Archaeal Origins of Eukaryotic Cell and Nucleus.

Symbiosis is a major evolutionary force, especially at the cellular level. Here we discuss several older and new discoveries suggesting that besides mitochondria and plastids, eukaryotic nuclei also have symbiotic origins. We propose an archaea-archaea scenario for the evolutionary origin of the eukaryotic cells. We suggest that two ancient archaea-like cells, one based on the actin cytoskeleton and another one based on the tubulin-centrin cytoskeleton, merged together to form the first nucleated eukaryotic cell. This archaeal endosymbiotic origin of eukaryotic cells and their nuclei explains several features of eukaryotic cells which are incompatible with the currently preferred autogenous scenarios of eukaryogenesis.

Energide-cell body as smallest unit of eukaryotic life.

Background: The evolutionary origin of the eukaryotic nucleus is obscure and controversial. Currently preferred are autogenic concepts; ideas of a symbiotic origin are mostly discarded and forgotten. Here we briefly discuss these issues and propose a new version of the symbiotic and archaeal origin of the eukaryotic nucleus. Scope and Conclusions: The nucleus of eukaryotic cells forms via its perinuclear microtubules, the primary eukaryotic unit known also as the Energide-cell body. As for all other endosymbiotic organelles, new Energides are generated only from other Energides. While the Energide cannot be generated de novo, it can use its secretory apparatus to generate de novo the cell periphery apparatus. We suggest that Virchow's tenet Omnis cellula e cellula should be updated as Omnis Energide e Energide to reflect the status of the Energide as the primary unit of the eukaryotic cell, and life. In addition, the plasma membrane provides feedback to the Energide and renders it protection via the plasma membrane-derived endosomal network. New discoveries suggest archaeal origins of both the Energide and its host cell.

Thomas Kuhn is alive and well: the evolutionary relationships of simple life form--a paradigm under siege ?

A Kuhnian framework is used to analyze the current controversy over whether two or three fundamental types of life forms exist. Until the 1980s, all life was classified into two primary forms: eukaryotes and prokaryotes. Using molecular sequencing data, Carl Woese suggested the archaebacteria constituted a third domain. In the mid-1990s, Radhey S. Gupta challenged the three-domain hypothesis. While this dispute may seem to be a purely technical debate over the analysis of protein and nucleic acid sequence data, the controversy encompasses broader issues such as the aims of classification and the role of microorganisms in the biosphere. At the heart of this dispute is what kinds of data are relevant to constructing an overall taxonomy. The prestige of molecular biology played a large role in why the three-domain hypothesis was accepted so readily, but supporters of the two-domain hypothesis argue that the fossil record, morphology, and cell physiology should all play a role in taxonomy. This case study provides a good example of a paradigm shift in the making, demonstrating that issues beyond the raw data will be significant factors in deciding whether the three-domain hypothesis will prevail or a new classificatory scheme will emerge.