Differential Responses of the Coral Host and Their Algal Symbiont to Thermal Stress

The success of any symbiosis under stress conditions is dependent upon the responses of both partners to that stress. The coral symbiosis is particularly susceptible to small increases of temperature above the long term summer maxima, which leads to the phenomenon known as coral bleaching, where the intracellular dinoflagellate symbionts are expelled. Here we for the first time used quantitative PCR to simultaneously examine the gene expression response of orthologs of the coral Acropora aspera and their dinoflagellate symbiont Symbiodinium. During an experimental bleaching event significant up-regulation of genes involved in stress response (HSP90 and HSP70) and carbon metabolism (glyceraldehyde-3-phosphate dehydrogenase, α-ketoglutarate dehydrogenase, glycogen synthase and glycogen phosphorylase) from the coral host were observed. In contrast in the symbiont, HSP90 expression decreased, while HSP70 levels were increased on only one day, and only the α-ketoglutarate dehydrogenase expression levels were found to increase. In addition the changes seen in expression patterns of the coral host were much larger, up to 10.5 fold, compared to the symbiont response, which in all cases was less than 2-fold. This targeted study of the expression of key metabolic and stress genes demonstrates that the response of the coral and their symbiont vary significantly, also a response in the host transcriptome was observed prior to what has previously been thought to be the temperatures at which thermal stress events occur

Huntingtin Interacting Proteins Are Genetic Modifiers of Neurodegeneration

Huntington's disease (HD) is a fatal neurodegenerative condition caused by expansion of the polyglutamine tract in the huntingtin (Htt) protein. Neuronal toxicity in HD is thought to be, at least in part, a consequence of protein interactions involving mutant Htt. We therefore hypothesized that genetic modifiers of HD neurodegeneration should be enriched among Htt protein interactors. To test this idea, we identified a comprehensive set of Htt interactors using two complementary approaches: high-throughput yeast two-hybrid screening and affinity pull down followed by mass spectrometry. This effort led to the identification of 234 high-confidence Htt-associated proteins, 104 of which were found with the yeast method and 130 with the pull downs. We then tested an arbitrary set of 60 genes encoding interacting proteins for their ability to behave as genetic modifiers of neurodegeneration in a Drosophila model of HD. This high-content validation assay showed that 27 of 60 orthologs tested were high-confidence genetic modifiers, as modification was observed with more than one allele. The 45% hit rate for genetic modifiers seen among the interactors is an order of magnitude higher than the 1%–4% typically observed in unbiased genetic screens. Genetic modifiers were similarly represented among proteins discovered using yeast two-hybrid and pull-down/mass spectrometry methods, supporting the notion that these complementary technologies are equally useful in identifying biologically relevant proteins. Interacting proteins confirmed as modifiers of the neurodegeneration phenotype represent a diverse array of biological functions, including synaptic transmission, cytoskeletal organization, signal transduction, and transcription. Among the modifiers were 17 loss-of-function suppressors of neurodegeneration, which can be considered potential targets for therapeutic intervention. Finally, we show that seven interacting proteins from among 11 tested were able to co-immunoprecipitate with full-length Htt from mouse brain. These studies demonstrate that high-throughput screening for protein interactions combined with genetic validation in a model organism is a powerful approach for identifying novel candidate modifiers of polyglutamine toxicity

Temperature profile and dark-adapted yield for <i>A. aspera</i> during the course of the experiment.

<p>(a) Temperature represents the average of the three experimental tanks (…) and three control tanks (). (b) Dark adapted yield of heated (▪) and control (♦) corals was measured at 18:30 each day after the corals had been dark-adapted for 30 minutes, n = 9, error bars represent standard errors, * represents significant differences between controls and treatments (<i>p</i><0.05).</p

Changes in <i>A. aspera</i> gene expression during a simulated bleaching event.

<p>Changes in gene expression of heated <i>A. aspera</i> nubbins compared to control nubbins on the same day for (a) HSP70, (b) HSP90, (c) GAPDH, (d) α-ketoglutarate dehydrogenase, (e) glycogen synthase, (f) glycogen phosphorylase, (g) glutamine synthetase and (h) malonyl Co-A acyl transferase. Controls (♦) have relative expression values of while heated tanks (▪) are changes in gene expression relative to controls on that day. Error bars represent standard error, n = 6 for each treatment, * represents significant differences between controls and treatments (<i>p</i><0.05).</p

Natural changes in <i>Symbiodinium</i> gene expression.

<p>Changes in gene expression of <i>Symbiodinium</i> from control <i>A. aspera</i> nubbins compared to expression of control nubbins on day one for (a) HSP70, (b) HSP90, (c) GAPDH, (d) α-ketoglutarate dehydrogenase, (e) glutamine synthetase and (f) malonyl Co-A acyl transferase. Error bars represent standard error, n = 6 for each treatment, # represents significant differences from day 1 expression (<i>p</i><0.05).</p

Natural variations in <i>A. aspera</i> gene expression.

<p>Changes in gene expression of control <i>A. aspera</i> nubbins compared to expression of control nubbins on day one for (a) HSP70, (b) HSP90, (c) GAPDH, (d) α-ketoglutarate dehydrogenase, (e) glycogen synthase, (f) glycogen phosphorylase, (g) glutamine synthetase and (h) malonyl Co-A acyl transferase. Error bars represent standard error, n = 6 for each treatment, # represents significant differences from day 1 expression (<i>p</i><0.05).</p

Primer sequences used for quantitative PCR for both <i>A. aspera</i> and <i>Symbiodinium</i> clade C1.

<p>Primer sequences used for quantitative PCR for both <i>A. aspera</i> and <i>Symbiodinium</i> clade C1.</p