Stergiopoulos Konstantinos, Cabrero Pablo, Davies Shireen-Anne, Dow Julian A T
Integrative & Systems Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
Physiol Genomics. 2009 Mar 3;37(1):1-11. doi: 10.1152/physiolgenomics.90360.2008. Epub 2008 Nov 18.
To regulate their internal environments, organisms must adapt to varying ion levels in their diet. Adult Drosophila were exposed to dietary salt stress, and their physiological, survival, and gene expression responses monitored. Insects continued to feed on NaCl-elevated diet, although levels >4% wt/vol ultimately proved fatal. Affymetrix microarray analysis of flies fed on diet containing elevated NaCl showed a phased response: the earliest response was widespread upregulation of immune genes, followed by upregulation of carbohydrate metabolism as the immune response was downregulated, then finally a switch to amino acid catabolism and inhibition of genes associated with the reproductive axis. Significantly, the online transcriptomic resource FlyAtlas reports that most of the modulated genes are predominantly expressed in hindgut or Malpighian (renal) tubule, implicating these excretory tissues as the major responders to salt stress. Three genes were selected for further study: the SLC5 symporter CG2196, the GLUT transporter CG6484, and the transcription factor sugarbabe (previously implicated in starvation and stress responses). Expression profiles predicted by microarray were validated by quantitative PCR (qPCR); expression was mapped to the alimentary canal by in situ hybridization. CG2196::eYFP overexpression constructs were localized to the basolateral membrane of the Malpighian (renal) tubules, and RNAi against CG2196 improved survival on high-salt diet, even when driven specifically to just principal cells of the Malpighian tubule, confirming both this tissue and this transporter as major determinants of survival upon salt stress. Accordingly, CG2196 was renamed salty dog (salt).
为了调节其内部环境，生物体必须适应饮食中不同的离子水平。成年果蝇被置于饮食盐胁迫环境中，并监测其生理、存活和基因表达反应。尽管最终证明重量体积比>4%的NaCl水平是致命的，但昆虫仍继续取食NaCl含量升高的食物。对取食含高NaCl食物的果蝇进行的Affymetrix微阵列分析显示出阶段性反应：最早的反应是免疫基因广泛上调，随后随着免疫反应下调，碳水化合物代谢上调，最后转向氨基酸分解代谢并抑制与生殖轴相关的基因。值得注意的是，在线转录组资源FlyAtlas报告称，大多数被调节的基因主要在果蝇后肠或马氏（肾）管中表达，这表明这些排泄组织是对盐胁迫的主要反应者。选择了三个基因进行进一步研究：SLC5同向转运体CG2196、GLUT转运体CG6484和转录因子sugarbabe（以前与饥饿和应激反应有关）。通过定量PCR（qPCR）验证了微阵列预测的表达谱；通过原位杂交将表达定位到消化道。CG2196::eYFP过表达构建体定位于马氏（肾）管的基底外侧膜，针对CG2196的RNA干扰提高了果蝇在高盐饮食下的存活率，即使仅特异性地驱动到马氏管的主细胞，这证实了该组织和该转运体是盐胁迫下存活的主要决定因素。因此，CG2196被重新命名为salty dog（salt）。
