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Roepke, TA, Hamdoun AM, Cherr GN.  2006.  Increase in multidrug transport activity is associated with oocyte maturation in sea stars. Development Growth & Differentiation. 48:559-573.   10.1111/j.1440-169x.2006.00893.x   AbstractWebsite

In this study, we report on the presence of efflux transporter activity before oocyte maturation in sea stars and its upregulation after maturation. This activity is similar to the multidrug resistance (MDR) activity mediated by ATP binding cassette (ABC) efflux transporters. In sea star oocytes the efflux activity, as measured by exclusion of calcein-am, increased two-fold 3 h post-maturation. Experiments using specific and non-specific dyes and inhibitors demonstrated that the increase in transporter activity involves an ABCB protein, P-glycoprotein (P-gp), and an ABCC protein similar to the MDR-associated protein (MRP)-like transporters. Western blots using an antibody directed against mammalian P-gp recognized a 45 kDa protein in sea star oocytes that increased in abundance during maturation. An antibody directed against sea urchin ABCC proteins (MRP) recognized three proteins in immature oocytes and two in mature oocytes. Experiments using inhibitors suggest that translation and microtubule function are both required for post-maturation increases in transporter activity. Immunolabeling revealed translocation of stored ABCB proteins to the plasma cell membrane during maturation, and this translocation coincided with increased transport activity. These MDR transporters serve protective roles in oocytes and eggs, as demonstrated by sensitization of the oocytes to the maturation inhibitor, vinblastine, by MRP and PGP-specific transporter inhibitors.

Hamdoun, AM, Cherr GN, Roepke TA, Epel D.  2004.  Activation of multidrug efflux transporter activity at fertilization in sea urchin embryos (Strongylocentrotus purpuratus). Developmental Biology. 276:452-462.   10.1016/j.ydbio.2004.09.013   AbstractWebsite

This study presents functional and molecular evidence for acquisition of multidrug transporter-mediated efflux activity as a consequence of fertilization in the sea urchin. Sea urchin eggs and embryos express low levels of efflux transporter genes with homology to the multidrug resistance associated protein (mrp) and permeability glycoprotein (p-gp) families of ABC transporters. The corresponding efflux activity is low in unfertilized eggs but is dramatically upregulated within 25 min of fertilization; the expression of this activity does not involve de novo gene expression and is insensitive to inhibitors of transcription and translation indicating activation of pre-existing transporter protein. Our study, using specific inhibitors of efflux transporters, indicates that the major activity is from one or more mrp-like transporters. The expression of activity at fertilization requires microfilaments, suggesting that the transporters are in vesicles and moved to the surface after fertilization. Pharmacological inhibition of mrp-mediated efflux activity with MK571 sensitizes embryos to the toxic compound vinblastine, confirming that one role for the efflux transport activity is embryo protection from xenobiotics. In addition, inhibition of mrp activity with MK571 alone retards mitosis indicating that mrp-like activity may also be required for early cell divisions. (C) 2004 Elsevier Inc. All rights reserved.