背景:海绵(Porifera门)不断与微生物相互作用。它们通过过滤喂养从水柱中吃草的微生物,并且在体内拥有共生伴侣。在实验设置中,与海水微生物相比,海绵以更低的速率吸收共生体。这表明海绵具有区分微生物的能力,并优先在非共生微生物中放牧,尽管对歧视的潜在机制仍然知之甚少。基因组研究表明,与其他动物组相比,海绵提供了一个扩展的免疫受体库,特别是NLR,SRCR,和GPCRs,少数实验表明,海绵在遇到微生物激发子时调节这些受体的表达。我们假设海绵可能依赖于其不同的poriferan免疫受体库的差异表达,以在过滤喂养时感知不同的微生物聚生体。为了测试这个,我们表征了两种海绵物种的转录组反应,Aplysinaaerophoba和Dysideaavara,与与海水微生物孵育相比,与从A.aerophoba提取的微生物聚生体一起孵育。1小时后取样海绵,3h,和5小时用于RNA-Seq差异基因表达分析。
结果:D.与Aerophoba共生体孵育的avara调节与免疫相关的基因的表达,泛素化,和信号。在一组差异表达的免疫基因中,我们鉴定了核苷酸寡聚化结构域(NOD)样受体(NLR)的不同家族。这些结果代表了第一个实验证据,即不同类型的NLR参与海绵中的微生物识别。相比之下,A.aerophoba对其共生体的转录组反应涉及的基因相对较少,并且缺乏编码免疫受体的基因。
结论:我们的工作表明:(i)海绵在微生物暴露后的转录组反应可能意味着由于它们与微生物的相互作用而对基线基因表达进行“微调”,(ii)不同物种之间海绵对微生物接触的不同反应,可能是由于物种特异性特征或与宿主的性状有关,和(iii)属于不同家族的NLR样基因的免疫受体在对微生物的差异反应中起作用,无论是共生生物还是食物细菌。海绵中这些受体的调节进一步证明了NLR在无脊椎动物宿主-微生物相互作用中的潜在作用。海绵对微生物反应的研究说明了研究不同动物群体如何扩大我们对免疫特异性和共生进化的认识。
BACKGROUND: Sponges (phylum Porifera) constantly interact with microbes. They graze on microbes from the water column by filter-feeding and they harbor symbiotic partners within their bodies. In experimental setups, sponges take up symbionts at lower rates compared with seawater microbes. This suggests that sponges have the capacity to differentiate between microbes and preferentially graze in non-symbiotic microbes, although the underlying mechanisms of discrimination are still poorly understood. Genomic studies showed that, compared to other animal groups, sponges present an extended repertoire of immune receptors, in particular
NLRs, SRCRs, and GPCRs, and a handful of experiments showed that sponges regulate the expression of these receptors upon encounter with microbial elicitors. We hypothesize that sponges may rely on differential expression of their diverse repertoire of poriferan immune receptors to sense different microbial consortia while filter-feeding. To test this, we characterized the transcriptomic response of two sponge species, Aplysina aerophoba and Dysidea avara, upon incubation with microbial consortia extracted from A. aerophoba in comparison with incubation with seawater microbes. The sponges were sampled after 1 h, 3 h, and 5 h for RNA-Seq differential gene expression analysis.
RESULTS: D. avara incubated with A. aerophoba-symbionts regulated the expression of genes related to immunity, ubiquitination, and signaling. Within the set of differentially-expressed immune genes we identified different families of Nucleotide Oligomerization Domain (NOD)-Like Receptors (
NLRs). These results represent the first experimental evidence that different types of
NLRs are involved in microbial discrimination in a sponge. In contrast, the transcriptomic response of A. aerophoba to its own symbionts involved comparatively fewer genes and lacked genes encoding for immune receptors.
CONCLUSIONS: Our work suggests that: (i) the transcriptomic response of sponges upon microbial exposure may imply \"fine-tuning\" of baseline gene expression as a result of their interaction with microbes, (ii) the differential response of sponges to microbial encounters varied between the species, probably due to species-specific characteristics or related to host\'s traits, and (iii) immune receptors belonging to different families of NLR-like genes played a role in the differential response to microbes, whether symbionts or food bacteria. The regulation of these receptors in sponges provides further evidence of the potential role of
NLRs in invertebrate host-microbe interactions. The study of sponge responses to microbes exemplifies how investigating different animal groups broadens our knowledge of the evolution of immune specificity and symbiosis.