The ZW Micro-Sex Chromosomes of the Chinese Soft-Shelled Turtle (<i>Pelodiscus sinensis</i>, Trionychidae, Testudines) Have the Same Origin as Chicken Chromosome 15

Abstract

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.

Extension, single-locus conversion and physical mapping of sex chromosome sequences identify the Z microchromosome and pseudo-autosomal region in a dragon lizard, Pogona vitticeps

“…There are very few sex-specific sequences reported for reptiles (Cooper et al, 1997;Halverson and Spelman, 2002), although repetitive satellite sequences are known to be interspersed throughout the chromosomes of snakes in high copy number (Singh et al, 1976(Singh et al, , 1980 and are concentrated in particularly high density on the W chromosome (Solari, 1994). A number of functional genes have recently been mapped to the Z and W chromosomes of three snakes, a gecko and a turtle (Matsubara et al, 2006;Kawaia et al, 2007;Kawagoshi et al, 2009).…”

The origin and differentiation process of X and Y chromosomes of the black marsh turtle (Siebenrockiella crassicollis, Geoemydidae, Testudines)

“…This linkage has also been extensively conserved in human chromosome 11 and 14 for eight genes (CPT1A, CRY2, CTR9, DDB1, DEAF1, EIF4G2, ST5, WT1) and five genes (DYNC1H1, GARNL1, PAPOLA, PSMC1, PYGL), respectively, although only BUB1B is localized to human chromosomes 15 (National Center for Biotechnology Information, http://www.ncbi.nlm.nih.gov/). The genetic linkage of S. crassicollis X and Y chromosomes therefore have been highly conserved in amniotes; however, S. crassicollis XY sex chromosomes have no homology with the ZW sex chromosomes of P. sinensis, which is homologous to chicken chromosome 15 (Kawagoshi et al 2009), suggesting that their sex chromosomes were differentiated independently within the same order from different autosomes of the common ancestor. The eastern long-necked turtle (C. longicollis) of Chelidae has micro-XY sex chromosomes, which are detectable by C banding, reverse fluorescent staining, or comparative genomic hybridization (Ezaz et al 2006).…”

“…The sex chromosomes of E. macquarii are considered to have been established by a translocation of an ancestral Y microchromosome as found in the species of a sister clade, C. longicollis, onto the tip of the fourth largest autosome (Martinez et al 2008); however, the origins of the sex chromosomes of these species and their homologies have been still unknown except for the ZW micro-sex chromosomes of P. sinensis. Comparative gene mapping between P. sinensis and chicken revealed that the six largest chromosomes were almost equivalent between two species (Matsuda et al 2005); however, P. sinensis Z chromosome was homologous to chicken chromosome 15 but not to the chicken Z chromosome (Kawagoshi et al 2009). This result suggests that the ZW-type sex chromosomes of birds and turtles differentiated independently in each lineage from different autosome pairs of the common ancestor of Arcosauromorpha, which diverged around 250 million years ago (MYA) (Kumazawa and Nishida 1999;Janke et al 2001;Rest et al 2003;Iwabe et al 2005).…”

“…We revealed that the ZW sex chromosomes of P. sinensis correspond to chicken chromosome 15 (Kawagoshi et al 2009); however, the origins of the testudinian XY sex chromosomes are still unknown. In this study, to elucidate the origin and differentiation process of S. crassicollis XY chromosomes, we first conducted chromosome painting with chromosome-specific DNA probes from P. sinensis, and then performed chromosome mapping of S. crassicollis homologues of chicken genes located on the chromosome that is homologous to S. crassicollis XY chromosomes.…”

Um estudo de caso ligado ao sexo em Python regius (Serpentes: Boidae), com novas ideias sobre a determinação sexual em Henophidia

“…However, the pleurodont X and Y sex chro mosomes are microchromosomes, and seve ral (currently unplaced) genomic scaffolds of Burmese Pythons (e.g., NW_006532210.1, NW_006532455.1, NW_006534197.1, NW_006532240.1, NW_ homology with the pleurodont X chromosome (Castoe et al 2013, Rovatsos et al 2014a; incidentally, this pleurodont sex chromosome maps to a chicken microchromosome, an autosome assigned as chromosome 15, which also shares homology with the documented Z and W sex chromosomes of the Chinese Soft-shelled Turtle (Pelodiscus sinensis) (Kawagoshi et al 2009, Rovatsos et al 2014a.…”