Functional and evolutionary analysis of a eukaryotic parasitic genome

Covariation of Mitochondrial Genome Size with Gene Lengths: Evidence for Gene Length Reduction During Mitochondrial Evolution

“…In most bacterial genomes deletions are more common than insertions (Mira et al 2001), which could lead to a net reduction in gene length. As mentioned in the Introduction, gene shortening in obligate intracellular symbionts has been documented in a number of cases (Cavalier-Smith 2002;Charles et al 1999;Vivares et al 2002;Wernegreen 2002). The taxonomic distribution of these symbionts indicates that gene shortening evolved several times independently.…”

“…It has been suggested that this might be caused by the high AT content of the genome and by a mutational bias for deletions. Dramatic shortening of coding regions has also been observed in the obligate intracellular parasite Encephalitozoon cuniculi: 85% of its proteins are on average 14.6% smaller than their yeast homologs (Vivares et al 2002). Likewise, unusual short protein coding genes are found in the vestigial nuclear genomes of the nucleomorphs of cryptomonads (Cavalier-Smith 2002).…”

“…Gene shortening in small genomes has been observed in a number of obligate intracellular symbionts (parasitic and mutualistic) including diverse groups such as symbiotic bacteria (Buchnera) in aphids (Charles et al 1999), a microsporidium infecting humans (Vivares et al 2002), and the vestigial nuclear genomes of the nucleomorphs of cryptomonads (Cavalier-Smith 2002). It has been suggested that the reductions of gene lengths and genome size which are observed in all these organisms are a consequence of their intimate symbiotic life style (Wernegreen 2002).…”

Simplicity and Complexity of Microsporidian Genomes

“…The distribution of the E. cuniculi genes among functional categories shows that gene loss is not random. Instead, absent genes represent complete metabolic or regulatory pathways (28,61). As the organism becomes host dependent, some metabolic functions are provided by the host cell, so genes involved in such functions may become redundant and lost after inactivation by mutation.…”

Shrink it or lose it: balancing loss of function with shrinking genomes in the microsporidia

“…Direct biochemical analyses are hampered by their obligate intracellular nature, 14 but in the species where we have abundant sequence data, the metabolism can be modeled based on what genes are present. 15,16 In all such species, many small molecule biosynthetic pathways are completely absent, and core carbon metabolism is limited to glycolysis, the pentose phosphate pathway, and synthesis and degradation of the storage carbohydrate trehalose-even the smallest E. intestinalis genome has the full complement of genes for these pathways. 7 In Enterocytozoon bieneusi, however, virtually all these genes have been lost.…”