In vertebrates, the animal–vegetal axis is determined during oogenesis and at ovulation, the egg is radially symmetric. In anamniotes, following fertilization, a microtubule-dependent movement leads to the displacement of maternal dorsal determinants from the vegetal pole to the future dorsal side of the embryo, providing the initial breaking of radial symmetry [Weaver C, Kimelman D (2004) Development 131:3491–3499]. These dorsal determinants induce β-catenin nuclear translocation in dorsal cells of the blastula. Previous work in amphibians has shown that secreted Wnt11/5a complexes, regulated by the Wnt antagonist Dkk-1, are required for the initiation of embryonic axis formation [Cha et al. (2009) Curr Biol 29:1573–1580]. In the current study, we determined that the vegetal maternal dorsal determinant in fish is not the Wnt11/5a complex but the canonical Wnt, Wnt8a. Translation of this mRNA and secretion of the Wnt8a protein result in a dorsal-to-ventral gradient of Wnt stimulation, extending across the entire embryo. This gradient is counterbalanced by two Wnt inhibitors, Sfrp1a and Frzb. These proteins are essential to restrict the activation of the canonical Wnt pathway to the dorsal marginal blastomeres by defining the domain where the Wnt8a activity gradient is above the threshold value necessary for triggering the canonical β-catenin pathway. In summary, this study establishes that the zebrafish maternal dorsal determinant, Wnt8a, is required to localize the primary dorsal center, and that the extent of this domain is defined by the activity of two maternally provided Wnt antagonists, Sfrp1a and Frzb.

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Angiomotin (Amot), the founding member of the Motin family, is involved in angiogenesis by regulating endothelial cell motility, and is required for visceral endoderm movement in mice. However, little is known about biological functions of the other two members of the Motin family, Angiomotin-like1 (Amotl1) and Angiomotin-like2 (Amotl2). Here, we have identified zebrafish amotl2 as an Fgf-responsive gene. Zebrafish amotl2 is expressed maternally and in restricted cell types zygotically. Knockdown of amotl2 expression delays epiboly and impairs convergence and extension movement, and amotl2-deficient cells in mosaic embryos fail to migrate properly. This coincides with loss of membrane protrusions and disorder of F-actin. Amotl2 partially co-localizes with RhoB-or EEA1-positive endosomes and the non-receptor tyrosine kinase c-Src. We further demonstrate that Amotl2 interacts preferentially with and facilitates outward translocation of the phosphorylated c-Src, which may in turn regulate the membrane architecture. These data provide the first evidence that amotl2 is essential for cell movements in vertebrate embryos.

The purpose of the present study was to compare the ability of larvae of different species, goldfish (Carassius auratus), zebrafish (Danio rerio), and ayu (Plecoglossus altivelis), to regulate their calcium balance. Whole-body Ca(2+) content and Ca(2+) influx in the larvae of the three species, which were incubated in low- (0.02 mM), mid- (0.2 mM), and high- (2.0 mM) Ca(2+) artificial fresh water from embryonic stages, were compared. The Ca(2+) uptake kinetics were determined in zebrafish and goldfish incubated in high- or low-Ca(2+) artificial fresh water. Ca(2+) content of both zebrafish and ayu acclimated to low-Ca(2+) media were significantly lower than those acclimated to mid- or high-Ca(2+) media. However, Ca(2+) contents of goldfish in low-, mid-, and high-Ca(2+) groups showed no significant differences. In goldfish, Ca(2+) influx in the low-Ca(2+) group was significantly higher than those of the mid- and high-Ca(2+) groups. In contrast, the Ca(2+) influx rate in the low-Ca(2+) group was significantly lower than those in the mid- and high-Ca(2+) groups in zebrafish and ayu. Compared to the high-Ca(2+) group, the low-Ca(2+) group of goldfish showed a 13% increase in the maximal velocity (J(max)) and an 84% decrease in the Michaelis constant (K(m)) for Ca(2+) influx. Smaller changes, i.e., an 8% increase in J(max) and a 67% decrease in K(m), were found in zebrafish larvae. Goldfish possess a more effective Ca(2+) regulatory capacity than do zebrafish and ayu. Differences in the strategies for Ca(2+) balance may be associated with different development patterns and environments in which these fish naturally occur.

Upon stimulation by Wnt ligands, the canonical Wnt/b-catenin signalling pathway results in the stabilization of b-catenin and its translocation into the nucleus to form transcriptionally active complexes with sequence-specific DNA-binding T-cell factor/lymphoid enhancer factor (TCF/LEF) family proteins. In the absence of nuclear b-catenin, TCF proteins act as transcriptional repressors by binding to Groucho/Transducin-Like Enhancer of split (TLE) proteins that function as co-repressors by interacting with histone deacetylases whose activity leads to the generation of transcriptionally silent chromatin. Here we show that the transcription factor Ladybird homeobox 2 (Lbx2) positively controls the Wnt/b-catenin signalling pathway in the posterior lateral and ventral mesoderm of the zebrafish embryo at the gastrula stage, by directly interfering with the binding of Groucho/TLE to TCF, thereby preventing formation of transcription repressor complexes. These findings reveal a novel level of regulation of the canonical Wnt/b-catenin signalling pathway occurring in the nucleus and involving tissue-specific derepression of TCF by Lbx2.

Septins play important roles in regulating development and differentiation. Septin 7 (SEPT7) is a crucial component in orchestrating the septin core complex into highly ordered filamentous structures. Here, we showed that genetic depletion of SEPT7 or treatment with forchlorfenuron (FCF; a compound known to affect septin filament assembly) led to reduced the S phase entry in cell models and zebrafish embryos. In addition to colocalizing with actin filaments, SEPT7 resided in the centrosome, and SEPT7 depletion led to aberrant mitotic spindle pole formation. This mitotic defect was rescued in SEPT7‐deficient cells by wild‐type SEPT7, suggesting that SEPT7 maintained mitotic spindle poles. In addition, we observed disorganized microtubule nucleation and reduced cell migration with SEPT7 depletion. Furthermore, SEPT7 formed a complex with and maintained the abundance of p150glued, the component of centriole subdistal appendages. Depletion of p150glued resulted in a phenotype reminiscent of SEPT7‐deficient cells, and overexpression of p150glued reversed the defective phenotypes. Thus, SEPT7 is a centrosomal protein that maintains proper cell proliferation and microtubule array formation via maintaining the abundance of p150glued.

p150(glued) is the largest subunit of dynactin protein complex, through which cargo vesicles link to the microtubule minus-end directed motor protein dynein. In addition, p150(glued) also locates in the mother centriole where it organizes the subdistal appendage. The components of appendage are dynamically regulated throughout the cell cycle stages, but it is still unclear whether the centrosomal residency of p150(glued) correlated with cell cycle progression. Here we found that p150(glued) was located in the mother centriole during G1/S stage and its centrosomal residency was independent of microtubule transportation. However, the centrosomal p150(glued) became blurred at G2/M phase and this event was not regulated by its phosphorylation. Entering into mitosis, p150(glued) was robustly enriched in the mitotic spindle nearby the spindle poles but not in the centrosome. During serum starvation (G0 stage), p150(glued) appeared at the base of primary cilium and its depletion attenuated starvation-induced primary cilium formation. We also checked its role in the maintenance of centrosome homeostasis and configuration, and found depletion of p150(glued) did not induce centrosome amplification or splitting but inhibited U2OS cell growth. G1 arrest and reduced EdU incorporation were observed in p150(glued) deficient U2OS cells. In addition, cyclin E was downregulated following p150(glued) depletion. The p53/p21 signaling was activated indicating that CDKs were inactivated. The reduced cell growth was ameliorated in the p150(glued) depleted cells when treated with p53 inhibitor. Thus, we have identified the centrosomal targeting of p150(glued) in distinct cell cycle stage and uncovered its role in controlling G1/S transition.

As the worldwide application of nanomaterials in commercial products increases every year, various nanoparticles from industry might present possible risks to aquatic systems and human health. Presently, there are many unknowns about the toxic effects of nanomaterials, especially because the unique physicochemical properties of nanomaterials affect functional and toxic reactions. In our research, we sought to identify the targets and mechanisms for the deleterious effects of two different sizes (~10 and ~50 nm) of amine-modified silver nanoparticles (AgNPs) in a zebrafish embryo model. Fluorescently labeled AgNPs were taken up into embryos via the chorion. The larger-sized AgNPs (LAS) were distributed throughout developing zebrafish tissues to a greater extent than small-sized AgNPs (SAS), which led to an enlarged chorion pore size. Time-course survivorship revealed dose- and particle size-responsive effects, and consequently triggered abnormal phenotypes. LAS exposure led to lysosomal activity changes and higher number of apoptotic cells distributed among the developmental organs of the zebrafish embryo. Overall, AgNPs of ~50 nm in diameter exhibited different behavior from the ~10-nm-diameter AgNPs. The specific toxic effects caused by these differences in nanoscale particle size may result from the different mechanisms, which remain to be further investigated in a follow-up study.