Cross-species chromosome painting in the Perissodactyla: delimitation of homologous regions in Burchell’s zebra <i>(Equus burchellii)</i> and the white <i>(Ceratotherium simum)</i> and black rhinoceros <i>(Diceros bicornis)</i>

Abstract

Conserved chromosomal segments in the black rhinoceros, Diceros bicornis (DBI, 2n = 84), and its African sister-species the white rhinoceros, Ceratotherium simum (CSI, 2n = 82), were detected using Burchell’s zebra (Equus burchellii, EBU, 2n = 44) chromosome-specific painting probes supplemented by a subset of those developed for the horse (Equus caballus, ECA, 2n = 64). In total 41 and 42 conserved autosomal segments were identified in C. simum and D. bicornis respectively. Only 21 rearrangements (20 fissions and 1 fusion) are necessary to convert the Burchell’s zebra karyotype into that of the white rhinoceros. One fission distinguishes the D. bicornis and C. simum karyotypes which, excluding heterochromatic differences, are identical in all respects at this level of resolution. Most Burchell’s zebra chromosomes correspond to two rhinoceros chromosomes although in four instances (EBU18, 19, 20 and 21) whole chromosome synteny has been retained among these species. In contrast, one rhinoceros chromosome (DBI1, CSI1) comprises two separate Burchell’s zebra chromosomes (EBU11 and EBU17). In spite of the high diploid numbers of the two rhinoceros species their karyotypes are surprisingly conserved offering a glimpse of the putative ancestral perissodactyl condition and a broader understanding of genome organization in mammals.

Multidirectional cross-species painting illuminates the history of karyotypic evolution in Perissodactyla

“…Human homologies that were not found in these experiments but that are inferred from previously published data ) are indicated by circles. segments in at least one of the three perissodactyl families; the acrocentric chromosome ECA 15 is disrupted into two segments in rhinoceroses; similarly, the fragmentation of ECA 4 in DBI accounts for the difference in 2n between CSI and DBI, as was previously demonstrated (Trifonov et al 2003, Robinson et al 2005. In total, the 31 ECA chromosomes delimit 42 evolutionarily conserved segments in Perissodactyla (if we discard the ECA4/31 inversion in donkey chromosome 1, Yang et al 2004); 74 combinations of evolutionarily conserved ECA segments are also revealed (Supplementary Table S1).…”

“…The chromosomes of white and black rhinoceroses were arranged according to Trifonov et al (2003), while the chromosomes of Malayan tapir and the first 15Y20 large chromosomal pairs of the New World tapirs were arranged according to GTG-banded karyotypes published by Houck et al (2000). The remaining smaller autosomes of the New World tapirs were arranged largely according to their size, from the largest to the smallest.…”

“…When the project was initiated at the Institute of Cytology and Genetics (Novosibirsk), only painting probes from T. indicus, E. grevyi, and human were available to the Novosibirsk laboratory. Malayan tapir paints were first hybridized onto metaphases of Burchell_s zebra and black rhinoceros, two species that have previously been studied using probes from human, horse, and Burchell_s zebra (Trifonov et al 2003, Robinson et al 2005, as well as to onager and Grevy_s zebra, two species that have not previously been studied by chromosome painting. Only Grevy_s zebra probes were hybridized onto chromosomes of onager.…”

“…Most recently, Musilova et al (2007) reinvestigated the karyotypic relationships among E. grevyi, E. burchelli and domestic horse using horse chromosome arm-specific probes. In Ceratomorpha, only the black and white rhinoceroses were studied by comparative chromosome painting using probes from Burchell_s zebra (Trifonov et al 2003, Robinson et al 2005.…”

Karyotypic relationships among Equus grevyi, Equus burchelli and domestic horse defined using horse chromosome arm-specific probes

“…Furthermore, E. burchelli probes have been employed for the comparison of karyotypes in some members of rhinoceros (Trifonov et al 2003), which belong to the same order as Equidae.…”