Rbm8a deficiency causes hematopoietic defects by modulating Wnt/PCP signaling.

Defects in blood development frequently occur among syndromic congenital anomalies. Thrombocytopenia-Absent Radius (TAR) syndrome is a rare congenital condition with reduced platelets (hypomegakaryocytic thrombocytopenia) and forelimb anomalies, concurrent with more variable heart and kidney defects. TAR syndrome associates with hypomorphic gene function for RBM8A/Y14 that encodes a component of the exon junction complex involved in mRNA splicing, transport, and nonsense-mediated decay. How perturbing a general mRNA-processing factor causes the selective TAR Syndrome phenotypes remains unknown. Here, we connect zebrafish rbm8a perturbation to early hematopoietic defects via attenuated non-canonical Wnt/Planar Cell Polarity (PCP) signaling that controls developmental cell re-arrangements. In hypomorphic rbm8a zebrafish, we observe a significant reduction of cd41-positive thrombocytes. rbm8a-mutant zebrafish embryos accumulate mRNAs with individual retained introns, a hallmark of defective nonsense-mediated decay; affected mRNAs include transcripts for non-canonical Wnt/PCP pathway components. We establish that rbm8a-mutant embryos show convergent extension defects and that reduced rbm8a function interacts with perturbations in non-canonical Wnt/PCP pathway genes wnt5b, wnt11f2, fzd7a, and vangl2. Using live-imaging, we found reduced rbm8a function impairs the architecture of the lateral plate mesoderm (LPM) that forms hematopoietic, cardiovascular, kidney, and forelimb skeleton progenitors as affected in TAR Syndrome. Both mutants for rbm8a and for the PCP gene vangl2 feature impaired expression of early hematopoietic/endothelial genes including runx1 and the megakaryocyte regulator gfi1aa. Together, our data propose aberrant LPM patterning and hematopoietic defects as consequence of attenuated non-canonical Wnt/PCP signaling upon reduced rbm8a function. These results also link TAR Syndrome to a potential LPM origin and a developmental mechanism.

Vangl2 deficient zebrafish exhibit hallmarks of neural tube closure defects.

Neural tube defects (NTDs) are among the most devastating and common congenital anomalies worldwide, and the ability to model these conditions in vivo is essential for identifying causative genetic and environmental factors. Although zebrafish are ideal for rapid candidate testing, their neural tubes develop primarily via a solid neural keel rather that the fold-and-fuse method employed by mammals, raising questions about their suitability as an NTD model. Here, we demonstrate that despite outward differences, zebrafish anterior neurulation closely resembles that of mammals. For the first time, we directly observe fusion of the bilateral neural folds to enclose a lumen in zebrafish embryos. The neural folds fuse by zippering between multiple distinct but contiguous closure sites. Embryos lacking vangl2, a core planar cell polarity and NTD risk gene, exhibit delayed neural fold fusion and abnormal neural groove formation, yielding distinct openings and midline bifurcations in the developing neural tube. These data provide direct evidence for fold-and-fuse neurulation in zebrafish and its disruption upon loss of an NTD risk gene, highlighting conservation of vertebrate neurulation and the utility of zebrafish for modeling NTDs.

A role for autophagy in long-term spatial memory formation in male rodents.

A hallmark of long-term memory formation is the requirement for protein synthesis. Administration of protein synthesis inhibitors impairs long-term memory formation without influencing short-term memory. Rapamycin is a specific inhibitor of target of rapamycin complex 1 (TORC1) that has been shown to block protein synthesis and impair long-term memory. In addition to regulating protein synthesis, TORC1 also phosphorylates Unc-51-like autophagy activating kinase-1 (Ulk-1) to suppress autophagy. As autophagy can be activated by rapamycin (and rapamycin inhibits long-term memory), our aim was to test the hypothesis that autophagy inhibitors would enhance long-term memory. To examine if learning alters autophagosome number, we used male reporter mice carrying the GFP-LC3 transgene. Using these mice, we observed that training in the Morris water maze task increases the number of autophagosomes, a finding contrary to our expectations. For learning and memory studies, male Long Evans rats were used due to their relatively larger size (compared to mice), making it easier to perform intrahippocampal infusions in awake, moving animals. When the autophagy inhibitors 3-methyladenine (3-MA) or Spautin-1 were administered bilaterally into the hippocampii prior to training in the Morris water maze task, the drugs did not alter learning. In contrast, when memory was tested 24 hours later by a probe trial, significant impairments were observed. In addition, intrahippocampal infusion of an autophagy activator peptide (TAT-Beclin-1) improved long-term memory. These results indicate that autophagy is not necessary for learning, but is required for long-term memory formation.

Novel Mode of Defective Neural Tube Closure in the Non-Obese Diabetic (NOD) Mouse Strain.

Failure to close the neural tube results in birth defects, with severity ranging from spina bifida to lethal anencephaly. Few genetic risk factors for neural tube defects are known in humans, highlighting the critical role of environmental risk factors, such as maternal diabetes. Yet, it is not well understood how altered maternal metabolism interferes with embryonic development, and with neurulation in particular. We present evidence from two independent mouse models of diabetic pregnancy that identifies impaired migration of nascent mesodermal cells in the primitive streak as the morphogenetic basis underlying the pathogenesis of neural tube defects. We conclude that perturbed gastrulation not only explains the neurulation defects, but also provides a unifying etiology for the broad spectrum of congenital malformations in diabetic pregnancies.

Maternal diet modulates placenta growth and gene expression in a mouse model of diabetic pregnancy.

Unfavorable maternal diet during pregnancy can predispose the offspring to diseases later in life, such as hypertension, metabolic syndrome, and obesity. However, the molecular basis for this phenomenon of "developmental programming" is poorly understood. We have recently shown that a diet nutritionally optimized for pregnancy can nevertheless be harmful in the context of diabetic pregnancy in the mouse, associated with a high incidence of neural tube defects and intrauterine growth restriction. We hypothesized that placental abnormalities may contribute to impaired fetal growth in these pregnancies, and therefore investigated the role of maternal diet in the placenta. LabDiet 5015 diet was associated with reduced placental growth, commencing at midgestation, when compared to pregnancies in which the diabetic dam was fed LabDiet 5001 maintenance chow. Furthermore, by quantitative RT-PCR we identify 34 genes whose expression in placenta at midgestation is modulated by diet, diabetes, or both, establishing biomarkers for gene-environment interactions in the placenta. These results implicate maternal diet as an important factor in pregnancy complications and suggest that the early phases of placenta development could be a critical time window for developmental origins of adult disease.

Maternal diet modulates the risk for neural tube defects in a mouse model of diabetic pregnancy.

Pregnancies complicated by maternal diabetes have long been known to carry a higher risk for congenital malformations, such as neural tube defects. Using the FVB inbred mouse strain and the Streptozotocin-induced diabetes model, we tested whether the incidence of neural tube defects in diabetic pregnancies can be modulated by maternal diet. In a comparison of two commercial mouse diets, which are considered nutritionally replete, we found that maternal consumption of the unfavorable diet was associated with a more than 3-fold higher rate of neural tube defects. Our results demonstrate that maternal diet can act as a modifier of the risk for abnormal development in high-risk pregnancies, and provide support for the possibility that neural tube defects in human diabetic pregnancies might be preventable by optimized maternal nutrition.

Effects of dietary fibers on weight gain, carbohydrate metabolism, and gastric ghrelin gene expression in mice fed a high-fat diet.

Diets that are high in dietary fiber are reported to have substantial health benefits. We sought to compare the metabolic effects of 3 types of dietary fibers -- sugarcane fiber (SCF), psyllium (PSY), and cellulose (CEL) -- on body weight, carbohydrate metabolism, and stomach ghrelin gene expression in a high-fat diet-fed mouse model. Thirty-six male mice (C57BL/6) were randomly divided into 4 groups that consumed high-fat diet alone (HFD) or high-fat diet containing 10% SCF, PSY, and CEL, respectively. After baseline measurements were assessed for body weight, plasma insulin, glucose, leptin, and glucagon-like peptide 1 (GLP-1), animals were treated for 12 weeks. Parameters were reevaluated at the end of study. Whereas there was no difference at the baseline, body weight gains in the PSY and SCF groups were significantly lower than in the CEL group at the end of study. No difference in body weight was observed between the PSY and SCF animals. Body composition analysis demonstrated that fat mass in the SCF group was considerably lower than in the CEL and HFD groups. In addition, fasting plasma glucose and insulin and areas under the curve of intraperitoneal glucose tolerance test were also significantly lower in the SCF and PSY groups than in the CEL and HFD groups. Moreover, fasting plasma concentrations of leptin were significantly lower and GLP-1 level was 2-fold higher in the SCF and PSY mice than in the HFD and CEL mice. Ghrelin messenger RNA levels of stomach in the SCF group were significantly lower than in the CEL and HFD groups as well. These results suggest differences in response to dietary fiber intake in this animal model because high-fat diets incorporating dietary fibers such as SCF and PSY appeared to attenuate weight gain, enhance insulin sensitivity, and modulate leptin and GLP-1 secretion and gastric ghrelin gene expression.

Expression of dominant negative c-jun inhibits ultraviolet B-induced squamous cell carcinoma number and size in an SKH-1 hairless mouse model.

UVB radiation is a complete carcinogen able to initiate, promote, and progress keratinocyte cells toward carcinogenesis. Exposure to UVB leads to the propagation of a number of signal transduction pathways resulting in increased DNA binding of transcription factors, including activator protein-1 (AP-1), and subsequent gene expression. To test the hypothesis that AP-1 activation plays a role in the promotion of UVB-induced skin tumors, a dominant negative c-jun (TAM67) mutant transgene was expressed in the epidermis of SKH-1 hairless mice and bred with mice expressing an AP-1 luciferase reporter gene. Single UVB exposure experiments showed a significant decrease in AP-1 activity, as measured by luciferase levels, in mice expressing TAM67 72 h postexposure. Transgenic and nontransgenic littermates were placed into a chronic UVB exposure experiment, three exposures per week for 25 weeks. Expression of TAM67 reduced the number of tumors per mouse by 58% and tumor sizes were 79% smaller than the tumors present in the nontransgenic study group. These tumors were histologically identified as squamous cell carcinomas. TAM67 had no effect on UVB-induced hyperplasia because comparable epidermal thickening was observed in both study groups over a 5-day period post-UVB exposure. Immunohistochemical analysis showed a reduction in the number of cyclin D(1)-expressing cells in squamous cell carcinoma samples removed from the TAM67 study group. These data show that TAM67 can inhibit UVB-induced squamous cell carcinoma formation, suggesting that AP-1 is a good candidate target for the development of new chemoprevention strategies to prevent sunlight-induced skin cancers.

A dominant negative c-jun specifically blocks okadaic acid-induced skin tumor promotion.

Okadaic acid (OA) is a prototypical non-phorbol ester skin tumor-promoting agent that works by inhibiting protein phosphatases, leading to an increase in protein phosphorylation. Increased protein phosphorylation can lead to stimulated signaling through various signal transduction pathways. One or more of the pathways affected by OA leads to increased signaling via the activator protein 1 (AP-1) transcription factor. Because AP-1 signaling has been shown to be required for skin tumor promotion by phorbol ester, studies were undertaken to determine whether AP-1 signaling is also required for 7,12-dimethylbenz(a)anthracene (DMBA)-initiated/OA-promoted skin tumorigenesis. Transgenic mice expressing a dominant negative c-jun (TAM-67) controlled by the keratin 14 promoter in ICR mice were used to determine the effects of OA on AP-1 signaling. By crossing the TAM-67 mice with mice expressing an AP-1-responsive luciferase, it was shown that TAM-67 decreases AP-1 activation in response to OA treatment by 95%. After 7,12-dimethylbenz(a)anthracene initiation, the TAM-67 mice and nontransgenic littermates were promoted with twice weekly applications of OA. These experiments showed that TAM-67 expression decreased tumor multiplicity by 90%. Additional experiments with TAM-67 mice showed that the hyperplastic response to OA is not impaired in these mice, nor were there differences in OA-induced transcription of various genes known to be AP-1 responsive under other conditions. This result suggests that only a subset of AP-1-regulated genes is targeted by TAM-67 when it prevents tumor promotion by OA. A determination of the mechanism by which TAM-67 can block tumor promotion without affecting hyperplasia will be important.