The gene density of eukaryotic nuclear genomes is generally low relative to prokaryotes, but several eukaryotic lineages (many parasites or endosymbionts) have independently evolved highly compacted, gene-dense genomes. The best studied of these are the microsporidia, highly adapted fungal parasites, and the nucleomorphs, relict nuclei of endosymbiotic algae found in cryptomonads and chlorarachniophytes. These systems are now models for the effects of compaction on the form and dynamics of the…

Microsporidia have been known for some time to possess among the smallest genomes of any eukaryote. There is now a completely sequenced microsporidian genome, as well as several other large-scale sequencing efforts, so the nature of these genomes is becoming apparent. This paper reviews some of the characteristics of microsporidian genomes in general, and some of the recent discoveries made through comparative genomic analyses. In general, microsporidian genomes are both reduced and compacted….

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Photoreactivation is the repair of DNA damage induced by ultraviolet light radiation using the energy contained in visible-light photons. The process is carried out by a single enzyme, photolyase, which is part of a large and ancient photolyase/cryptochrome gene family. We have characterised a photolyase gene from the microsporidian parasite, Antonospora locustae (formerly Nosema locustae) and show that it encodes a functional photoreactivating enzyme and is expressed in the infectious spore…

Microsporidian genomes are extraordinary among eukaryotes for their extreme reduction: although they are similar in form to other eukaryotic genomes, they are typically smaller than many prokaryotic genomes. At the same time, their rates of sequence evolution are among the highest for eukaryotic organisms. To explore the effects of compaction on nuclear genome evolution, we sequenced 685,000 bp of the Antonospora locustae genome (formerly Nosema locustae) and compared its organization with the…

Nosema locustae is a microsporidian parasite of grasshopper pests that is used as a biological control agent, and is one of the emerging model systems for microsporidia. Due largely to its diplokaryotic nuclei, N. locustae has been classified in the genus Nosema, a large genus with members that infect a wide variety of insects. However, some molecular studies have cast doubt on the validity of certain Nosema species, and on the taxonomic position of N. locustae. To clarify the affinities of this…

We investigated the relationship between satellite copy number and chromosomal evolution in tuco-tucos (genus Ctenomys), a karyotypically diverse clade of rodents. To explore phylogenetic relationships among 23 species and 5 undescribed forms, we sequenced the complete mitochondrial cytochrome b genes of 27 specimens and incorporated 27 previously published sequences. We then used quantitative dot-blot techniques to assess changes in the copy number of the major Ctenomys satellite DNA (satDNA),…