Fig. 1.

Formation of young Plasmodium berghei oocysts in vitro. (A–C) P28 (surface) and DAPI (nuclear) staining of ookinetes (A), tooks (B) and young oocysts (C). (D) PbGFP_CON tooks during late transformation in culture. (E) PbGFP_CON early transforming ookinetes in Anopheles stephensi midguts 27 h post-blood feeding (composite of three images). (F) Image adapted from Sinden et al. (1987) (i–iv) to incorporate ookinete to oocyst transformation (v–vii). Transformation begins with a small hump forming on the outer, convex, edge of the ookinete, often towards the apical end. Transforming ookinetes (tooks) then take on a snail-like appearance (v) and the nucleus is observed to move into the developing oocyst. Remnants of the ookinete tips are clearly visible (distinguishing these forms from zygotes; (vi) just prior to the formation of spherical young oocysts. The entire population of ookinetes transform in 12–36 h, depending on nutrient availability.