Analogs of the Golgi complex in microsporidia: structure and avesicular mechanisms of function.
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, gammaCOP 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.
Beznoussenko
Galina V
GV
Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale, 66030 Santa Maria Imbaro (Chieti), Italy.
Dolgikh
Viacheslav V
VV
Seliverstova
Elena V
EV
Semenov
Petr B
PB
Tokarev
Yuri S
YS
Trucco
Alvar
A
Micaroni
Massimo
M
Di Giandomenico
Daniele
D
Auinger
Peter
P
Senderskiy
Igor V
IV
Skarlato
Sergei O
SO
Snigirevskaya
Ekaterina S
ES
Komissarchik
Yan Yu
YY
Pavelka
Margit
M
De Matteis
Maria A
MA
Luini
Alberto
A
Sokolova
Yuliya Ya
YY
Mironov
Alexander A
AA
D000818:Animals; D022181:COP-Coated Vesicles / Q000378:metabolism / Q000648:ultrastructure; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D005216:Fat Body / Q000382:microbiology / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006135:Gryllidae / Q000033:anatomy & histology; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008018:Life Cycle Stages; D016814:Microsporidia / Q000145:classification / Q000254:growth & development* / Q000378:metabolism* / Q000472:pathogenicity / Q000502:physiology / Q000648:ultrastructure; D016881:Microsporidiosis / Q000382:microbiology; D013045:Species Specificity