秀丽隐杆线虫固有免疫功能神经调控机制研究进展

固有免疫系统是动植物个体应对外来微生物侵入感染时非常重要的抵御防线。秀丽隐杆线虫(Caenorhabditis elegans,简称线虫)作为研究宿主与病原菌之间相互作用的经典模式动物,近年来在神经和免疫之间相互作用的分子与遗传机制等方面的研究取得了长足进展。研究表明,线虫神经元通过释放神经递质与神经多肽(如多巴胺、NLP-20)等,激活相关信号通路途经,参与线虫对病原菌的识别、逃避、调节物理屏障防御能力和激活固有免疫反应,并表达分泌抗菌肽以清除病原菌等的调控进程。本文综述了线虫神经系统调控固有免疫功能机制的最新研究进展,为人们深入了解神经与免疫系统间相互作用的功能分子及其调控机制和揭示人类神经与免疫系统相关疾病的病理机理提供了重要信息。     

极性蛋白Crumbs胞内域功能保守性研究

跨膜蛋白Crumbs(Crb)是细胞顶部的决定因子,对上皮细胞顶-底极性的建立和维持起着关键的作用。其胞内域虽然仅有37个氨基酸,但对Crb的功能必不可少。在果蝇(Drosophila melanogaster)中,如果胞内域发生突变,将造成胚胎发育异常、上皮细胞顶底极性丧失等严重后果。Crb胞内域从果蝇到小鼠(Mus musculus)和人类(Homo sapiens)具有很高的同源性,但线虫(Caenorhabditis elegans)两个Crb蛋白的胞内域与果蝇和哺乳动物却较为不同。为验证线虫Crb蛋白胞内域是否功能保守,本文利用基因组工程法(Genomic engineering),将果蝇基因组中Crb基因编码胞内域的部分替换为一致性和相似性较远的线虫Crb2基因的相应区段。与其他Crb胞内域突变果蝇不同,替换突变体胚胎发育正常,Crb及其他极性蛋白的表达和定位正常,胚胎上皮细胞顶底极性能够正确的建立和维持。这些结果证实虽然线虫和果蝇Crb蛋白胞内域之间存在大量序列变异,但重要的氨基酸位点和功能模块则完全保守。     

Identification and characterization of a serine hydroxymethyltransferase isoform in Caenorhabditis briggsae

In the nematode Caenorhabditis elegans, the maternal effect lethal gene mel-32 encodes a serine hydroxymethyltransferase isoform. Since interspecies DNA comparison is a valuable tool for identifying sequences that have been conserved because of their functional importance or role in regulating gene activity, mel-32(SHMT) genomic DNA from C. elegans was used to screen a genomic library from the closely related nematode Caenorhabditis briggsae. The C. briggsae genomic clone identified fully rescues the Mel-32 phenotype in C. elegans, indicating functional and regulatory conservation. Computer analysis reveals that CbMEL-32(SHMT) is 92% identical (97% similar) to CeMEL-32(SHMT) at the amino acid level over the entire length of the protein (484 amino acids), whereas the coding DNA is 82.5% identical (over 1455 nucleotides). Several highly conserved non-coding regions upstream and downstream of the mel-32(SHMT) gene reveal potential regulatory sites that may bind trans-acting protein factors.     

The calcium-activated potassium channel, SLO-1, is required for the action of the novel cyclo-octadepsipeptide anthelmintic, emodepside, in Caenorhabditis elegans

The cyclo-octadepsipeptide anthelmintic, emodepside, has pleiotropic effects on the behaviour of the model genetic animal Caenorhabditis elegans: it inhibits locomotion, feeding, egg-laying and slows development. Previous studies on pharyngeal muscle indicated a role for latrophilin-dependent signalling and therefore prompted the suggestion that this is a common effector of this drug’s actions. However, whilst a C. elegans functional null mutant for latrophilin (lat-1) is less sensitive to the effect of emodepside on the pharynx it remains sensitive to the inhibitory effects of emodepside on locomotion. Here we show that this is not due to functional redundancy between two C. elegans latrophilins, as the double mutant, lat-2, lat-1, also remains sensitive to the effects of emodepside on locomotion. Therefore, emodepside has latrophilin-independent effects. To define the molecular basis for this we performed a mutagenesis screen. We recovered nine alleles of slo-1, which encodes a Ca²⁺-activated K⁺ channel. These mutants were highly resistant to the inhibitory effect of emodepside on both pharyngeal and locomotor activity. The slo-1 alleles are predicted to reduce or eliminate SLO-1 signalling, suggesting that emodepside may signal through a SLO-1-dependent pathway. The observation that gain-of-function slo-1 alleles phenocopy the effects of emodepside, but are not themselves emodepside hypersensitive, favours a model whereby emodepside directly acts through a SLO-1-dependent pathway. Tissue-specific genetic rescue experiments reveal that emodepside acts through SLO-1 expressed in either body wall muscle or in neurones to inhibit locomotion. In contrast, in the pharyngeal system, emodepside acts through SLO-1 in neurones, but not muscle, to inhibit feeding. These data further inform understanding of the mode of action of emodepside and suggest that emodepside causes inhibition of feeding via a neuronal SLO-1-dependent pathway which is facilitated by LAT-1 whilst it signals through a latrophilin-independent, SLO-1-dependent pathway, in either neurones or body wall muscle, to inhibit locomotion.