Eaf1 and Eaf2 negatively regulate canonical Wnt/ß-catenin signaling.

Eaf factors play a crucial role in tumor suppression and embryogenesis. To investigate the potential mechanism of Eaf activity, we performed loss- and gain-of-function assays in zebrafish using morpholino and mRNA injections, respectively. We found that eaf1 and eaf2 inhibit Wnt/ß-catenin signaling, thereby modulating mesodermal and neural patterning in the embryo. Moreover, ectopic expression of eaf1 and eaf2 in embryos and cultured cells blocked ß-catenin reporter activity. By immunoprecipitation, we also observed that Eaf1 and Eaf2 bound to the Armadillo repeat region and C-terminus of ß-catenin, as well as to other ß-catenin transcription complex proteins, such as c-Jun, Tcf and Axin, suggesting the formation of a novel complex. In addition, the N-terminus of Eaf1 and Eaf2 bound to ß-catenin and exhibited dominant-negative activity, whereas the C-terminus appeared to either harbor a suppression domain or to recruit a repressor. Both the N- and C-terminus must be intact for Eaf1 and Eaf2 suppressive activity. Lastly, we demonstrate a conservation of biological activities for Eaf family proteins across species. In summary, our evidence points to a novel role for Eaf1 and Eaf2 in inhibiting canonical Wnt/ß-catenin signaling, which might form the mechanistic basis for Eaf1 and Eaf2 tumor suppressor activity.

Zebrafish eaf1 suppresses foxo3b expression to modulate transcriptional activity of gata1 and spi1 in primitive hematopoiesis.

Studies implicate a potential role for EAF1 in MLL-ELL induced leukemogenesis; however the biological function of EAF1 in this process remains unknown. In this study, we show that knockdown of zebrafish eaf1 by morpholinos caused serious defects in both primitive and definitive hematopoiesis. Using microarray analysis, we identified foxo3b as a target gene suppressed by eaf1. Ectopic expression of foxo3b in embryos mimicked the phenotypes exhibited in eaf1 morphants, except that foxo3b had no effect on runx1 and c-myb expression while eaf1 morphants did not express these markers in the ventral wall of dorsal aorta. Subsequent experiments showed that a dominant negative form of Foxo3b (dn-foxo3b) partially restored primitive hematopoietic defects in eaf1 morphants, suggesting that foxo3b might serve as a key factor for mediating eaf1 function in primitive hematopoiesis. Furthermore, we observed that foxo3b inhibited the transcriptional activity of gata1 and spi1 through protein-protein interaction. Our findings not only suggest a function of eaf1 on hematopoiesis in vivo, but also reveal a novel regulatory pathway, eaf1-foxo3b-gata1/spi1, that may shed light on the role of EAF1 in MLL-ELL induced leukemogenesis.

TDMPP activation of estrogen receptor 2a regulates smc2 and p53 signaling to interfere with liver development in zebrafish (Danio rerio).

Tris (2,6-dimethylphenyl) phosphate (TDMPP), a novel organic phosphorus flame retardant (OPFR), has been found to have estrogenic activity. Estrogens are critical in regulating various biological responses during liver development. However, the effects of TDMPP on zebrafish liver development remain largely unexplored. Here, we utilized a chemical genetic screening approach to assess the estrogenic effects of TDMPP on liver development and to elucidate the underlying molecular mechanism. Our findings revealed that zebrafish larvae exposed to environmentally relevant concentrations of TDMPP (0.05 and 0.5 µM) exhibited concentration-dependent liver impairments, including reduced liver size, histopathological changes, and hepatocyte apoptosis. In addition, E2 caused similar adverse effects to TDMPP, but the pharmacological blockade of estrogen synthesis alleviated the effects on liver development. Chemical inhibitors and morpholino knockdown assays indicated that the reduction of esr2a blocked TDMPP-induced liver impairments, which was further confirmed in the esr2a-/- mutant line. Subsequently, transcriptomic analysis showed that the estrogen receptor activated by TDMPP inhibited the expression of smc2, which was linked to the suppression of liver development through p53 activation. Consistently, overexpression of smc2 and inhibition of p53 evidently rescued hepatic damages induced by TDMPP. Taken together, the above findings identified esr2a, downstream smc2, and p53 as important regulators for the estrogenic effects of TDMPP on liver development. Our work fills crucial gaps in the current knowledge of TDMPP's hepatotoxicity, providing new insights into the adverse effects of TDMPP and the molecular mechanisms of action. These findings underscore the need for further ecological risk assessment and regulatory considerations.

Highly sensitive response to the toxicity of environmental chemicals in transparent casper zebrafish.

The response sensitivity to toxic substances is the most concerned performance of animal model in chemical risk assessment. Casper (mitfaw2/w2;mpv17a9/a9), a transparent zebrafish mutant, is a useful in vivo model for toxicological assessment. However, the ability of casper to respond to the toxicity of exogenous chemicals is unknown. In this study, zebrafish embryos were exposed to five environmental chemicals, chlorpyrifos, lindane, α-endosulfan, bisphenol A, tetrabromobisphenol A (TBBPA), and an antiepileptic drug valproic acid. The half-lethal concentration (LC50) values of these chemicals in casper embryos were 62-87 % of that in the wild-type. After TBBPA exposure, the occurrence of developmental defects in the posterior blood island of casper embryos was increased by 67-77 % in relative to the wild-type, and the half-maximal effective concentration (EC50) in casper was 73 % of that in the wild-type. Moreover, the casper genetic background significantly increased the hyperlocomotion caused by chlorpyrifos and lindane exposure compared with the wild-type. These results demonstrated that casper had greater susceptibility to toxicity than wild-type zebrafish in acute toxicity, developmental toxicity and neurobehavioral toxicity assessments. Our data will inform future toxicological studies in casper and accelerate the development of efficient approaches and strategies for toxicity assessment via the use of casper.

Interception of host fatty acid metabolism by mycobacteria under hypoxia to suppress anti-TB immunity.

Pathogenic mycobacteria induce the formation of hypoxic granulomas during latent tuberculosis (TB) infection, in which the immune system contains, but fails to eliminate the mycobacteria. Fatty acid metabolism-related genes are relatively overrepresented in the mycobacterial genome and mycobacteria favor host-derived fatty acids as nutrient sources. However, whether and how mycobacteria modulate host fatty acid metabolism to drive granuloma progression remains unknown. Here, we report that mycobacteria under hypoxia markedly secrete the protein Rv0859/MMAR_4677 (Fatty-acid degradation A, FadA), which is also enriched in tuberculous granulomas. FadA acts as an acetyltransferase that converts host acetyl-CoA to acetoacetyl-CoA. The reduced acetyl-CoA level suppresses H3K9Ac-mediated expression of the host proinflammatory cytokine Il6, thus promoting granuloma progression. Moreover, supplementation of acetate increases the level of acetyl-CoA and inhibits the formation of granulomas. Our findings suggest an unexpected mechanism of a hypoxia-induced mycobacterial protein suppressing host immunity via modulation of host fatty acid metabolism and raise the possibility of a novel therapeutic strategy for TB infection.

Eaf1 and Eaf2 mediate zebrafish dorsal-ventral axis patterning via suppressing Wnt/ß-Catenin activity.

During early vertebrate embryogenesis, maternal Wnt/ß-catenin signaling is thought to locally initiate expression of dorsal-specific genes. Here, eaf1 and eaf2 were identified as important maternal and zygotic modulators of Wnt signaling to initiate and specify ventral genes. Expression of ventral ved, vent, and vox was all obviously enhanced in either maternal or zygotic eaf1/2 morphants, and in both eaf1 heterozygous and homozygous mutants, but their expression was suppressed in embryos with over-expression of eaf1/2. Additionally, eaf1/2 were revealed to suppress ventral fates in embryos via Wnt/ß-catenin1/Tcf signaling, complimentary to their roles in suppressing dorsal fates via Wnt/ß-catenin2 signaling. Moreover, eaf1/2 were also revealed to obviously suppress the expression of axin2 induced by ß-catenin2 rather than by ß-catenin1, and the dorsal expression of axin2 in embryos was obviously suppressed by ectopic expression of eaf1/2. This study uncovers a novel dorsal-ventral patterning pathway, with eaf1 and eaf2 inhibiting ventral cells via suppressing Wnt/ß-catenin1/Tcf signaling and inducing dorsal cells indirectly via suppressing ß-catenin2-induced-axin2 on the dorsal side of embryos.

Zebrafish foxo3b negatively regulates canonical Wnt signaling to affect early embryogenesis.

FOXO genes are involved in many aspects of development and vascular homeostasis by regulating cell apoptosis, proliferation, and the control of oxidative stress. In addition, FOXO genes have been showed to inhibit Wnt/ß-catenin signaling by competing with T cell factor to bind to ß-catenin. However, how important of this inhibition in vivo, particularly in embryogenesis is still unknown. To demonstrate the roles of FOXO genes in embryogenesis will help us to further understand their relevant physiological functions. Zebrafish foxo3b gene, an orthologue of mammalian FOXO3, was expressed maternally and distributed ubiquitously during early embryogenesis and later restricted to brain. After morpholino-mediated knockdown of foxo3b, the zebrafish embryos exhibited defects in axis and neuroectoderm formation, suggesting its critical role in early embryogenesis. The embryo-developmental marker gene staining at different stages, phenotype analysis and rescue assays revealed that foxo3b acted its role through negatively regulating both maternal and zygotic Wnt/ß-catenin signaling. Moreover, we found that foxo3b could interact with zebrafish ß-catenin1 and ß-catenin2 to suppress their transactivation in vitro and in vivo, further confirming its role relevant to the inhibition of Wnt/ß-catenin signaling. Taken together, we revealed that foxo3b played a very important role in embryogenesis and negatively regulated maternal and zygotic Wnt/ß-catenin signaling by directly interacting with both ß-catenin1 and ß-catenin2. Our studies provide an in vivo model for illustrating function of FOXO transcription factors in embryogenesis.