tes in the hemosome. doi:10.1371/journal.pone.0134779.g008 previously postulates the existence of one transporter at the hemosome membrane, and data obtained here are compatible with the presence of RmABCB10 
also in the hemosome membrane, as the cytochemical location of the enzyme showed the presence of ATPase activity in the hemosome. However, we cannot exclude the possibility that other ABC transporters, distinct from RmABCB10 or even transporters belonging to other protein family–are also involved in the transport of heme along the digest cell pathway. Moreover, the effect of CsA and RmABCB10 silencing on metalloporphyrin traffic are not identical, as CsA blocks also accumulation in the digestive vesicle. This result suggest that another ABC transporter is needed to allow heme accumulation into the digestive vesicle. These findings point to a scenario that resembles what has been shown for heme transport in the gut of C.elegans, where heme is transferred into a vesicle in the endosome-lysosomal pathway, with one transporter needed to take heme to this compartment and another to direct it to the cytosol. However, in spite of the overall similarity in the general features of the pathway, a major difference needs attention that is the fact that the transporters involved in each organism belong to distinct protein families. This might be attributed to the exceptionally high amount of heme produced by a blood meal, which possibly demanded a dedicated group of proteins as well as the unique digestive system of ticks that is based on intracellular digestion of food instead of the most common use of an extracellular pool of hydrolases in the gut luminal cavity. Also is worth to be mentioned that ticks are probably the oldest hematophagous animals, possibly originated in the middle Permian , but that, accordingly to some authors, may date as early as the Devonian, a time interval that would be enough to allow the development of such a complex heme traffic pathway. In the last few years, a set of proteins conserved among metazoans have been implicated in heme intracellular traffic, specially by the work of Hamza’s group. The hypothesis proposed here that ticks have acquired a specialized heme transport machinery brings about another question that is what is the role of those “pan-metazoa” heme transport proteins in ticks. As already mentioned, the pathway that goes to a hemoglobin-degrading digestive vesicle to the hemosome is dedicated to heme detoxification in this obligate blood-feeding arthropod. The cattle tick has been shown to lack heme biosynthesis, which ONO4059 excludes any connection of the heme cellular trafficking route studied here to this metabolic pathway. Here, we show that heme transportation to the cytosol of tick digest cells is performed by an ABC enzyme. These results also indicate that this is an ancestral mechanism capable of mediating heme transport across PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19756382 membranes, similar to its role in bacteria and trypanosomatids and recently extended to other eukaryotic cells. However, it worth mentioning that the ABC transporter described here belongs to an ABC subfamily distinct from the ABCC5/MRP5 identified in other metazoa, reinforcing the hypothesis that a complete heme transport system has evolved in ticks. ABC transporters have been primarily related to the export of toxic molecules but have also been shown to PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19755711 play a role in the import of nutrients and the transport of many other physiological substrates. As a consequence, a rel