Search

Morphogen gradients govern tissue patterning. These gradients provide positional information, instructing cells to adopt distinct fates. Over the past few decades, extensive studies have revealed the detailed mechanisms by which morphogens generate tissue patterns. However, the communication between morphogen-receiving cells is still poorly understood. Here, I describe how cadherin-mediated cell competition ensures robust morphogen-gradient formation. In normal zebrafish embryos, unfit cells with abnormal Wnt signaling activity spontaneously appear and produce a noisy morphogen gradient. These unfit cells communicate with neighboring cells through cadherins and are subsequently killed by cell competition. This process of killing unfit cells corrects noisy gradients to support reproducible patterning. I also discuss the significance of cell-competition-mediated morphogen-gradient correction from the perspectives of evolution and disease biology. [Display omitted] • Wnt morphogen gradients produce gradients of cadherin in embryos. • Even normal embryos generate unfit cells producing noise in the morphogen gradient. • Communication between unfit and neighboring fit cells through cadherin stimulates cell competition-mediated unfit cell death. • Cadherin-mediated cell competition corrects noisy gradients to support robust patterning. [ABSTRACT FROM AUTHOR]

Background: Leukaemia stem cells (LSC) have been associated with disease relapse and chemotherapy resistance. Betulonic acid (BA), a pentacyclic lupane-type triterpenoid, was reported to exhibit cytotoxicity toward various cancer cells and to be capable of inducing intrinsic apoptosis in solid tumours. However, the in vitro and in vivo apoptotic effects of BA against LSC remain unknown.Hypothesis/purpose: We aimed to determine whether BA isolated from bark of Walsura pinnata Hassk (Meliaceae) has pro-apoptotic effects on LSC in in vitro and in vivo models.Study Design/methods: The population of high purity LSC was isolated from the Kasumi-1 cell line using magnetic sorting and characterised by flow cytometry. Cell viability was assessed using the MTS assay to examine dose- and time-dependent effects. The colony formation assay was performed in MethoCult® H4435 enriched media. Apoptosis was analysed using Annexin-V and propidium iodide staining, mitochondrial transmembrane potential was studied using JC-1 staining, and expression of apoptosis related genes (BAX, Bcl-2 and survivin) was evaluated by real time-polymerase chain reaction (RT-PCR). Caspase 3/7 and 9 activities were monitored through Promega Caspase-Glo® over a period of 24h. The in vivo antileukaemia activity was evaluated using LSC xenotransplanted zebrafish, observed for DNA fragmentation from apoptosis by TUNEL assay.Results: BA maintained its potency against the LSC population in comparison to parental Kasumi-1 cells (fold differences ≤ 1.94) over various treatment time points and significantly inhibited the formation of colonies by LSC. Apoptosis was triggered by BA through the upregulation of BAX and suppression of Bcl-2 and survivin genes with the loss of mitochondrial transmembrane potential, leading to the activation of caspase 9 followed by downstream caspase 3/7. BA was able to suppressed leukaemia formation and induced apoptosis in LSC xenotransplanted zebrafish.Conclusions: The results demonstrate that BA inhibited the proliferative and colonogenic properties of LSC. BA induced apoptosis in LSC through the mitochondria pathway and was effective in the in vivo zebrafish model. Therefore, BA could be a lead compound for further development into a chemotherapy agent against LSC. [ABSTRACT FROM AUTHOR]

In vertebrates, newly emerging transformed cells are often apically extruded from epithelial layers through cell competition with surrounding normal epithelial cells. However, the underlying molecular mechanism remains elusive. Here, using phospho-SILAC screening, we show that phosphorylation of AHNAK2 is elevated in normal cells neighboring RasV12 cells soon after the induction of RasV12 expression, which is mediated by calcium-dependent protein kinase C. In addition, transient upsurges of intracellular calcium, which we call calcium sparks, frequently occur in normal cells neighboring RasV12 cells, which are mediated by mechanosensitive calcium channel TRPC1 upon membrane stretching. Calcium sparks then enhance cell movements of both normal and RasV12 cells through phosphorylation of AHNAK2 and promote apical extrusion. Moreover, comparable calcium sparks positively regulate apical extrusion of RasV12-transformed cells in zebrafish larvae as well. Hence, calcium sparks play a crucial role in the elimination of transformed cells at the early phase of cell competition. [Display omitted] • Phosphorylation of AHNAK2 is elevated in normal cells neighboring transformed cells • TRPC1-mediated calcium sparks in normal cells mediate the AHNAK2 phosphorylation • Calcium sparks promote tissue fluidity and apical extrusion of transformed cells • Comparable calcium sparks regulate apical extrusion in cultured cells and zebrafish Kuromiya et al. use mammalian cell culture and zebrafish systems to show that calcium sparks frequently occur in normal epithelial cells neighboring RasV12-transformed cells at the early phase of cell competition. Calcium sparks then promote epithelial tissue fluidity and apical extrusion of transformed cells through the phosphorylation of AHNAK2. [ABSTRACT FROM AUTHOR]

Summary The phosphoprotein Dishevelled (Dvl) is a common essential component of Wnt/β-catenin and Wnt/planar cell polarity (PCP) signaling pathways. However, the regulation and significance of Dvl phosphorylation are not fully understood. Here, we show that homeodomain-interacting protein kinase 2 (Hipk2) facilitates protein phosphatase 1 catalytic subunit (PP1c)-mediated dephosphorylation of Dvl via its C-terminal domain and that this dephosphorylation blocks ubiquitination and consequent degradation mediated by the E3 ubiquitin ligase Itch, which targets the phosphorylated form of Dvl proteins. Inhibition of Hipk2 or PP1c function reduces Dvl protein levels and suppresses Wnt/β-catenin and Wnt/PCP pathway-dependent events in mammalian cells and zebrafish embryos, suggesting that Hipk2 and PP1c are essential for maintaining Dvl protein levels that are sufficient to activate Wnt signaling. We also show that Wnt-3a, a Wnt/β-catenin ligand, induces dissociation of the Dvl-Hipk2-PP1c complex and Dvl degradation under high-cell-density conditions. This regulation may be a negative feedback mechanism that fine-tunes Wnt/β-catenin signaling. [ABSTRACT FROM AUTHOR]

Abstract: Nemo-like kinase (NLK) is an evolutionarily conserved MAP kinase-related kinase. Although NLK was originally identified as a Drosophila gene affecting cell movement during eye development, recent studies show that NLK also contributes to cell proliferation, differentiation, and morphological changes during early embryogenesis and nervous system development in vertebrates. In addition, NLK has been reported to be involved in the development of several human cancers. NLK is able to play a role in multiple processes due to its capacity to regulate a diverse array of signaling pathways, including the Wnt/β-catenin, Activin, IL-6, and Notch signaling pathways. Although the molecular mechanisms that regulate NLK activity remain unclear, our recent research has presented a new model for NLK activation. Here, we summarize the current understanding of the function and regulation of NLK and discuss the aspects of NLK regulation that remain to be resolved. [Copyright &y& Elsevier]

Abstract: In order to compare secondary electron images of insulating materials obtained using scanning ion and scanning electron microscopes, secondary electron (SE) emission from SiO2 under Ga ion and electron bombardment was simulated by a Monte Carlo model. The model is characterized by SE generation by excitation of valence electrons across a large energy gap and the energy loss of low-energy SEs via interaction with phonons. The calculated SE yield under electron bombardment was much larger for SiO2 than for Si, as in many experiments, while showing a decrease with increasing material temperature. Due to a threshold effect originating from a large energy gap, the SE yield under Ga ion bombardment was smaller for SiO2 than for Si at energies of a few tens of keV. The calculated depth distributions of SEs that escaped from the surface showed the electron escape depth is larger for SiO2 than for Si, whereas the lateral distributions are much wider for electron bombardment than for Ga ion bombardment. [Copyright &y& Elsevier]

Establishment of robust gene expression boundary is crucial for creating elaborate morphology during development. However, mechanisms underlying boundary formation have been extensively studied only in a few model systems. We examined the establishment of zic1/zic4 -expression boundary demarcating dorsoventral boundary of the entire trunk of medaka fish (Oryzias latipes) and identified a subgroup of dermomyotomal cells called horizontal boundary cells (HBCs) as crucial players for the boundary formation. Embryological and genetic analyses demonstrated that HBCs play crucial roles in the two major events of the process, i.e., refinement and maintenance. In the refinement, HBCs could serve as a chemical barrier against Wnts from the neural tube by expressing Hhip. At later stages, HBCs participate in the maintenance of the boundary by differentiating into the horizontal myoseptum physically inhibiting cell mixing across the boundary. These findings reveal the mechanisms underlying the dorsoventral boundary in the teleost trunk by specialized boundary cells. • Horizontal boundary cells (HBCs) contribute to the horizontal myoseptum • HBCs are crucial for the formation of dorsoventral compartments in teleost myotome • HBCs express Hhip involved in the refinement of dorsoventral boundary • Hhip in HBCs exerts its effect through sequestering Wnt ligands Abe et al. find horizontal boundary cells (HBCs) crucial players for the formation of the dorsoventral compartments of the teleost myotome. HBCs express Hhip, which is necessary for the refinement of the boundary, and they contribute to the horizontal myoseptum, an anatomical structure dividing the dorsoventral compartments. [ABSTRACT FROM AUTHOR]

Mice null for wild-type p53-induced phosphatase 1 (WIP1) display defects in testis development and spermatogenesis, resulting in reduced fertility. However, the molecular mechanism underlying these abnormalities in the testis remains uncharacterized. We report that the phosphatase activity of WIP1 increases Wnt activity through Nemo-like kinase (NLK). WIP1 directly interacted with NLK, which is highly homologous to p38 MAPK, a WIP1 substrate, and dephosphorylated its activation site. The WIP1-mediated inhibition of NLK activity markedly decreased the phosphorylation of lymphoid enhancer-binding factor 1 (LEF1), enhancing its interaction with β-catenin. Additionally, WIP1 depletion impaired germ cell development, as evidenced by the expression of Oct4 and the germ cell-specific markers Ddx4 , Nanos3 and Dnd1 during the development of germ cells from Oct4-GFP transgenic (OG2) mouse embryonic stem cells (mESCs). The expression of WIP1, whose level was significantly lower after the differentiation of germ cells from mESCs, occurred in parallel with the expression of germ cell development markers and SRY-box 17 ( Sox17 ), a downstream target of Wnt. These results indicate that WIP1 is essential for germ cell development, which is known to require Wnt activity. [ABSTRACT FROM AUTHOR]