Motility proteins and the origin of the nucleus.
Hypotheses on the origin of eukaryotic cells must account for the origin of the microtubular cytoskeletal structures (including the mitotic spindle, undulipodium/cilium (so-called flagellum) and other structures underlain by the 9(2)+2 microtubular axoneme) in addition to the membrane-bounded nucleus. Whereas bacteria with membrane-bounded nucleoids have been described, no precedent for mitotic, cytoskeletal, or axonemal microtubular structures are known in prokaryotes. Molecular phylogenetic analyses indicate that the cells of the earliest-branching lineages of eukaryotes contain the karyomastigont cytoskeletal system. These protist cells divide via an extranuclear spindle and a persistent nuclear membrane. We suggest that this association between the centriole/kinetosome axoneme (undulipodium) and the nucleus existed from the earliest stage of eukaryotic cell evolution. We interpret the karyomastigont to be a legacy of the symbiosis between thermoacidophilic archaebacteria and motile eubacteria from which the first eukaryote evolved. Mutually inconsistent hypotheses for the origin of the nucleus are reviewed and sequenced proteins of cell motility are discussed because of their potential value in resolving this problem. A correlation of fossil evidence with modern cell and microbiological studies leads us to the karyomastigont theory of the origin of the nucleus.
Dolan
Michael F
MF
Department of Geosciences, University of Massachusetts, Morrill Science Center, Amherst 01003, USA. mdolan@geo.umass.edu
Melnitsky
Hannah
H
Margulis
Lynn
L
Kolnicki
Robin
R
D000818:Animals; D005075:Biological Evolution; D002465:Cell Movement / Q000502:physiology; D002467:Cell Nucleus / Q000502:physiology; D004247:DNA; D005057:Eukaryotic Cells; D008562:Membrane Glycoproteins; D008868:Microtubule Proteins; D008870:Microtubules / Q000502:physiology*; D008938:Mitosis; D011387:Prokaryotic Cells; D008941:Spindle Apparatus; D013559:Symbiosis
D008562:Membrane Glycoproteins; D008868:Microtubule Proteins; D004247:DNA