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

Kira S Zadesenets,Irina D Konopatskaia,Aline Schlatter,Dita B Vizoso,Nikolay B Rubtsov,Lukas Schärer,Eugene Berezikov,Riccardo Castiglia

doi:10.1371/journal.pone.0164915

Kira S Zadesenets, Irina D Konopatskaia + Show 6 more

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https://doi.org/10.1371/journal.pone.0164915

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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.

Highlights

Making progress in our understanding of biological processes often depends on the availability of suitable experimental model organisms
We found that Macrostomum sp. 8 has a karyotype similar to that of M. lignano, with tetrasomy for its largest chromosome being the dominant karyotype, while the other two species have karyotypes that are more typical of the genus Macrostomum
When we view the karyotype data assembled by Egger and Ishida [18] together with the karyotype data presented here in the context of the current Macrostomum molecular phylogeny [13], it appears very probable that the karyotype of M. lignano has evolved from a 2n = 6 karyotype

Summary

Introduction

Making progress in our understanding of biological processes often depends on the availability of suitable experimental model organisms. The free-living flatworm Macrostomum lignano (Platyhelminthes, Rhabditophora) was introduced as a new model organism for research in evolutionary and developmental biology of the Lophotrochozoa [1,2,3] This flatworm is small and transparent, with clearly defined organ systems, and it is cultured under laboratory conditions, making it very convenient for a diversity of research topics. This flatworm has many additional beneficial traits, including a high regenerative potential provided by pluripotent stem cells, the so-called neoblasts [7, 8] These cells permit efficient whole body regeneration after amputation of different body parts [9], and the regeneration process can be studied with functional assays [10, 11]. This inbred line, a transgenic line called HUB1 (established in the DV1 line), and a number of outbred cultures have been successfully maintained for years and used for many studies [1, 13,14,15,16,17]

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