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Epel, D, Luckenbach T, Stevenson CN, Macmanus-Spencer LA, Hamdoun A, Smital T.  2008.  Efflux transporters: Newly appreciated roles in protection against pollutants. Environmental Science & Technology. 42:3914-3920.   10.1021/es087187v   AbstractWebsite
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.

Whalen, K, Reitzel AM, Hamdoun A.  2012.  Actin polymerization controls the activation of multidrug efflux at fertilization by translocation and fine-scale positioning of ABCB1 on microvilli. Molecular Biology of the Cell. 23:3663-3672.   10.1091/mbc.E12-06-0438   AbstractWebsite

Fertilization changes the structure and function of the cell surface. In sea urchins, these changes include polymerization of cortical actin and a coincident, switch-like increase in the activity of the multidrug efflux transporter ABCB1a. However, it is not clear how cortical reorganization leads to changes in membrane transport physiology. In this study, we used three-dimensional superresolution fluorescence microscopy to resolve the fine-scale movements of the transporter along polymerizing actin filaments, and we show that efflux activity is established after ABCB1a translocates to the tips of the microvilli. Inhibition of actin polymerization or bundle formation prevents tip localization, resulting in the patching of ABCB1a at the cell surface and decreased efflux activity. In contrast, enhanced actin polymerization promotes tip localization. Finally, interference with Rab11, a regulator of apical recycling, inhibits activation of efflux activity in embryos. Together our results show that actin-mediated, short-range traffic and positioning of transporters at the cell surface regulates multidrug efflux activity and highlight the multifaceted roles of microvilli in the spatial distribution of membrane proteins.