Abstract
In eukaryotic cells, mitochondria originated in an α-proteobacterial endosymbiont. Although these organelles harbor their own genome, the large majority of genes, originally encoded in the endosymbiont, were either lost or transferred to the nucleus. As a consequence, mitochondria have become semi-autonomous and most of their processes require the import of nuclear-encoded components to be functional. Therefore, the mitochondrial-specific translation has evolved to be coordinated by mitonuclear interactions to respond to the energetic demands of the cell, acquiring unique and mosaic features. However, mitochondrial-DNA-encoded genes are essential for the assembly of the respiratory chain complexes. Impaired mitochondrial function due to oxidative damage and mutations has been associated with numerous human pathologies, the aging process, and cancer. In this review, we highlight the unique features of mitochondrial protein synthesis and provide a comprehensive insight into the mitonuclear crosstalk and its co-evolution, as well as the vulnerabilities of the animal mitochondrial genome.
Highlights
These organelles harbor their own genome, the large majority of genes, originally encoded in the endosymbiont, were either lost or transferred to the nucleus
According to the archezoan scenario, the mitochondrion evolved from an α-proteobacterial ancestor via symbiosis within a primitive eukaryotic host cell termed an “archezoan.” controversy persists regarding the nature of the proto-eukaryotic host that engulfed the mitochondrion, members of the archezoa were probably primitive protists living as parasites in anaerobic environments and characterized by the absence of recognizable mitochondria [6]
While this modification is highly abundant in mitochondrial RNAs, it is almost absent on cytosolic transfer RNA (tRNA)
Summary
The endosymbiont hypothesis is widely accepted for its ability to explain the mitochondrial origin [1,2]. Complete sequencing of the mitochondrial genome (mtDNA) from several mammalian species revealed that mtDNA is of α-proteobacterial origin and that all extant mtDNAs have originated from the same ancestral bacterial genome [3,4] According to these early sequencing studies, mtDNA encodes a small number (13 in mammals) of protein subunits of the mitochondrial electron transport chain and ATP synthase. An alternative view claiming that the host cell for the mitochondrial endosymbiosis was an archaebacterion is the basis of the “symbiogenesis scenario.”. According to this model, the evolution of the nucleus and the compartmentalization of the eukaryotic cell happened after a single endosymbiotic event [7,8]. Many distinct eukaryotic lineages have adapted to living in low oxygen conditions, and as a result, many of these organisms have evolved mitochondria to function anaerobically [14]
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