Chaperone activity of protein O-fucosyltransferase 1 promotes notch receptor folding

Notch proteins are receptors for a conserved signaling pathway that affects numerous cell fate decisions. We found that in Drosophila, Protein O-fucosyltransferase 1 (OFUT1), an enzyme that glycosylates epidermal growth factor-like domains of Notch, also has a distinct Notch chaperone activity. OFUT1 is an endoplasmic reticulum protein, and its localization was essential for function in vivo. OFUT1 could bind to Notch, was required for the trafficking of wild-type Notch out of the endoplasmic reticulum, and could partially rescue defects in secretion and ligand binding associated with Notch point mutations. This ability of OFUT1 to facilitate folding of Notch did not require its fucosyltransferase activity. Thus, a glycosyltransferase can bind its substrate in the endoplasmic reticulum to facilitate normal folding.     

Notch-mediated restoration of regenerative potential to aged muscle

A hallmark of aging is diminished regenerative potential of tissues, but the mechanism of this decline is unknown. Analysis of injured muscle revealed that, with age, resident precursor cells (satellite cells) had a markedly impaired propensity to proliferate and to produce myoblasts necessary for muscle regeneration. This was due to insufficient up-regulation of the Notch ligand Delta and, thus, diminished activation of Notch in aged, regenerating muscle. Inhibition of Notch impaired regeneration of young muscle, whereas forced activation of Notch restored regenerative potential to old muscle. Thus, Notch signaling is a key determinant of muscle regenerative potential that declines with age.     

Multipotent Drosophila intestinal stem cells specify daughter cell fates by differential notch signaling

The adult Drosophila midgut contains multipotent intestinal stem cells (ISCs) scattered along its basement membrane that have been shown by lineage analysis to generate both enterocytes and enteroendocrine cells. ISCs containing high levels of cytoplasmic Delta-rich vesicles activate the canonical Notch pathway and down-regulate Delta within their daughters, a process that programs these daughters to become enterocytes. ISCs that express little vesiculate Delta, or are genetically impaired in Notch signaling, specify their daughters to become enteroendocrine cells. Thus, ISCs control daughter cell fate by modulating Notch signaling over time. Our studies suggest that ISCs actively coordinate cell production with local tissue requirements by this mechanism.     

Notch signaling: cell fate control and signal integration in development

Notch signaling defines an evolutionarily ancient cell interaction mechanism, which plays a fundamental role in metazoan development. Signals exchanged between neighboring cells through the Notch receptor can amplify and consolidate molecular differences, which eventually dictate cell fates. Thus, Notch signals control how cells respond to intrinsic or extrinsic developmental cues that are necessary to unfold specific developmental programs. Notch activity affects the implementation of differentiation, proliferation, and apoptotic programs, providing a general developmental tool to influence organ formation and morphogenesis.     

Xotch, the Xenopus homolog of Drosophila notch

During the development of a vertebrate embryo, cell fate is determined by inductive signals passing between neighboring tissues. Such determinative interactions have been difficult to characterize fully without knowledge of the molecular mechanisms involved. Mutations of Drosophila and the nematode Caenorhabditis elegans have been isolated that define a family of related gene products involved in similar types of cellular inductions. One of these genes, the Notch gene from Drosophila, is involved with cell fate choices in the neurogenic region of the blastoderm, in the developing nervous system, and in the eye-antennal imaginal disc. Complementary DNA clones were isolated from Xenopus embryos with Notch DNA in order to investigate whether cell-cell interactions in vertebrate embryos also depend on Notch-like molecules. This approach identified a Xenopus molecule, Xotch, which is remarkably similar to Drosophila Notch in both structure and developmental expression.     

乳腺干细胞自我更新相关信号通路研究进展

乳腺干细胞是来源于乳腺组织的一种成体干细胞,具有自我更新和定向分化潜能。乳腺干细胞对乳腺的发育和功能维持具有重要作用。近年来发现,乳腺干细胞与乳腺癌的发生也有密切联系。多条信号通路对乳腺干细胞的自我更新与分化起着重要作用,这些通路包括Wnt、Notch和Hedgehog通路等。了解这些信号通路的调控机制对乳腺干细胞、乳腺发育以及乳腺癌的研究均有重要意义。本文就近年来该方面的进展做一综述,以期为本领域相关研究提供参考。     

Notch信号通路与胰腺发育

Notch信号转导通路作为一种进化上保守的相邻细胞间的相互作用机制,参与了细胞的命运决定、自我更新、分化、增值、存活以及凋亡等诸多过程,调控着动物组织和器官的发生、发育和再生。目前,多因子多信号对胰腺发育的时空调节机制已成为研究热点。就Notch信号通路的结构特点及其在胰腺发育中的研究进展作一综述。     

Interaction between Notch and Hif-alpha in development and survival of Drosophila blood cells

A blood cell type termed crystal cell in Drosophila functions in clotting and wound healing and requires Notch for specification and maintenance. We report that crystal cells express elevated levels of Sima protein orthologous to mammalian hypoxia-inducible factor-α (Hif-α) even under conditions of normal oxygen availability. In these platelet-like crystal cells, Sima activates full-length Notch receptor signaling via a noncanonical, ligand-independent mechanism that promotes hemocyte survival during both normal hematopoietic development and hypoxic stress. This interaction initiates in early endosomes, is independent of Hif-β (Τangο in Drosophila), and does not activate hypoxia response targets. Studies in vertebrate myeloid cells have shown a similar up-regulation of Hif-α protein in well-oxygenated environments. This study provides a mechanistic paradigm for Hif-α/Notch interaction that may be conserved in mammals.     

Instructive role of Wnt/beta-catenin in sensory fate specification in neural crest stem cells

Wnt signaling has recently emerged as a key factor in controlling stem cell expansion. In contrast, we show here that Wnt/beta-catenin signal activation in emigrating neural crest stem cells (NCSCs) has little effect on the population size and instead regulates fate decisions. Sustained beta-catenin activity in neural crest cells promotes the formation of sensory neural cells in vivo at the expense of virtually all other neural crest derivatives. Moreover, Wnt1 is able to instruct early NCSCs (eNCSCs) to adopt a sensory neuronal fate in a beta-catenin-dependent manner. Thus, the role of Wnt/beta-catenin in stem cells is cell-type dependent.     

家蚕Notch信号通路基因的表达研究

[目的]研究家蚕Notch信号通路基因的表达情况。[方法]在实验室前期工作的基础上,用特异引物对家蚕的Notch信号通路上下游基因进行克隆,并对这些基因在家蚕5龄幼虫不同组织部位的表达进行研究。[结果]这些基因在各组织的表达量不同,其中fringe和groucho在家蚕头部表达量较多,在丝腺、精巢、卵巢中的表达量较少;notch在家蚕尾部表达量较少,在其他组织中表达量无明显差别。[结论]该研究为进一步研究家蚕Notch信号通路奠定了基础。     

siRNA干扰Notch1诱导肝癌细胞凋亡的机制研究

目的 研究Notch1在肝癌组织及细胞中的表达并初步探讨Notch1下调后诱导肝癌细胞调亡的机制。方法 2016年3月至2016年9月于广东医科大学附属医院肝胆外科收集32例肝癌病人样本,利用qRT-PCR方法检测肝癌癌组织及癌旁组织中Notch1基因的表达,免疫组化检测组织中Notch1蛋白表达,siRNA沉默肝癌细胞Notch1表达,流式细胞术检测细胞凋亡情况,Western blot方法检测Notch1、Bcl2和Bax蛋白表达,统计分析Notch1表达水平与肝癌病人临床诊断指标甲胎蛋白（AFP）的相关性。结果 肝癌组织标本中Notch1高表达率为71.9%（23/32）,明显高于癌旁组织的28.1%（9/32）,差异具有显著统计学意义（P<0.01）;Pearson相关性分析显示,Notch1与AFP存在正相关性（R²=0.3376,P=0.0036）;免疫组化验证Notch1蛋白分别在肝癌癌组织样本中高表达和癌旁组织中低表达;siRNA干扰Notch1基因表达后,镜下发现肝癌细胞4401增殖抑制,流式检测示转染组明显凋亡,蛋白免疫印迹显示凋亡相关蛋白Bcl2蛋白下调、Bax表达上调。结论 Notch1与肝癌的发生、发展相关,下调Notch1可诱导肝癌细胞凋亡,同时Notch1还可作为临床治疗肝癌的潜在新靶点。     

Cysteine redox sensor in PKGIa enables oxidant-induced activation

Changes in the concentration of oxidants in cells can regulate biochemical signaling mechanisms that control cell function. We have found that guanosine 3',5'-monophosphate (cGMP)-dependent protein kinase (PKG) functions directly as a redox sensor. The Ialpha isoform, PKGIalpha, formed an interprotein disulfide linking its two subunits in cells exposed to exogenous hydrogen peroxide. This oxidation directly activated the kinase in vitro, and in rat cells and tissues. The affinity of the kinase for substrates it phosphorylates was enhanced by disulfide formation. This oxidation-induced activation represents an alternate mechanism for regulation along with the classical activation involving nitric oxide and cGMP. This mechanism underlies cGMP-independent vasorelaxation in response to oxidants in the cardiovascular system and provides a molecular explantion for how hydrogen peroxide can operate as an endothelium-derived hyperpolarizing factor.