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First published online 13 March 2007
doi: 10.1242/jcs.03402

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Analogs of the Golgi complex in microsporidia: structure and avesicular mechanisms of function

Galina V. Beznoussenko^1,*, Viacheslav V. Dolgikh^2,*, Elena V. Seliverstova³, Petr B. Semenov², Yuri S. Tokarev², Alvar Trucco¹, Massimo Micaroni¹, Daniele Di Giandomenico¹, Peter Auinger⁴, Igor V. Senderskiy², Sergei O. Skarlato⁵, Ekaterina S. Snigirevskaya⁵, Yan Yu. Komissarchik⁵, Margit Pavelka⁴, Maria A. De Matteis¹, Alberto Luini¹, Yuliya Ya. Sokolova^5, and Alexander A. Mironov^1,,

¹ Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale, 66030 Santa Maria Imbaro (Chieti), Italy
² Laboratory of Microbiological Control, All-Russian Institute for Plant Protection, Russian Academy of Agricultural Sciences, Shosse Podbelskogo, 3, 189620, St. Petersburg-Pushkin, Russia
³ Laboratory of Renal Physiology, Sechenov Institute of Evolutionary Physiology and Biochemistry, 44 Moris Torez Prospekt, St. Petersburg, Russia
⁴ Institute of Histology and Embryology, University of Vienna, Schwarzspanierstrafle 17, A-1090 Vienna, Austria
⁵ Institute of Cytology, Russian Academy of Sciences, Tikhoretsky Av., 4, 194064, St. Petersburg, Russia

Author for correspondence (e-mail: mironov{at}negrisud.it)

Accepted 10 January 2007

Microsporidia are obligatory intracellular parasites, most species of which live in the host cell cytosol. They synthesize and then transport secretory proteins from the endoplasmic reticulum to the plasma membrane for formation of the spore wall and the polar tube for cell invasion. However, microsporidia do not have a typical Golgi complex. Here, using quick-freezing cryosubstitution and chemical fixation, we demonstrate that the Golgi analogs of the microsporidia Paranosema (Antonospora) grylli and Paranosema locustae appear as 300-nm networks of thin (25- to 40-nm diameter), branching or varicose tubules that display histochemical features of a Golgi, but that do not have vesicles. Vesicles are not formed even if membrane fusion is inhibited. These tubular networks are connected to the endoplasmic reticulum, the plasma membrane and the forming polar tube, and are positive for Sec13, COP and analogs of giantin and GM130. The spore-wall and polar-tube proteins are transported from the endoplasmic reticulum to the target membranes through these tubular networks, within which they undergo concentration and glycosylation. We suggest that the intracellular transport of secreted proteins in microsporidia occurs by a progression mechanism that does not involve the participation of vesicles generated by coat proteins I and II.

Key words: Golgi, Intracellular transport, COP-I vesicles, Microsporidia

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