title: Insight into the ultrastructural organisation of sporulated oocysts of Eimeria nieschulzi (Coccidia, Apicomplexa).
abstract: Sporulated oocysts of Eimeria contain four sporocysts with two sporozoites each and a sporocyst residuum. The developing sporozoites are protected by the sporocyst wall and the robust double-layered oocyst wall. Because of problems with conventional fixatives, high-pressure freezing, followed by freeze substitution was used to achieve optimal ultrastructural preservation of oocysts, sporocysts and sporozoites. After embedding in Epon®, ultrathin sections were examined by electron microscopy to select specific oocyst regions for further investigation by electron tomography (ET). ET allows high-resolution three-dimensional views of subcellular structures within the oocysts and sporocysts. Analysis of several 300 nm sections by ET revealed a network of small tubular structures with a diameter of 70-120 nm inside the sporocysts which is decribed here for the first time. This network connects the residual body in a sporocyst with the endoplasmic reticulum (ER) of the surrounding sporozoites. The network consists of membrane-bound tubules that contain vesicles but no larger organelles like mitochondria. These tubules, named "sporocord", may have a function similar to an "umbilical cord" providing the sporozoites with metabolites for long-term survival. Small vesicular structures inside the ER of the sporozoites, multivesicular structures inside the residual bodies and vesicles in the tubules support this hypothesis.
authors.affiliation: Institute of Zoology, TU Dresden, Zellescher Weg 20B, 01217 Dresden, Germany.
authors.forename: Eric
authors.initials: E
authors.lastname: Seemann
authors.forename: Thomas
authors.initials: T
authors.lastname: Kurth
authors.forename: Rolf
authors.initials: R
authors.lastname: Entzeroth
mesh_terms: D004539:Eimeria / Q000648:ultrastructure*; D055032:Electron Microscope Tomography; D033661:Oocysts / Q000648:ultrastructure*