Chromosome Research

, Volume 19, Issue 5, pp 635–644 | Cite as

Additional copies of CBX2 in the genomes of males of mammals lacking SRY, the Amami spiny rat (Tokudaia osimensis) and the Tokunoshima spiny rat (Tokudaia tokunoshimensis)

  • Asato Kuroiwa
  • Sanae Handa
  • Chigusa Nishiyama
  • Eriko Chiba
  • Fumio Yamada
  • Shintaro Abe
  • Yoichi Matsuda


Tokudaia osimensis (the Amami spiny rat) and Tokudaia tokunoshimensis (the Tokunoshima spiny rat) have a sex chromosome composition of XO/XO, no Y chromosome. The mammalian sex-determining gene, SRY, is also absent in these species, which indicates that these spiny rats exhibit a novel sex-determining mechanism that is independent of SRY. To identify a candidate gene that controls this mechanism, the copy numbers and chromosomal locations of 10 genes with important functions in gonadal differentiation were determined: ATRX, CBX2 (M33), DMRT1, FGF9, NR0B1 (DAX1), NR5A1 (Ad4BP/SF1), RSPO1, SOX9, WNT4, and WT1. Multiple bands were detected for NR0B1 in Southern blot analysis, which suggested the presence of multiple copies of the gene in the genomes of these two species. CBX2 was localized to two loci in both sexes of the two species by fluorescence in situ hybridization mapping: 3q24 and 6p11.2 in T. osimensis and 10q25–q26 and 14q12–q13.1 in T. tokunoshimensis. Quantification of copy numbers in the two species by quantitative real-time PCR indicated that there were two or three more copies of CBX2 per haploid genome in males (T. osimensis, n = 3; T. tokunoshimensis, n = 2) than in females (T. osimensis, n = 4; T. tokunoshimensis, n = 2), whereas NR0B1 was present as a single copy in both. The results suggest that additional copies of CBX2 in males might be involved in a novel sex-determining mechanism in species that lack SRY.


sex determination sex differentiation XO Y chromosome 



Alkaline phosphatase


American Standards Association


Bovine serum albumin




Complementary DNA


Cytidine diphosphate




Deoxyuridine 5-triphosphate


Fluorescence in situ hybridization


Immunoglobulin G


International Union for Conservation of Nature


Kilo base pairs




Minimal essential medium


Quantitative real-time PCR


Rapid amplification of cDNA ends


Standard deviation


Sodium dodecyl sulfate


Saline sodium citrate


Untranslated region





The authors thank T. Hashimoto for capturing animals, C. Nishida-Umehara and K. Matsubara for help with cell culture and FISH, K. Morohashi for providing the mouse cDNA clones, and Y. Katoh-Fukui for helpful advises. This work was supported by a Grant-in-Aid for Scientific Research on Priority Areas (no. 16086201) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and a grant from the Naito Foundation, Japan.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Asato Kuroiwa
    • 1
    • 5
  • Sanae Handa
    • 1
  • Chigusa Nishiyama
    • 1
  • Eriko Chiba
    • 1
  • Fumio Yamada
    • 2
  • Shintaro Abe
    • 3
  • Yoichi Matsuda
    • 4
  1. 1.Graduate School of Life ScienceHokkaido UniversitySapporoJapan
  2. 2.Forestry and Forest Products Research InstituteTsukubaJapan
  3. 3.Naha Nature Conservation Office, Ministry of the EnvironmentNahaJapan
  4. 4.Laboratory of Animal Genetics, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural SciencesNagoya UniversityNagoyaJapan
  5. 5.Laboratory of Animal Cytogenetics, Faculty of ScienceHokkaido UniversitySapporoJapan

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