Chapter 8 : Cell Biology of the Chlamydial Inclusion

Early events in nascent inclusion biogenesis. Soon after chlamydial entry, the nascent inclusion rapidly loses plasma membrane and early endocytic and classic endolysosomal markers ( Scidmore et al., 2003 ), including the phosphoinositides PI(4,5)P2 and PI3P and endolysosomal Rabs (Rab5, Rab7, and Rab9) ( Moorhead et al., 2010 ; Rzomp et al., 2003 ). Recycling endosomes and their associated Rabs localize to early inclusions ( Rzomp et al., 2006 , 2003 ) and may facilitate migration to the MTOC, in a microtubule- and dynein-dependent manner ( Clausen et al., 1997 ). p150(Glued), the component of the dynactin protein complex linking vesicular cargo to dynein, is required for migration to the MTOC, although p50 dynamitin is not ( Grieshaber et al., 2003 ). Chlamydia inclusion membrane proteins IncB and Ct850 are postulated to play a role in this interaction to promote association of the nascent inclusion with the microtubule-organizing center ( Mital et al., 2010 ). Endocytic pathway-associated SNAREs, including Vamp3, -7, and -8, localize around the inclusion in a fusion-inhibited state potentially as a result of interactions with Chlamydia Incs (IncA, CT813, and CT223) ( Delevoye et al., 2008 ; Paumet et al., 2009 ). These Inc proteins have been proposed to function as inhibitory SNARE (iSNARE) mimics ( Paumet et al., 2009 ). doi:10.1128/9781555817329.ch8.f1

The inclusion interacts with multiple subcellular compartments. Fragmented Golgi apparatus ministacks, the ER, LDs, mitochondria, and recycling endosomes (RE) closely associate with the inclusion ( Heuer et al., 2009 ; Peterson and de la Maza, 1988 ; Kumar et al., 2006 ; Matsumoto et al., 1991 ; van Ooij et al., 1997 ; Scidmore et al., 1996 ). These interactions may facilitate nutrient acquisition directly from these organelles. Golgi apparatus fragmentation enhances sphingolipid uptake ( Heuer et al., 2009 ), and lipid droplets translocate into the lumen of the inclusion ( Cocchiaro et al., 2008 ). Additional pathways for lipid delivery (inset) include vesicular transport of Golgi apparatus-derived exocytic vesicles ( Hackstadt et al., 1996 ; Carabeo et al., 2003 ), MVBs ( Beatty, 2008 , 2006 ), and transfer at membrane contact sites (MCS) between the ER and inclusion membranes ( Derré et al., 2011 ; Elwell et al., 2011 ). The inclusion remains in close association with centrosomes at the MTOC throughout intracellular infection ( Grieshaber et al., 2006 ). doi:10.1128/9781555817329.ch8.f2