Sahar Nissim

Evidence for an expansion-based temporal Shh gradient in specifying vertebrate digit identities.

The zone of polarizing activity (ZPA) in the posterior limb bud produces Sonic Hedgehog (Shh) protein, which plays a critical role in establishing distinct fates along the anterior-posterior axis. This activity has been modeled as a concentration-dependent response to a diffusible morphogen. Using recombinase base mapping in the mouse, we determine the ultimate fate of the Shh-producing cells. Strikingly, the descendants of the Shh-producing cells encompass all cells in the two most posterior digits and also contribute to the middle digit. Our analysis suggests that, while specification of the anterior digits depends upon differential concentrations of Shh, the length of time of exposure to Shh is critical in the specification of the differences between the most posterior digits. Genetic studies of the effects of limiting accessibility of Shh within the limb support this model, in which the effect of the Shh morphogen is dictated by a temporal as well as a spatial gradient.

Tbx5 is required for forelimb bud formation and continued outgrowth

Tbx5 is a T-box transcription factor expressed exclusively in the developing forelimb but not in the developing hindlimb of vertebrates. Tbx5 is first detected in the prospective forelimb mesenchyme prior to overt limb bud outgrowth and its expression is maintained throughout later limb development stages. Direct evidence for a role of Tbx5 in forelimb development was provided by the discovery that mutations in human TBX5 cause Holt-Oram Syndrome (HOS), a dominant disorder characterised predominantly by upper(fore) limb defects and heart abnormalities. Misexpression studies in the chick have demonstrated a role for this gene in limb-type specification. Using a conditional knockout strategy in the mouse to delete Tbx5 gene function in the developing forelimb, we demonstrate that this gene is also required at early limb bud stages for forelimb bud development. In addition, by misexpressing dominant-negative and dominant-activated forms of Tbx5 in the chick wing we provide evidence that this gene is also required at later stages of limb bud development for continued limb outgrowth. Our results provide a context to understand the defects observed in HOS caused by haploinsufficiency of TBX5 in human. Moreover, our results also demonstrate that limb bud outgrowth and specification of limb identity are linked by a requirement for Tbx5.

Ferritinophagy via NCOA4 is required for erythropoiesis and is regulated by iron dependent HERC2-mediated proteolysis

NCOA4 is a selective cargo receptor for the autophagic turnover of ferritin, a process critical for regulation of intracellular iron bioavailability. However, how ferritinophagy flux is controlled and the roles of NCOA4 in iron-dependent processes are poorly understood. Through analysis of the NCOA4-FTH1 interaction, we demonstrate that direct association via a key surface arginine in FTH1 and a C-terminal element in NCOA4 is required for delivery of ferritin to the lysosome via autophagosomes. Moreover, NCOA4 abundance is under dual control via autophagy and the ubiquitin proteasome system. Ubiquitin-dependent NCOA4 turnover is promoted by excess iron and involves an iron-dependent interaction between NCOA4 and the HERC2 ubiquitin ligase. In zebrafish and cultured cells, NCOA4 plays an essential role in erythroid differentiation. This work reveals the molecular nature of the NCOA4-ferritin complex and explains how intracellular iron levels modulate NCOA4-mediated ferritinophagy in cells and in an iron-dependent physiological setting. DOI: http://dx.doi.org/10.7554/eLife.10308.001

Genetic markers of malignant transformation in intraductal papillary mucinous neoplasm of the pancreas: a meta-analysis.

Objectives The objective of this study was to determine the relationship between specific genetic alterations and malignant transformation in intraductal papillary mucinous neoplasm (IPMN) of the pancreas. Methods Quantitative meta-analysis was conducted of studies through October 2010 that adhered to the 1996 World Health Organization guidelines for distinguishing adenoma and borderline IPMN versus carcinoma in surgically resected specimens using a random-effects model. We developed a 6-point scoring system to assess study quality. Results Thirty-nine studies (1235 IPMN samples) satisfied the inclusion criteria, and we conducted pooled analysis of 8 genetic markers: MUC1, MUC2, MUC5AC, kRas, p53, hTERT (human telomerase reverse transcriptase), cyclooxygenase 2, and Shh (Sonic hedgehog). Markers having the strongest association with malignant IPMN were hTERT (odds ratio [OR], 11.4; 95% confidence interval [CI], 3.5–36.7) and Shh (OR, 6.9; 95% CI, 2.4–20.2), whereas MUC5AC (OR, 1.0; 95% CI, 0.1–13.9) and kRas (OR, 2.0; 95% CI, 1.0–4.3) showed weak association with IPMN histologic progression. Conclusions Expression of hTERT is strongly associated with malignant transformation in IPMN, consistent with up-regulation of hTERT as a key step in progression of IPMN to cancer. Expression of kRas and MUC5AC is common but not strongly associated with IPMN histologic progression. The quality criteria used here may guide future reporting of genetic markers related to malignant transformation of IPMN.

Estrogen Defines the Dorsal-Ventral Limit of VEGF Regulation to Specify the Location of the Hemogenic Endothelial Niche

Genetic control of hematopoietic stem and progenitor cell (HSPC) function is increasingly understood; however, less is known about the interactions specifying the embryonic hematopoietic niche. Here, we report that 17β-estradiol (E2) influences production of runx1+ HSPCs in the AGM region by antagonizing VEGF signaling and subsequent assignment of hemogenic endothelial (HE) identity. Exposure to exogenous E2 during vascular niche development significantly disrupted flk1+ vessel maturation, ephrinB2+ arterial identity, and specification of scl+ HE by decreasing expression of VEGFAa and downstream arterial Notch-pathway components; heat shock induction of VEGFAa/Notch rescued E2-mediated hematovascular defects. Conversely, repression of endogenous E2 activity increased somitic VEGF expression and vascular target regulation, shifting assignment of arterial/venous fate and HE localization; blocking E2 signaling allowed venous production of scl+/runx1+ cells, independent of arterial identity acquisition. Together, these data suggest that yolk-derived E2 sets the ventral boundary of hemogenic vascular niche specification by antagonizing the dorsal-ventral regulatory limits of VEGF.

Neural Stem Cells for Cns Repair: State of the Art and Future Directions

The ferning test of tears has been an intensively discussed method for rough but quick visualization of general tear fluid composition. Regarded as crystallization process resulting from simple water subtraction (Battaglia and Giusto 1993), it has useful features, amongst them the minimal equipment required, but standardization is a known problem. The classification according to Rolando (1984) seems to significantly increase the clinical applicability of this technique (Pensyl and Dillehay 1998). Even though the ferning test has been proposed for predicting contact lens tolerance (Ravazzoni et al. 1998), the underlying mechanisms of the ferning pattern is still not clearly understood (Kogbe et al. 1991). Recently, it has been evaluated as a method to develop a rough picture of the crystallization process, reflecting the qualitative composition of tears (Sommer et al. 1994). The accuracy of the method, however, in clinical conditions such as dry eyes seems to be inferior to impression cytology (Jackson and Perrigin 1999), but it may show clear pathological changes (Norn 1994, Vaikoussis et al. 1994, Maragou et al. 1996). Today, with the current means of interpretation, the ferning test is seen as a practical, quick, easy and reliable complement to other tests (Albach et al. 1994). In the present study we develop a further use of the ferning procedure.

Selenoprotein H is an essential regulator of redox homeostasis that cooperates with p53 in development and tumorigenesis

Significance Dietary selenium and selenoproteins play important roles in regulating redox processes that impact human health. The human genome includes 25 genes for selenoproteins, which have diverse roles in redox homeostasis, thyroid hormone metabolism, endoplasmic reticulum quality control, selenium transport, and other functions. Selenoprotein H (seph) is a recently identified nucleolar oxidoreductase with DNA-binding properties whose function is not well understood. In this work, we used a unique combination of unbiased metabolomic and transcriptomic approaches in zebrafish to discover that seph is an essential regulator of redox homeostasis that regulates p53. In addition, we demonstrate the seph-deficient adults are prone to chemically induced carcinogenesis. Our results suggest that seph suppresses oxidative stress and DNA damage in the nucleolus. Selenium, an essential micronutrient known for its cancer prevention properties, is incorporated into a class of selenocysteine-containing proteins (selenoproteins). Selenoprotein H (SepH) is a recently identified nucleolar oxidoreductase whose function is not well understood. Here we report that seph is an essential gene regulating organ development in zebrafish. Metabolite profiling by targeted LC-MS/MS demonstrated that SepH deficiency impairs redox balance by reducing the levels of ascorbate and methionine, while increasing methionine sulfoxide. Transcriptome analysis revealed that SepH deficiency induces an inflammatory response and activates the p53 pathway. Consequently, loss of seph renders larvae susceptible to oxidative stress and DNA damage. Finally, we demonstrate that seph interacts with p53 deficiency in adulthood to accelerate gastrointestinal tumor development. Overall, our findings establish that seph regulates redox homeostasis and suppresses DNA damage. We hypothesize that SepH deficiency may contribute to the increased cancer risk observed in cohorts with low selenium levels.

Iterative use of nuclear receptor Nr5a2 regulates multiple stages of liver and pancreas development.

The stepwise progression of common endoderm progenitors into differentiated liver and pancreas organs is regulated by a dynamic array of signals that are not well understood. The nuclear receptor subfamily 5, group A, member 2 gene nr5a2, also known as Liver receptor homolog-1 (Lrh-1) is expressed in several tissues including the developing liver and pancreas. Here, we interrogate the role of Nr5a2 at multiple developmental stages using genetic and chemical approaches and uncover novel pleiotropic requirements during zebrafish liver and pancreas development. Zygotic loss of nr5a2 in a targeted genetic null mutant disrupted the development of the exocrine pancreas and liver, while leaving the endocrine pancreas intact. Loss of nr5a2 abrogated exocrine pancreas markers such as trypsin, while pancreas progenitors marked by ptf1a or pdx1 remained unaffected, suggesting a role for Nr5a2 in regulating pancreatic acinar cell differentiation. In the developing liver, Nr5a2 regulates hepatic progenitor outgrowth and differentiation, as nr5a2 mutants exhibited reduced hepatoblast markers hnf4α and prox1 as well as differentiated hepatocyte marker fabp10a. Through the first in vivo use of Nr5a2 chemical antagonist Cpd3, the iterative requirement for Nr5a2 for exocrine pancreas and liver differentiation was temporally elucidated: chemical inhibition of Nr5a2 function during hepatopancreas progenitor specification was sufficient to disrupt exocrine pancreas formation and enhance the size of the embryonic liver, suggesting that Nr5a2 regulates hepatic vs. pancreatic progenitor fate choice. Chemical inhibition of Nr5a2 at a later time during pancreas and liver differentiation was sufficient to block the formation of mature acinar cells and hepatocytes. These findings define critical iterative and pleiotropic roles for Nr5a2 at distinct stages of pancreas and liver organogenesis, and provide novel perspectives for interpreting the role of Nr5a2 in disease.

Cannabinoid Receptor-2 Regulates Embryonic Hematopoietic Stem Cell Development via Prostaglandin E2 and P-Selectin Activity

Cannabinoids (CB) modulate adult hematopoietic stem and progenitor cell (HSPCs) function, however, impact on the production, expansion, or migration of embryonic HSCs is currently uncharacterized. Here, using chemical and genetic approaches targeting CB‐signaling in zebrafish, we show that CB receptor (CNR) 2, but not CNR1, regulates embryonic HSC development. During HSC specification in the aorta‐gonad‐mesonephros (AGM) region, CNR2 stimulation by AM1241 increased runx1;cmyb+ HSPCs, through heightened proliferation, whereas CNR2 antagonism decreased HSPC number; FACS analysis and absolute HSC counts confirmed and quantified these effects. Epistatic investigations showed AM1241 significantly upregulated PGE2 synthesis in a Ptgs2‐dependent manner to increase AGM HSCs. During the phases of HSC production and colonization of secondary niches, AM1241 accelerated migration to the caudal hematopoietic tissue (CHT), the site of embryonic HSC expansion, and the thymus; however these effects occurred independently of PGE2. Using a candidate approach for HSC migration and retention factors, P‐selectin was identified as the functional target of CNR2 regulation. Epistatic analyses confirmed migration of HSCs into the CHT and thymus was dependent on CNR2‐regulated P‐selectin activity. Together, these data suggest CNR2‐signaling optimizes the production, expansion, and migration of embryonic HSCs by modulating multiple downstream signaling pathways. Stem Cells 2015;33:2596—2612

Abstract 1953: The role of NR5a2 in pancreas development and carcinogenesis

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal cancers today. A recent genome-wide association study (GWAS) has implicated the nuclear receptor NR5A2 in modulating risk for pancreatic cancer. While a role for this gene in pancreatic cancer has not been previously recognized, it is known to have an important role in stem cell pluripotency and metabolism. Using the zebrafish model organism, we demonstrate that knockdown of nr5a2 results in absence of exocrine pancreas, while leaving endocrine pancreas unaffected, indicating an essential role in pancreas organ formation. Further, we localize expression of nr5a2 to the endodermal bud that gives rise to the exocrine pancreas, consistent with a role for nr5a2 in regulating differentiation of pancreas progenitors. In resected human PDAC specimens and in vitro cell lines, we find that NR5A2 expression is altered compared to normal ductal epithelium. Moreover, shRNA knockdown of NR5A2 dramatically alters proliferation of PDAC cell lines, supporting the hypothesis that NR5A2 is involved in pancreatic carcinogenesis. These data support a model that NR5a2 regulates the proliferation and differentiation of exocrine pancreas progenitor cells during development. Consistent with this model, we find that signaling through nr5a2 interacts with notch activity. We postulate that aberrant expression of NR5a2 results in dysregulation of these processes in the adult pancreas by driving ductal epithelial cells to acquire properties of progenitor cells, and therefore is an important step in pancreas oncogenesis. Note: This abstract was not presented at the meeting. Citation Format: Sahar Nissim, Julia Wucherpfennig, Xiao-Xu Wang, Alec Kimmelman, Wolfram Goessling. The role of NR5a2 in pancreas development and carcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1953. doi:10.1158/1538-7445.AM2014-1953