Fig. 4.

ABCB- and ABCC-type transport activity is downregulated in the small micromeres. (A) Average (±s.e.m.) intracellular calcein concentration for the rest of the sea urchin embryo (dashed line) and small micromeres (solid line) after treatment with MK571, an inhibitor of MRP-efflux transporters [n=5×3 (batches × embryos) measured for each concentration] and (B) PSC833, an inhibitor of MDR-efflux transporters (n=4×5). (C) MIP of the vegetal view of a 28-cell and 60-cell embryo treated with the fluorescent ABCG2 substrate 1 μM mitoxantrone. Small micromeres are marked by a white arrow. All of the cells in the embryo accumulate the same amount of mitoxantrone. See also supplementary material Fig. S2. Scale bars: 10 μm.