Anti-HA antibodies specifically recognize the HA-PfROM1 protein in transgenic HA-PfROM1 3D7 parasites. (B) IFA analysis of HA-PfROM1 in a developing schizont (4 nuclei stage). (C) Merozoites in a segmenter probed with anti-HA rat mAb 3F10 (green) and the nuclear stain (blue, Upper) or with anti-AMA1 (red, Lower). Note in the individual merozoites anti-HA mAb staining appears to be localized on one side of the nucleus, with characteristic bulbous region (arrowheads) that is toward the apical end of the merozoites. The stalk region runs along one side of the nucleus. PfROM1 was not found associated with micronemes, rhoptries, or dense granules, the three identified secretory organelles of invasion. Release of merozoites from schizonts resulted in the movement of PfROM1 from the lateral asymmetric localization to the merozoite apical pole and the posterior pole. We have named this single thread-like organelle in merozoites, the mononeme.Singh S, Plassmeyer M, Gaur D, Miller LH. Mononeme: a new secretory organelle in Plasmodium falciparum merozoites identified by localization of rhomboid-1 protease. Proc Natl Acad Sci U S A. 2007 104:20043-8

Upper panel: Asymmetric organization of organelles confers a lateral polarity in P. falciparum merozoites. Staining with antibodies against different subcellular organelle markers is shown in the left-hand column. (A) a-Tubulin antibodies staining the merozoite subpellicular microtubules. (B) Bip, an ER marker. (C) ERD2, a cis-Golgi marker. (D) ACP, an apicoplast marker. (E) Cytochrome c, a mitochondrial marker. Corresponding costaining with rat anti-HA mAb 3F10 (A and C–E) or mouse anti-HA mAb 2C16 (B) together with nuclear staining with DAPI (blue) and an overlay of all channels is shown in subsequent columns. The right-hand column shows a digital zoom of merozoites showing that the red and green staining occurs on the same side of the nucleus. (Scale bar, 1 mm.) HA-PfROM1 was observed to be localized in close proximity to longitudinal subpellicular microtubules of the merozoite.Lower panel: HA-PfROM1 is secreted on the merozoite surface and concentrates at the posterior pole of the merozoite. Staining of free merozoites with antibodies against a micronemal marker (A) or with a rhoptry marker at the apical end (B) is shown in the left-hand column (red). Corresponding costaining with rat anti-HA mAb 3F10 (green) together with the overlay between the red and green channels is shown in subsequent columns. The right-hand column shows the corresponding DIC image. Arrow heads point to the merozoite posterior pole. (Scale bar, 1 mm.)Singh S, Plassmeyer M, Gaur D, Miller LH. Mononeme: a new secretory organelle in Plasmodium falciparum merozoites identified by localization of rhomboid-1 protease. Proc Natl Acad Sci U S A. 2007 104:20043-8. Copyright 2009 National Academy of Sciences, U.S.A.