Abstract
AbstractBoth the process and origin of genome reorganization, in which germline genomes are transformed into somatic genomes, are enigmatic. In ciliates, ubiquitous microbial eukaryotes with both somatic and germline nuclei in the same cell, tens of thousands of internally eliminated sequences (IESs) are excised during somatic genome formation. Blepharisma represents one of the two earliest diverging ciliate classes, and has unique, dual pathways of somatic nuclear development, making it ideal for investigating the functioning, origins and evolution of these processes. Here, we report the somatic genome assembly of Blepharisma stoltei strain ATCC 30299 (41 Mb), arranged as numerous alternative telomere-capped minichromosomes, tens to hundreds of kilobases long. This genome encodes eight PiggyBac transposase homologs liberated from transposons. All are subject to purifying selection, but just one, the putative IES excisase, has a complete catalytic amino acid triad. We propose that PiggyBac homologs may have been ancestral excisases that enabled extensive genome reorganization.
Publisher
Cold Spring Harbor Laboratory
Cited by
3 articles.
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