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Review
. 1998 Mar 23;140(6):1277-80.
doi: 10.1083/jcb.140.6.1277.

Cruising along microtubule highways: how membranes move through the secretory pathway

G S Bloom  1 , L S Goldstein
Affiliations
Review

Cruising along microtubule highways: how membranes move through the secretory pathway

G S Bloom et al. J Cell Biol. .

Erratum in

  • J Cell Biol 1998 May 18;141(4):1095
No abstract available

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Figures

Figure 1
Figure 1
A model for MT functions in secretion. Black and purple arrows indicate MT-dependent and -independent transport steps, respectively. (1) Many cells normally contain radially arranged MTs oriented with their plus (+) ends distal to a perinuclear MTOC. In such cells, the IC moves along MTs bidirectionally between the peripheral ER and a centrally located Golgi, which comprises cis (c), medial (m), and trans (t) stacks and the TGN. Segregation of ER from Golgi depends on the polarized, radial arrangement of MTs and a balance between Golgi-directed membrane flow toward MT minus ends and ER-directed flow toward MT plus ends. Secretory vesicles also travel along MTs, toward their plus ends, from the TGN to the plasma membrane. Transport from ER to IC involves COP II–coated structures that move independently of MTs. IC membranes are coated with COP I for ER-to-Golgi transport, but whether they retain COP I coats for Golgi-to-ER transport has not been reported. (2) Membrane budding from the ER and Golgi continues after MT disassembly by nocodazole (9, 10). Until a significant amount of membrane has exited the Golgi, it remains largely intact near the cell center. During this time window, delivery of ER-derived material to the Golgi must occur by diffusion and is inefficient because of the substantial distance that separates most of the ER from the Golgi (9, 11). Consequently, Golgi-dependent protein processing and secretion are inhibited (9, 28, 32). (3) In the prolonged absence of MTs, Golgi components that may have cycled through the ER (9, 10) accumulate near ER exit sites and IC membranes through which they might have passed, and miniature Golgi stacks are found throughout the cytoplasm (30). The lack of MTs prevents movement of these stacks and the IC toward the MTOC. Nevertheless, the short distances that separate ER, IC, and Golgi under these circumstances permit efficient, diffusion-mediated transfer of materials among them and allow Golgi- dependent protein processing and secretion to proceed. Secretory vesicles may reach the cell surface by diffusion, but directionally biased secretion is prevented as long as MTs are absent (31). (4) Soon after nocodazole is removed, Golgi ministacks travel toward the MTOC and eventually reestablish a centrally located Golgi complex (15) that supports directionally biased secretion.
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References

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