Analyses of zebrafish and Xenopus oocyte maturation reveal conserved and diverged features of translational regulation of maternal cyclin B1 mRNA

<p>Abstract</p> <p>Background</p> <p>Vertebrate development relies on the regulated translation of stored maternal mRNAs, but how these regulatory mechanisms may have evolved to control translational efficiency of individual mRNAs is poorly understood. We compared the translational regulation and polyadenylation of the cyclin B1 mRNA during zebrafish and <it>Xenopus </it>oocyte maturation. Polyadenylation and translational activation of cyclin B1 mRNA is well characterized during <it>Xenopus </it>oocyte maturation. Specifically, <it>Xenopus </it>cyclin B1 mRNA is polyadenylated and translationally activated during oocyte maturation by proteins that recognize the conserved AAUAAA hexanucleotide and U-rich Cytoplasmic Polyadenylation Elements (CPEs) within cyclin B1 mRNA's 3'<b>U</b>n<b>T</b>ranslated <b>R</b>egion (3'<b>UTR</b>).</p> <p>Results</p> <p>The zebrafish cyclin B1 mRNA was polyadenylated during zebrafish oocyte maturation. Furthermore, the zebrafish cyclin B1 mRNA's 3'UTR was sufficient to stimulate translation of a reporter mRNA during zebrafish oocyte maturation. This stimulation required both AAUAAA and U-rich CPE-like sequences. However, in contrast to AAUAAA, the positions and sequences of the functionally defined CPEs were poorly conserved between <it>Xenopus </it>and zebrafish cyclin B1 mRNA 3'UTRs. To determine whether these differences were relevant to translation efficiency, we analyzed the translational activity of reporter mRNAs containing either the zebrafish or <it>Xenopus </it>cyclin B1 mRNA 3'UTRs during both zebrafish and <it>Xenopus </it>oocyte maturation. The zebrafish cyclin B1 3'UTR was quantitatively less effective at stimulating polyadenylation and translation compared to the <it>Xenopus </it>cyclin B1 3'UTR during both zebrafish and <it>Xenopus </it>oocyte maturation.</p> <p>Conclusion</p> <p>Although the factors that regulate translation of maternal mRNAs are highly conserved, the target sequences and overall sequence architecture within the 3'UTR of the cyclin B1 mRNA have diverged to affect translational efficiency, perhaps to optimize levels of cyclin B1 protein required by these different species during their earliest embryonic cell divisions.</p

SLUG transcription factor : a pro-survival and prognostic factor in gastrointestinal stromal tumour

Background: The SLUG transcription factor has been linked with the KIT signalling pathway that is important for gastrointestinal stromal tumour (GIST) tumourigenesis. Its clinical significance in GIST is unknown. Methods: Influence of SLUG expression on cell proliferation and viability were investigated in GIST48 and GIST882 cell lines. The association between tumour SLUG expression in immunohistochemistry and recurrence-free survival (RFS) was studied in two clinical GIST series, one with 187 patients treated with surgery alone, and another one with 313 patients treated with surgery and adjuvant imatinib. Results: SLUG downregulation inhibited cell proliferation, induced cell death in both cell lines, and sensitised GIST882 cells to lower imatinib concentrations. SLUG was expressed in 125 (25.0%) of the 500 clinical GISTs evaluated, and expression was associated with several factors linked with unfavourable prognosis. SLUG expression was associated with unfavourable RFS both when patients were treated with surgery alone (HR = 3.40, 95% CI = 1.67-6.89, P = 0.001) and when treated with surgery plus adjuvant imatinib (HR = 1.83, 95% CI = 1.29-2.60, P = 0.001). Conclusions: GIST patients with high tumour SLUG expression have unfavourable RFS. SLUG may mediate pro-survival signalling in GISTs.Peer reviewe

SNW1 Is a Critical Regulator of Spatial BMP Activity, Neural Plate Border Formation, and Neural Crest Specification in Vertebrate Embryos

In frog and fish embryos, SNW1 is a protein required for the spatio-temporal activity of BMP signaling necessary for neural plate border formation and specification of neural crest tissue

An NF-κB and Slug Regulatory Loop Active in Early Vertebrate Mesoderm

BACKGROUND: In both Drosophila and the mouse, the zinc finger transcription factor Snail is required for mesoderm formation; its vertebrate paralog Slug (Snai2) appears to be required for neural crest formation in the chick and the clawed frog Xenopus laevis. Both Slug and Snail act to induce epithelial to mesenchymal transition (EMT) and to suppress apoptosis. METHODOLOGY & PRINCIPLE FINDINGS: Morpholino-based loss of function studies indicate that Slug is required for the normal expression of both mesodermal and neural crest markers in X. laevis. Both phenotypes are rescued by injection of RNA encoding the anti-apoptotic protein Bcl-xL; Bcl-xL's effects are dependent upon IκB kinase-mediated activation of the bipartite transcription factor NF-κB. NF-κB, in turn, directly up-regulates levels of Slug and Snail RNAs. Slug indirectly up-regulates levels of RNAs encoding the NF-κB subunit proteins RelA, Rel2, and Rel3, and directly down-regulates levels of the pro-apopotic Caspase-9 RNA. CONCLUSIONS/SIGNIFICANCE: These studies reveal a Slug/Snail–NF-κB regulatory circuit, analogous to that present in the early Drosophila embryo, active during mesodermal formation in Xenopus. This is a regulatory interaction of significance both in development and in the course of inflammatory and metastatic disease

DAN (NBL1) promotes collective neural crest migration by restraining uncontrolled invasion

Neural crest cells are both highly migratory and significant to vertebrate organogenesis. However, the signals that regulate neural crest cell migration remain unclear. Here, we test the function of DAN, a BMP antagonist we detected by analysis of chick cranial mesoderm. Our analysis shows that, prior to neural crest cell exit from the hindbrain, DAN is expressed in the mesoderm, then it becomes absent along cell migratory pathways. Cranial neural crest and metastatic melanoma cells avoid DAN protein stripes in vitro. Addition of DAN reduces the speed of migrating cells, in vivo and in vitro respectively. In vivo loss-of-function of DAN results in enhanced neural crest cell migration by increasing speed and directionality. Computer model simulations support the hypothesis that DAN restrains cell migration by regulating cell speed. Taken together, our results identify DAN as a novel factor that inhibits uncontrolled neural crest and metastatic melanoma invasion and promotes collective migration in a manner consistent with inhibition of BMP signaling

Current perspectives of the signaling pathways directing neural crest induction

The neural crest is a migratory population of embryonic cells with a tremendous potential to differentiate and contribute to nearly every organ system in the adult body. Over the past two decades, an incredible amount of research has given us a reasonable understanding of how these cells are generated. Neural crest induction involves the combinatorial input of multiple signaling pathways and transcription factors, and is thought to occur in two phases from gastrulation to neurulation. In the first phase, FGF and Wnt signaling induce NC progenitors at the border of the neural plate, activating the expression of members of the Msx, Pax, and Zic families, among others. In the second phase, BMP, Wnt, and Notch signaling maintain these progenitors and bring about the expression of definitive NC markers including Snail2, FoxD3, and Sox9/10. In recent years, additional signaling molecules and modulators of these pathways have been uncovered, creating an increasingly complex regulatory network. In this work, we provide a comprehensive review of the major signaling pathways that participate in neural crest induction, with a focus on recent developments and current perspectives. We provide a simplified model of early neural crest development and stress similarities and differences between four major model organisms: Xenopus, chick, zebrafish, and mouse