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Microbiol. Rev., 12 1996, 697-721, Vol 60, No. 4
B Becker and M Melkonian
All cells secrete a diversity of macromolecules to modify their environment
or to protect themselves. Eukaryotic cells have evolved a complex secretory
pathway consisting of several membrane-bound compartments which contain
specific sets of proteins. Experimental work on the secretory pathway has
focused mainly on mammalian cell lines or on yeasts. Now, some general
principles of the secretory pathway have become clear, and most components
of the secretory pathway are conserved between yeast cells and mammalian
cells. However, the structure and function of the secretory system in
protists have been less extensively studied. In this review, we summarize
the current knowledge about the secretory pathway of five different groups
of protists: Giardia lamblia, one of the earliest lines of eukaryotic
evolution, kinetoplastids, the slime mold Dictyostelium discoideum, and two
lineages within the "crown" of eukaryotic cell evolution, the alveolates
(ciliates and Plasmodium species) and the green algae. Comparison of these
systems with the mammalian and yeast system shows that most elements of the
secretory pathway were presumably present in the earliest eukaryotic
organisms. However, one element of the secretory pathway shows considerable
variation: the presence of a Golgi stack and the number of cisternae within
a stack. We suggest that the functional separation of the plasma membrane
from the nucleus- endoplasmic reticulum system during evolution required a
sorting compartment, which became the Golgi apparatus. Once a Golgi
apparatus was established, it was adapted to the various needs of the
different organisms.
Copyright © 1996, American Society for Microbiology
The secretory pathway of protists: spatial and functional organization and evolution
Botanisches Institut, Universitat zu Koln, Germany. bbecker@biolan.uni- koeln.de
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