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Hamdoun, AM, Cheney DP, Cherr GN.  2003.  Phenotypic plasticity of HSP70 and HSP70 gene expression in the Pacific oyster (Crassostrea gigas): Implications for thermal limits and induction of thermal tolerance. Biological Bulletin. 205:160-169.   10.2307/1543236   AbstractWebsite

Pacific oysters, Crassostrea gigas, living at a range of tidal heights, routinely encounter large seasonal fluctuations in temperature. We demonstrate that the thermal limits of oysters are relatively plastic, and that these limits are correlated with changes in the expression of one family of heat-shock proteins (HSP70). Oysters were cultured in the intertidal zone, at two tidal heights, and monitored for changes in expression of cognate (HSC) and inducible (HSP) heat-shock proteins during the progression from spring through winter. We found that the "control" levels (i.e., prior to laboratory heat shock) of HSC77 and HSC72 are positively correlated with increases in ambient temperature and were significantly higher in August than in January. The elevated level of HSCs during the summer was associated with moderate, 2-3 degreesC, increases in the upper thermal limits for survival. We measured concomitant increases in the threshold temperatures (T-on) required for induction of HSP70. Total hsp70 mRNA expression reflected the seasonal changes in the expression of inducible but not cognate members of the HSP70 family of proteins. A potential cost of increased T-on in the summer is that there was no extension of the upper thermal limits for survival (i.e., induction of thermotolerance) after sublethal heat shock at temperatures that were sufficient to induce thermotolerance during the winter months.

Campanale, JP, Hamdoun A.  2012.  Programmed reduction of ABC transporter activity in sea urchin germline progenitors. Development. 139:783-792.   10.1242/dev.076752   AbstractWebsite

ATP-binding cassette (ABC) transporters protect embryos and stem cells from mutagens and pump morphogens that control cell fate and migration. In this study, we measured dynamics of ABC transporter activity during formation of sea urchin embryonic cells necessary for the production of gametes, termed the small micromeres. Unexpectedly, we found small micromeres accumulate 2.32 times more of the ABC transporter substrates calcein-AM, CellTrace RedOrange, BoDipy-verapamil and BoDipy-vinblastine, than any other cell in the embryo, indicating a reduction in multidrug efflux activity. The reduction in small micromere ABC transporter activity is mediated by a pulse of endocytosis occurring 20-60 minutes after the appearance of the micromeres - the precursors of the small micromeres. Treating embryos with phenylarsine oxide, an inhibitor of endocytosis, prevents the reduction of transporter activity. Tetramethylrhodamine dextran and cholera toxin B uptake experiments indicate that micromeres have higher rates of bulk and raft-associated membrane endocytosis during the window of transporter downregulation. We hypothesized that this loss of efflux transport could be required for the detection of developmental signaling molecules such as germ cell chemoattractants. Consistent with this hypothesis, we found that the inhibition of ABCB and ABCC-types of efflux transporters disrupts the ordered distribution of small micromeres to the left and right coelomic pouches. These results point to tradeoffs between signaling and the protective functions of the transporters.