Notch信号转导与调控

Notch是一个进化上十分保守的跨膜受体蛋白家族,它可以通过与表达配体的相邻细胞间的相互作用转导信号,从而决定动物系统发育过程中多种细胞的“命运”.Notch信号转导过程包括Notch受体与配体的结合、Notch受体的酶切活化、可溶性NICD转移至细胞核并与CSL DNA结合蛋白相互作用,从而调控靶基因的表达.Notch活性水平、时间和空间分布受到包括配体、蛋白质转运、泛素化降解等多水平内源性和外源性诱导因素的调节.系统介绍了Notch信号转导通路的分子组成、Notch信号激活的生化机制、Notch信号的多水平调节以及与部分相关疾病的关系.     

The abruptex mutations of notch disrupt the establishment of proneural clusters in Drosophila

The receptor encoded by the Notch gene plays a central role in preventing cells from making decisions about their fates until appropriate signals are present. This function of Notch requires the product of the Suppressor of Hairless gene. Loss of either Notch or Suppressor of Hairless function results in cells making premature and incorrect cell fate decisions, whilst increases in Notch signalling prevent cells from making these decisions. Here we find that the proneural clusters are not established correctly in certain Abruptex mutations of Notch and this failure to establish proneural clusters correctly is not due to increased Notch signalling during lateral inhibition. In addition we show that the overexpression of certain dominant negative Notch molecules can disrupt the initiation of proneural cluster development in a manner similar to the Abruptex mutants.     

An activity of Notch regulates JNK signalling and affects dorsal closure in Drosophila.

BACKGROUND: The Drosophila Notch protein is a receptor that controls cell fate during embryonic development, particularly in lateral inhibition, a process that acts on groups of cells that share a particular developmental potential to restrict the number of cells that will adopt that cell fate. The process of lateral inhibition is implemented by the nuclear protein Suppressor of Hairless (Su(H)) and is triggered by the ligand Delta. Recent results have shown that the interaction between Delta and Notch triggers the cleavage of the intracellular domain of Notch which then translocates to the nucleus and binds to Su(H). RESULTS: We find that Notch plays a role in the patterning of the dorsal epidermis of the Drosophila embryo and that this function of Notch is independent of Su(H), requires Notch at the plasma membrane and targets the c-Jun N-terminal kinase (JNK) signalling pathway. Notch mutants show high levels of JNK activity and can rescue the effects of lowered JNK signalling resulting from mutations in the hemipterous and basket genes. Two regions of the intracellular domain of Notch are involved: the Cdc10/ankyrin repeats, which downregulate signalling through the JNK pathway, and a region carboxy-terminal to these repeats, which regulates this negative function. CONCLUSIONS: Our results reveal a novel signalling activity of Notch that does not require its cleavage and acts by modulating signalling through the JNK pathway. In the Drosophila embryo, this activity plays an important role in the morphogenetic movements that drive dorsal closure.     

Notch pathway: making sense of suppressor of hairless

Suppressor of Hairless (Su(H)) is a DNA-binding protein component of the Notch signalling pathway, thought to be required, with a fragment of the Notch receptor, for target gene activation. Recent studies show that this is only one side of the story: target gene enhancers may be regulated by Su(H) in a variety of different ways.     

Wing vein formation in Drosophila melanogaster: hairless is involved in the cross-talk between Notch and EGF signaling pathways

Wing vein development in Drosophila is controlled by different morphogenetic pathways, including Notch. Hairless (H) antagonizes Notch target gene activation by binding to the Notch signal transducer Suppressor of Hairless [Su(H)]. Accordingly, overexpression of H phenocopies reduction of Notch activity. Deletion of the Su(H)-binding domain in H-C2 results in loss of H activity. However, overexpression of H-C2 induces formation of ectopic veins. In a screen for genetic modifiers of this phenotype, we have identified several genes involved in Notch and epidermal growth factor (EGF) signaling. Most notably veinlet, an activator of EGF signaling, acts downstream of H-C2. H-C2 positively regulates veinlet maybe through inhibition of inter-vein determinants in agreement with a model, whereby Notch and EGF signaling pathways cross-regulate vein pre-patterning.     

The activity of Drosophila Hairless is required in pupae but not in embryos to inhibit Notch signal transduction

 Drosophila Hairless (H) encodes a negative regulator of Notch signalling. H activity antagonizes Notch (N) signalling during bristle development at the pupal stage. We show here by clonal analysis that H acts by inhibiting signal transduction rather than by promoting signal production, during both selection of microchaete precursors in the notum and vein cell differentiation in the wing. Allele-specific interactions further suggest that H inhibits Notch signal transduction by interacting directly with Suppressor of Hairless. Unexpectedly, this regulatory function of H appears to be essential only during imaginal development. Using a null allele of H that corresponds to a deletion of the H coding sequence, we show that embryos devoid of both maternal and zygotic gene products develop similarly to wild-type embryos. Thus, H activity is not strictly required to regulate N-mediated cell fate choices in the embryo. Received: 7 October 1997 / Accepted: 24 November 1997