The First Eukaryotes Were Fused Cells

ArchaeaFEMS Microbiology Reviews 1998 18 225-236. Forterre, Patrick Institut Pasteur Paris France The universal tree of life an update. Front Microbiol 2015 6 717. Csurds, Miklos University Montreal Quebec Canada Ancestral reconstruction by asymmetric Wagner parsimony over continuous characters and squared parsimony over distributions (in print). 

Mycoplasma cells may fuse with the cells of eukaryotic hosts M. fermentans fused CD4 Molt, and CD4 12E lymphocytes in vitro without visible cytotoxicity [69]. Mycoplasma contamination of human tumor cell cultures is frequent with mycoplasma cells attached to tumor cells [70a, b, 71]. However, M. fermentans, or M. penetrans in embryonic mouse cell cultures activated the rc-related vav proto-oncogene, and induced malignant transformation src, Rous sarcoma vav, sixth letter of the Hebrew alphabet standing for linkage or connection) [72] recently reviewed in [73]. 

The fuselloviruses of crenarchaeota are much less likely to be fusogenic for crenarchaeotic and prokaryotic spheroplasts, than the L3 A. laidlawii phage would be. The cell division mechanisms of crenarchaeota vide supra), especially those of the thanmarchaeon ( miraculous ) Nitrosopumilus maritimus, and eukaryotes are phylogeneticaUy related (by the shared operon cvd ESCRT FtsZ) [42, 43], yet even these ingredients cotrld not have created eukaryotic cells by their presumed 

Pro-apoptodc Bcl-2 famly memben promote and antl-a ioptotlc Bd-2 family memben block mltochondilal cytochrome c release 

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Comment. How the mimivimses and the amoebae re-play the ancient scenarios, is not well understood. It is possible, that the first unicellular eukaryotes encountered those protoviral agents, which were generated from fused viroids, that replicated in preceUular ribozyme-powered ribosomes. These agents transferred their residence into the first cells and there have become intracellular parasites. It is also possible that a cellular domain existed prior to the appearance of the current three domains of life (archaea, prokaryota, eukaryota) and fell victim of extinction. The... 

Pearse and Bretscher (1981) have discussed the role of coated vesicles in membrane synthesis and function. Eukaryotic cells are able to specifically take up macromolecules by absorptive endocytosis. The macromolecules are usually transferred to lyso-somes where they may be degraded. The first stage of the process involves the binding of macromolecules to receptors which are localized in coated pits. The latter are indented sites on the plasma membrane and the coated pit buds into the cytoplasm to form a coated vesicle in which lie the endocytosed macromolecules. The coated vesicle sheds its coat rapidly and the endocytic vesicles fuse with each other. This allows receptors to be returned to the plasma membrane while the contents are transferred to the lyso-somes. In order to explain how lysosomal and plasma membranes remain different, it was suggested that the coated pits are able to accept certain macromolecules while excluding others. The accepted proteins enter the coated pit and were presumed to bind directly or indirectly to clathrin. Clathrin, a 180000-dalton protein on the cytoplasmic face of coated pits, provides the polyhedron skeleton for the coated vesicles. Examples of the use of coated vesicles for mediated endocytosis are in the uptake of low-density lipoprotein from the blood and in humans for the transport of immunoglobulins from the mother to the child. For other mammals such as the rat the antibodies are selectively absorbed from the mother s milk by the intestinal epithelium. Coated vesicles also provide a mechanism for virus transport into cells. 

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