Immunogold labeling of maturing schizonts with antibody against PfAMA-1 whole ectodomain. (A) An obliquely sectioned merozoite apex with a cluster of micronemes strongly labelled by Pab 1, surrounding the tips of two unlabelled rhoptries (rh). Scale bar, 100 nm. (B) Two micronemes (black arrows) labelled by Pab 3 and a longitudinally sectioned rhoptry devoid of labeling, including its narrow apical end (white arrow). Scale bar, 100 nm. (C,D) PfAMA-1 labelling by Pab 3 around the peripheries of micronemes. The microneme in (D) was situated near the Golgi cisterna and represents an early stage in this organelle’s migration to the apex. Scale bars, 50 nm.Three polyclonal antibodies raised against the recombinant PfAMA-1 ectodomain sequence recognizing both the 83 kDa and processed 66 kDa molecules label the peripheries of translocating and mature micronemes but do not label rhoptries significantly at any stage of merozoite development within schizonts. This result confirms that PfAMA-1 is a micronemal protein, and indicates that within the microneme it is located near or inserted into this organelle’s boundary membrane.

Adapted with permission from Bannister LH, Hopkins JM, Dluzewski AR, Margos G, Williams IT, Blackman MJ, Kocken CH, Thomas AW, Mitchell GH. Plasmodium falciparum apical membrane antigen 1 (PfAMA-1) is translocated within micronemes along subpellicular microtubules during merozoite development. J Cell Sci. 2003 116:3825-34. Copyright Elsevier