Meeting Abstract

1.8  Monday, Jan. 4  Diversity and complexity of multidrug resistance phenotypes of marine invertebrate oocytes MCGINN, N.A.**; CHERR, G.N.; University of California, Davis namcginn@ucdavis.edu

While multidrug resistance (MDR) was originally described in cancer cells resistant to multiple chemotherapeutic agents, we now know that MDR is utilized by a wide variety of cell types to remove targeted compounds from cells via ATP-dependent, plasma membrane transporters. This fundamentally protective role of MDR is vital to cells in a diverse range of organisms including bacteria, plants, invertebrates, and mammals. MDR activity has been documented in the early life history stages of broadcast-spawning marine invertebrates where MDR is believed to provide a basic defense against xenobiotics well before other mechanisms of detoxification develop. Using a standard assay, we measured the intracellular accumulation of a fluorescent MDR substrate and found that sea urchin eggs had greater MDR activity than oocytes of the echiuran worm Urechis caupo. However, using scanning laser confocal microscopy, we observed that Urechis oocytes exhibited intracellular sequestration of the fluorescent dye within cytoplasmic vesicles identified as lysosomes. This particular MDR phenotype is well established in drug resistant cancer cell lines, but has not previously been observed in normal animal cells. Rather then relying solely on membrane transporters for the efflux of potentially hazardous substances, as is the case in sea urchin eggs, Urechis oocytes use intravesicular sequestration as a second layer of protection. Further, based on our analysis of sea star oocytes, that are similar in maturational state to Urechis oocytes, but from a cleaner habitat similar to that of sea urchins, we conclude that the complexity of the MDR phenotypes observed in Urechis oocytes is likely the result of exposure to the chemically challenging mud burrow habitat of the adult worms.