Kawagoshi T, Uno Y, Matsubara K, Matsuda Y, Nishida C
Laboratory of Animal Cytogenetics, Biosystems Science Course, Graduate School of Life Science, Sapporo, Japan.
Cytogenet Genome Res. 2009;125(2):125-31. doi: 10.1159/000227837. Epub 2009 Aug 31.
The Chinese soft-shelled turtle (Pelodiscus sinensis, Trionychidae, Testudines) has ZZ/ZW-type micro-sex chromosomes where the 18S-28S ribosomal RNA genes (18S-28S rDNA) are located. The W chromosome is morphologically differentiated from the Z chromosome by partial deletion and amplification of 18S-28S rDNA and W-specific repetitive sequences. We recently found a functional gene (TOP3B) mapped on the P. sinensis Z chromosome, which is located on chicken (Gallus gallus, GGA) chromosome 15. Then we cloned turtle homologues of 4 other GGA15-linked genes (GIT2, NF2, SBNO1, SF3A1) and localized them to P. sinensis chromosomes. The 4 genes all mapped on the Z chromosome, and 2 of them (SBNO1, SF3A1) were also localized to the W chromosome. Our mapping data suggest that at least one large inversion occurred between GGA15 and the P. sinensis Z chromosome, and that there are homologous regions in the distal portions of both the short and long arms between the Z and W chromosomes. W chromosomal differentiation in P. sinensis probably proceeded by the deletion of the proximal chromosomal region followed by 18S-28S rDNA amplification, after a paracentric inversion occurred at the breakpoints between the distal region of 18S-28S rDNA and the proximal region of SBNO1 on the Z chromosome.
中华鳖（Pelodiscus sinensis，鳖科，龟鳖目）具有ZZ/ZW型微小性染色体，18S - 28S核糖体RNA基因（18S - 28S rDNA）位于其上。W染色体在形态上与Z染色体不同，其18S - 28S rDNA和W特异性重复序列存在部分缺失和扩增。我们最近发现一个功能基因（TOP3B）定位在中华鳖的Z染色体上，该染色体位于鸡（Gallus gallus，GGA）的15号染色体上。然后我们克隆了其他4个与GGA15连锁基因（GIT2、NF2、SBNO1、SF3A1）的鳖同源基因，并将它们定位到中华鳖染色体上。这4个基因都定位在Z染色体上，其中2个基因（SBNO1、SF3A1）也定位到了W染色体上。我们的定位数据表明，在GGA15和中华鳖Z染色体之间至少发生了一次大的倒位，并且在Z和W染色体的短臂和长臂的远端部分存在同源区域。中华鳖W染色体的分化可能是在Z染色体上18S - 28S rDNA远端区域与SBNO1近端区域之间的断点处发生臂间倒位后，先删除近端染色体区域，随后进行18S - 28S rDNA扩增。
