f a blood meal. Hemosome formation is accomplished by a pathway that starts with specific endocytosis of hemoglobin, followed by the removal of heme from the hemoglobin polypeptide chain inside an acidic digestive vacuole, the subsequent transfer of heme to the cytosol, and finally, the uptake of heme by hemosomes. Heme can account for up to 90% of the dry weight composition of hemosomes. Here, we show evidence that an ABC transporter, the RmABCB10, is involved in heme transport in the digestive vesicles membranes, and is part of a trafficking pathway that leads to heme sequestration into hemosomes, which major features are summarized in a schematic model in Fig 8. The presence of an ABC transporter in the digestive vesicle was demonstrated by immunoreactivity with specific antibody against PgPtype ABC ATPase, together with the identification of ATPase enzymatic activity by cytochemistry and the accumulation of Rhodamine 123, both of which were inhibited by CsA. 12 / 20 ABC-Mediated Heme and Pesticide Detoxification Fig 7. ABC transporter silencing impairs Zn-Pp IX traffic in digest cells. Partially engorged females were collected from cattle and were artificially fed with blood supplemented with dsABC, with Zn-Pp IX plus dsCont or with Zn-Pp IX plus dsABC. In all cases, the blood meal contained 0.5% DMSO. After 72 h ABM, digest cells were detached from the tissue, and PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19756781 differential interference contrast and Zn-Pp IX fluorescence images were acquired. Merged images are shown in B, E and H. The white arrows indicate hemosomes exhibiting a Zn-Pp IX signal in panels A_F; in panels G-I, some hemosomes are indicated, but with no fluorescence associated; white asterisks show digestive vesicles within the Zn-Pp IX signal. The scale bars 
are 20 m in all images. The ratio of the number of Zn-PP positive hemosomes to digestive vesicles was measured in 15 randomly chosen images from each condition, obtained from three MedChemExpress K 858 independent experiments. Data shown are mean SEM; means p value < 0.002. doi:10.1371/journal.pone.0134779.g007 Direct demonstration of ABC-dependent SnPp-IX transport by fluorescence microscopy and HPLC analysis provides evidence that this mechanism is involved in the accumulation of heme. There are a number of reports relating ABC transporters to heme metabolism, showing that cells lacking BCRP/ABCG2 or ABCB6 accumulate porphyrin. ABCB6 is located on the mitochondrial outer membrane, whereas the BCRP protein is localized to inner mitochondrial cristae; both are thought to participate in the uptake of heme precursors into the mitochondria, fueling the final steps of the heme biosynthesis pathway. As already mentioned above, a role of ABCG2 in heme transport has also been hypothesized. In the present work, we observed inhibition of transport of metalloporphyrin to the hemosomes after RmABCB10 dsRNA silencing, together with accumulation in the digestive vesicles, a result that strongly suggests that this enzyme is located in the membrane of the digestive vesicles. In addition to this transporter, the heme traffic pathway in the digestive outlined 13 / 20 ABC-Mediated Heme and Pesticide Detoxification Fig 8. Heme traffic pathway in the digest cell of the cattle tick Rhipicephalus microplus. This proposed model integrates data reported here on the role of ABC transporters and results from previous reports describing the PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19755711 uptake of hemoglobin, followed by export of heme from the digestive vesicle to the cytosol and formation of heme aggrega