We conclude that Wingless signal transduction plays a cell-autonomous role in promoting and maintaining the columnar shape of wing disc cells. Furthermore, our data suggest that Wingless controls cell shape, in part, through maintaining vestigial expression.

Physical exercise prevents cellular senescence in circulating leukocytes and in the vessel wall.

BACKGROUND: The underlying molecular mechanisms of the vasculoprotective effects of physical exercise are incompletely understood. Telomere erosion is a central component of aging, and telomere-associated proteins regulate cellular senescence and survival. This study examines the effects of exercising on vascular telomere biology and endothelial apoptosis in mice and the effects of long-term endurance training on telomere biology in humans. METHODS AND RESULTS: C57/Bl6 mice were randomized to voluntary running or no running wheel conditions for 3 weeks. Exercise upregulated telomerase activity in the thoracic aorta and in circulating mononuclear cells compared with sedentary controls, increased vascular expression of telomere repeat-binding factor 2 and Ku70, and reduced the expression of vascular apoptosis regulators such as cell-cycle-checkpoint kinase 2, p16, and p53. Mice preconditioned by voluntary running exhibited a marked reduction in lipopolysaccharide-induced aortic endothelial apoptosis. Transgenic mouse studies showed that endothelial nitric oxide synthase and telomerase reverse transcriptase synergize to confer endothelial stress resistance after physical activity. To test the significance of these data in humans, telomere biology in circulating leukocytes of young and middle-aged track and field athletes was analyzed. Peripheral blood leukocytes isolated from endurance athletes showed increased telomerase activity, expression of telomere-stabilizing proteins, and downregulation of cell-cycle inhibitors compared with untrained individuals. Long-term endurance training was associated with reduced leukocyte telomere erosion compared with untrained controls. CONCLUSIONS: Physical activity regulates telomere-stabilizing proteins in mice and in humans and thereby protects from stress-induced vascular apoptosis.

Detection of Meningeosis neoplastica by real-time quantitation of telomerase activity.

BACKGROUND: Analysis of cerebrospinal fluid (CSF) to discriminate between benign and malignant conditions is of fundamental importance for the physician and the patient because of the differential therapeutic options and resulting morbidity and mortality. Most human tumours demonstrate increased telomerase activity (TA). Recent technical advances in the detection of TA allow for sensitive and specific detection within 4 h. Thus, the detection of TA is suitable for routine clinical testing. METHODS: This study examines TA in cellular proteins in CSF from 111 patients compared to cytomorphological and laboratory examination. RESULTS: A positive result for TA in cellular proteins of CSF was correlated significantly with Meningeosis neoplastica, but not with non-malignant conditions. Telomerase was not detected in CSF supernatant, despite positive results in cellular proteins from identical patients. Furthermore, a 48-h time delay during the pre-analytic processing is not critical for detection of TA detection in native CSF when stored at room temperature. CONCLUSIONS: We conclude that TA is a promising marker for the detection of Meningeosis neoplastica and warrants further study.

Sustained telomere erosion due to increased stem cell turnover during triple autologous hematopoietic stem cell transplantation.

Telomeres cap chromosomal ends and are shortened throughout a lifetime. Additional telomere erosion has been documented during conventional chemotherapy or hematopoietic stem cell transplantation. Previous studies of stem cell transplantation reported variable amounts of telomere shortening with inconsistent results regarding the persistence of telomere shortening. Here we have prospectively studied telomere length and proliferation kinetics of hematopoietic cells in aggressive non-Hodgkin lymphoma patients who underwent a four-course high-dose chemotherapy protocol combined with triple autologous stem cell transplantation. We observed sustained telomere shortening in hematopoietic cells after triple stem cell transplantation with prolonged stem cell replication during the first year after stem cell transplantation.

Short telomeres in aggressive non-Hodgkin's lymphoma as a risk factor in lymphomagenesis.

OBJECTIVE: Telomeres cap chromosomal ends and help to maintain chromosomal integrity. Telomere shortening may result in chromosomal instability and, ultimately, malignant transformation of cells. It has not been systematically studied whether patients with malignancy have shortened telomeres in their normal, nontransformed cells, which might point to a preexisting disposition for chromosomal instability. METHODS: We designed an (age-) matched pair analysis that compared telomere length in nonmalignant peripheral leukocytes from previously untreated patients who recently developed an aggressive non-Hodgkin's lymphoma, with leukocytes from healthy individuals. RESULTS: Telomere lengths in B and T lymphocytes as well as granulocytes from the patients' group were significantly shorter than those from age-matched healthy controls. We were able to rule out increased proliferation, telomerase defects, or increased oxidative stress in patients as confounding factors of shortened telomeres. CONCLUSION: Short telomeres in nontransformed leukocytes may constitute a risk factor for lymphomagenesis.

Stimulation of osteoclast activity by low B-vitamin concentrations.

BACKGROUND: Homocysteine (HCY) has recently been linked to fragility fractures. Moreover, HCY activates osteoclasts (OC). Elevated HCY concentrations are mainly caused by folate, vitamin B12 (B12) and B6 (B6) deficiencies. We hypothesized that folate, B12 and B6 deficiencies stimulate OC activity. MATERIALS AND METHODS: OC were cultured from peripheral blood mononuclear cells (10 healthy male donors, 34+/-5 years) for 20 days. Culture medium was conditioned with decreasing concentrations of folate, B12 and B6 (in combination or variation of only one vitamin) starting at physiologic concentrations. Moreover, we tested increasing concentrations of HCY. OC activity was measured by dentine resorption activity (DRA), tartrate-resistant acid phosphatase (TRAP) and cathepsin K (CK) activity. RESULTS: The combined reduction of folate, B12 and B6 stimulated DRA up to 211% (p<0.001). This observation was confirmed by TRAP (maximum increase 24%, p<0.001) and CK (maximum increase 24%, p<0.001). Reduction of only one vitamin stimulated DRA up to 250% (folate: maximum increase 248%, p<0.018; B12: maximum increase 252%, p<0.001, B6: maximum increase 247%, p<0.001). However, only for folate this effect could be confirmed by TRAP (maximum increase 33%, p<0.001). HCY stimulated DRA up to 395% (p<0.001). TRAP (maximum increase 49%, p<0.001) and CK analyses confirmed this observation (maximum increase 50%, p<0.001). CONCLUSION: Our results demonstrate a strong stimulatory effect of low concentrations of folate, B12 and B6 on OC activity, suggesting a mechanistic role of low B-vitamin concentrations for bone degradation. Consequently, OC stimulation by low folate, B12 and B6 concentrations could be an important adverse factor for bone health.

Accumulation of homocysteine by decreasing concentrations of folate, vitamin B12 and B6 does not influence the activity of human osteoblasts in vitro.

BACKGROUND: Homocysteine (HCY) has recently been linked to fragility fractures. Elevated circulating HCY is mainly caused by folate, vitamin B12 and B6 deficiencies. However, little is known about the effect of these vitamins on the activity of osteoblasts. We hypothesized that decreasing concentrations of folate, vitamin B12 and B6 decrease osteoblasts activity by accumulation of HCY. METHODS: Osteoblasts obtained from trabecular human bone specimens of 8 donors were cultured with decreasing concentrations of folate, vitamin B12 and B6. Vitamin concentrations were modified in combination or one vitamin only (8 repetitions x 8 donors, n=64). After 14 days alkaline phosphatase (AP) activity, pro-collagen type I N-terminal peptide (PINP) and osteocalcin secretion in the supernatant was measured. After 20 days, the formation of mineralized matrix was analyzed. RESULTS: Decreasing B-vitamin concentrations induced a significant accumulation of HCY in the supernatant reaching up to 160%. The increase in HCY was not accompanied by changes of AP, osteocalcin and PINP. Moreover, mineralized matrix formation was not affected. CONCLUSION: Accumulation of HCY by decreasing concentrations of folate, vitamin B12 and B6 does not affect the activity of human osteoblasts. Consequently, other mechanisms have to be responsible for the reduced bone quality in hyperhomocysteinemic subjects.

Influence of telomere length on short-term recovery after allogeneic stem cell transplantation.

OBJECTIVE: Telomeres shorten in somatic cells during aging and states of increased turnover, including hematopoietic stem cell transplantation. Fast hematopoietic recovery is critical for the patients' course after hematopoietic stem cell transplantation. It is unknown whether telomere length in hematopoietic stem cells (HSCs) predicts short-term hematopoietic recovery. METHODS: We quantified telomere length by flow fluorescence in situ hybridization analysis in HSCs and granulocytes of healthy stem cell donors and monitored time to peripheral blood cell recovery in transplanted hosts. Furthermore, we measured in vitro repopulation potency of HSCs by assaying for colony-forming units granulocyte-macrophage (CFU-GM). RESULTS: Telomere length in HSC shortens continuously in vivo and is comparable to telomere length in granulocytes from the same individual. Numbers of in vitro formed CFU-GM per HSC show an inverse relationship to age and telomere length. However, telomere length in HSCs was not correlated with short-term recovery after HSC transplantation. CONCLUSION: These findings suggest that healthy stem cell donors have sufficient telomere length reserve to repopulate a myeloablatively treated host, despite continuous aging of HSCs in vivo and decreased repopulation ability of HSCs from older donors in vitro.

Physical mechanisms shaping the Drosophila dorsoventral compartment boundary.

BACKGROUND: Separating cells with distinct identities and fates by straight and sharp compartment boundaries is important for growth and pattern formation during animal development. The physical mechanisms shaping compartment boundaries, however, are not fully understood. RESULTS: We combine theory and quantitative experiments to investigate the roles of different mechanisms to shape compartment boundaries. Our theoretical work shows that cell elongation created by anisotropic stress, cell proliferation rate, orientation of cell division, and cell bond tension all have distinct effects on the morphology of compartment boundaries during tissue growth. Our experiments using the developing Drosophila wing reveal that the roughness of the dorsoventral compartment boundary is dynamic and that it decreases during development. By measuring tissue relaxation in response to laser ablation of cell bonds at different developmental times, we demonstrate that decreased boundary roughness correlates with increased cell bond tension along the compartment boundary. Finally, by using experimentally determined values for cell bond tension, cell elongation and bias in orientation of cell division in simulations of tissue growth, we can reproduce the main features of the time evolution of the dorsoventral compartment boundary shape. CONCLUSIONS: Local increase of cell bond tension along the boundary as well as global anisotropies in the tissue contribute to shaping boundaries in cell networks. We propose a simple scenario that combines time-dependent cell bond tension at the boundary, oriented cell division, and cell elongation in the tissue that can account for the main features of the dynamics of the shape of the dorsoventral compartment boundary.