Multiple Sex Chromosome System X1X2Y in African Killifish Genera Nothobranchius and Fundulosoma (Cyprinodontiformes)
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1
Severtsov Institute of Ecology and Evolution (RAS), Russia
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2
Vavilov Institute of General Genetics, Russian Academy of Sciences, Russia
In contrast to amniotes, heteromorphic sex chromosomes in fishes have been found in about only 10% of species investigated. Many independent groups of fishes show evidence for sex chromosome turnover and formation of multiple sex chromosome systems [Kitano, Peichel, 2012]. African annual killifish genus Nothobranchius is a convenient model for sex chromosome evolution and turnover studies. This genus includes 76 valid species and has one of the most variable diploid number of chromosomes among all other genera of vertebrates. It ranges from 2n = 16 (NF = 30) in N. rachovii to 2n = 50/49 (female/male; NF = 50) in N. brieni. This dramatic variation of karyotypes in Nothobranchius species may be related to extreme conditions in their natural habitat, ephemeral pools in East Africa. In the majority of species from this genus, heteromorphic sex chromosomes were not detected with the conventional methods of cytogenetics. However, a multiple sex chromosome system X1X1X2X2/X1X2Y was found in the following 5 species, in which males have one chromosome less than females: N. lourensi (2n=28/27), N. guentheri (2n=36/35), N. janpapi (2n=38/37), N. ditte (2n=40/39) and N. brieni (2n=50/49). Genus Fundulosoma is closely related to genus Nothobranchius and represented by one species – F. thierry with 2n = 44/43 (also X1X2Y sex chromosome system) [Krysanov, Demidova, Nagy, 2016; Krysanov, Demidova, 2018].
In present study, we investigated prophase I of meiosis in all Nothobranchius and Fundulosoma species with X1X2Y sex chromosome system (N. lourensi, N. guentheri, N. janpapi, N. ditte, N. brieni and F. thierry) using synaptonemal complex analysis. In male spermatocytes of all this species X1X2Y sex trivalents were detected in prophase I of meiosis. We employed transmission electron microscopy, immunofluorescence analysis with antibodies against proteins SYCP3 (lateral elements of synaptonemal complex) and MLH1 (a meiotic recombination marker), as well as fluorescent in situ hybridization with a telomere probe to describe X1X2Y sex trivalents. Comparative analysis of sex trivalents structure (rank, length, X1/X2 ratio, MLH1 distribution, etc.) and molecular phylogenetic data for genus Nothobranchius and Fundulosoma suggest that multiple sex chromosome system X1X1X2X2/X1X2Y emerged independently at least in some of these species and that neo-Y chromosome emerged due to fusion between ancestral Y chromosome (with X1 as a homologue) and autosome (X2).
Acknowledgements
The reported study was funded by RFBR according to the research project № 18-34-00638.
References
Kitano, J., & Peichel, C. L. (2012). Turnover of sex chromosomes and speciation in fishes. Environmental Biology of Fishes, 94(3), 549–558. https://doi.org/10.1007/s10641-011-9853-8
Krysanov, E., Demidova, T., & Nagy, B. (2016). Divergent karyotypes of the annual killifish genus Nothobranchius (Cyprinodontiformes, Nothobranchiidae). Comparative Cytogenetics, 10(3), 439–445. https://doi.org/10.3897/CompCytogen.v10i3.9863
Krysanov, E., & Demidova, T. (2018). Extensive karyotype variability of African fish genus Nothobranchius (Cyprinodontiformes). Comparative Cytogenetics, 12(3), 387–402. https://doi.org/10.3897/CompCytogen.v12i3.25092
Keywords:
Cytogenetics,
Meiosis,
Synaptonemal Complex,
Sex Chromosomes,
Multiple sex chromosome system,
Nothobranchius
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Poster
Topic:
GENETICS, GENOMICS AND PHYSIOLOGY
Citation:
Simanovsky
SA,
Demidova
TB,
Spangenberg
VE,
Matveevsky
SN,
Ordzhonikidze
KG,
Kolomiets
OL and
Krysanov
EY
(2019). Multiple Sex Chromosome System X1X2Y in African Killifish Genera Nothobranchius and Fundulosoma (Cyprinodontiformes).
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00158
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Received:
07 Jun 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
PhD. Sergey A Simanovsky, Severtsov Institute of Ecology and Evolution (RAS), Moscow, Russia, sergeysimanovsky@gmail.com