Evidence for Karyotype Polymorphism in the Free-Living Flatworm, Macrostomum lignano, a Model Organism for Evolutionary and Developmental Biology

PLoS One. 2016 Oct 18;11(10):e0164915. doi: 10.1371/journal.pone.0164915. eCollection 2016.

Abstract

Over the past decade, the free-living flatworm Macrostomum lignano has been successfully used in many areas of biology, including embryology, stem cells, sexual selection, bioadhesion and aging. The increased use of this powerful laboratory model, including the establishment of genomic resources and tools, makes it essential to have a detailed description of the chromosome organization of this species, previously suggested to have a karyotype with 2n = 8 and one pair of large and three pairs of small metacentric chromosomes. We performed cytogenetic analyses for chromosomes of one commonly used inbred line of M. lignano (called DV1) and uncovered unexpected chromosome number variation in the form of aneuploidies of the largest chromosomes. These results prompted us to perform karyotypic studies in individual specimens of this and other lines of M. lignano reared under laboratory conditions, as well as in freshly field-collected specimens from different natural populations. Our analyses revealed a high frequency of aneuploids and in some cases other numerical and structural chromosome abnormalities in laboratory-reared lines of M. lignano, and some cases of aneuploidy were also found in freshly field-collected specimens. Moreover, karyological analyses were performed in specimens of three further species: Macrostomum sp. 8 (a close relative of M. lignano), M. spirale and M. hystrix. Macrostomum sp. 8 showed a karyotype that was similar to that of M. lignano, with tetrasomy for its largest chromosome being the most common karyotype, while the other two species showed a simpler karyotype that is more typical of the genus Macrostomum. These findings suggest that M. lignano and Macrostomum sp. 8 can be used as new models for studying processes of partial genome duplication in genome evolution.

MeSH terms

  • Animals
  • Biological Evolution
  • Chromosomes*
  • Cytogenetic Analysis
  • DNA Probes / metabolism
  • In Situ Hybridization, Fluorescence
  • Karyotype
  • Metaphase
  • Platyhelminths / genetics*
  • Platyhelminths / growth & development

Substances

  • DNA Probes

Grant support

The reported study was supported by: (1) the Russian Foundation for Basic Research (RFBR), http://www.rfbr.ru/rffi/eng, Project grant no. 14-04-32007 (KZ); (2) Swiss National Science Foundation (SNSF), http://www.snf.ch/en/Pages/default.aspx, Grant no. 143732 (LS); (3) European Research Council (ERC), https://erc.europa.eu/, Starting Grant no. 310765 (EB); (4) Federal Agency for Science and Innovation, http://fano.gov.ru/en/, grant 0324-2015-0003, Russian Academy of Sciences, http://www.ras.ru/index.aspx (NBR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.