Zadesenets KS, Rubtsov NB. Regions enriched for DNA repeats in chromosomes of Macrostomum mirumnovem, a species with a recent Whole Genome Duplication.
Vavilovskii Zhurnal Genet Selektsii 2020;
24:636-642. [PMID:
33659849 PMCID:
PMC7716556 DOI:
10.18699/vj20.657]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The free-living flatworm Macrostomum mirumnovem is a neopolyploid species whose genome underwent
a recent Whole Genome Duplication (WGD). In the result of chromosome fusions of the ancient haploid
chromosome set, large metacentric chromosomes were formed. In addition to three pairs of small metacentrics,
the current karyotype of M. mirumnovem contains two pairs of large metacentric chromosomes, MMI1 and MMI2.
The generation of microdissected DNA libraries enriched for DNA repeats followed by DNA probe preparation and
fluorescent in situ hybridization (FISH) were performed. The DNA probes obtained marked chromosome regions
enriched for different DNA repeats in the M. mirumnovem chromosomes. The size and localization of these regions
varied in different copies of large chromosomes. They varied even in homologous chromosomes, suggesting their
divergence due to genome re-diploidization after a WGD. Besides the newly formed chromosome regions enriched
for DNA repeats, B chromosomes were found in the karyotypes of the studied specimens of M. mirumnovem. These
B chromosomes varied in size and morphology. FISH with microdissected DNA probes revealed that some Bs had
a distinct DNA content. FISH could paint differently B chromosomes in different worms and even in the same sample.
B chromosomes could carry a bright specific fluorescent signal or could show no fluorescent signal at all. In latter
cases, the specific FISH signal could be absent even in the pericentromeric region of the B chromosome. Possible
mechanisms of B chromosome formation and their further evolution are discussed. The results obtained indicate
an important role that repetitive DNAs play in genome re-diploidization initiating a rapid differentiation of large
chromosome copies. Taking together, karyotype peculiarities (a high level of intraspecific karyotypic diversity associated
with chromosome number variation, structural chromosomal rearrangements, and the formation of new
regions enriched for DNA repeats) and some phenotypic features of M. mirumnovem (small body size, short lifecycle,
easy maintenance in the laboratory) make this species a perspective model in the studies of genomic and
karyotypic evolution in species passed through a recent WGD event.
Collapse