RESUMO
Genome sequences have been determined for many model organisms; however, repetitive regions such as centromeres, telomeres, and subtelomeres have not yet been sequenced completely. Here, we report the complete sequences of subtelomeric homologous (SH) regions of the fission yeast Schizosaccharomyces pombe. We overcame technical difficulties to obtain subtelomeric repetitive sequences by constructing strains that possess single SH regions of a standard laboratory strain. In addition, some natural isolates of S. pombe were analyzed using previous sequencing data. Whole sequences of SH regions revealed that each SH region consists of two distinct parts with mosaics of multiple common segments or blocks showing high variation among subtelomeres and strains. Subtelomere regions show relatively high frequency of nucleotide variations among strains compared with the other chromosomal regions. Furthermore, we identified subtelomeric RecQ-type helicase genes, tlh3 and tlh4, which add to the already known tlh1 and tlh2, and found that the tlh1-4 genes show high sequence variation with missense mutations, insertions, and deletions but no severe effects on their RNA expression. Our results indicate that SH sequences are highly polymorphic and hot spots for genome variation. These features of subtelomeres may have contributed to genome diversity and, conversely, various diseases.
Assuntos
Variação Genética , Genoma Fúngico , Schizosaccharomyces/genética , Telômero/genética , Sequência de Bases , Mutação INDEL/genética , Mosaicismo , Família Multigênica , Nucleotídeos/genética , Filogenia , RNA Fúngico/genética , RecQ Helicases/genética , Schizosaccharomyces/isolamento & purificaçãoRESUMO
Centromeres play crucial roles in faithful chromosome segregation and genome integrity. In simian primates, centromeres possess tandem array of alpha satellite DNA (also referred to as alphoid DNA). Average sizes of alpha satellite repeat units vary between species, for example, 171 bp in human and 343-344 bp in many platyrrhini species (New World monkeys). Interestingly, Azara's owl monkey (Aotus azarae), a platyrrhini species, possesses alpha satellite DNA of two distinct unit sizes, OwlAlp1 (185 bp) and OwlAlp2 (344 bp), both of which present as megasatellite DNAs in the genome. It is, however, unknown which repeat sequence is responsible for functional centromere formation. To investigate the localization of centromeres in vivo, we carried out chromatin immunoprecipitation (ChIP) assay using Azara's owl monkey cells. We found that CENP-A, a histone H3 variant essential for centromere formation, was enriched at OwlAlp1, but not at OwlAlp2. Moreover, CENP-A was detected only at constricted regions of chromosomes by immunofluorescent microscopy. In contrast, trimethylation of histone H3-K9 (H3K9me3), a marker of heterochromatin, was enriched at both OwlAlp1 and OwlAlp2. Our results show that the shorter alpha satellite repeat, OwlAlp1, is selectively used for centromere formation in this monkey.
