The choanoflagellate Monosiga brevicollis karyotype revealed by the genome sequence: Telomere-linked helicase genes resemble those of some fungi

摘要

The ～42 Mbp assembled genome sequence for the choanoflagellate Monosiga brevicollis reveals that most of the large scaffolds of 300–2,600 kb represent entire chromosomes or chromosome arms. Telomeres are partially assembled at the termini of 37 scaffolds, while another 43 scaffolds end in telomere-associated regions containing distinctive gene sets. Potential centromeric regions were identified on 39 scaffolds. Together, these observations suggest a karyotype of ～40 metacentric and submetacentric chromosomes averaging 1 Mbp in size. Genes encoding RecQ family DNA helicases, along with ankyrin-domain proteins and serine/threonine kinases, are associated with most telomeres, a feature shared with some fungi. This telomere-linked helicase gene arrangement might be ancestral to both fungi and choanoflagellates in the super-kingdom Opisthokonta; however, the great lability of telomere architecture suggests that it could also be a convergent feature.