Chromosome evolution in bears: reconstructing phylogenetic relationships by cross-species chromosome painting

Abstract

Genome-wide homology maps among dog (Canis familiaris, CFA, 2n = 78), African lion (Panthera leo, PLE, 2n = 38), clouded leopard (Neofelis nebulosa, NNE, 2n = 38) and Malayan sun bear (Helartos malayanus, HMA, 2n = 74) have been established by chromosome painting using a complete set of dog probes. In total, chromosome-specific painting probes from the 38 dog autosomes reveal 69, 69 and 73 conserved segments in African lion, clouded leopard and Malayan sun bear, respectively. The chromosomal painting results show that the African lion and clouded leopard have an identical karyotype which, in turn, is similar to that previously published for the cat (Felis catus, FCA 2n = 38). The findings confirm and extend other studies that show felids to be karyotypically conserved. In contrast, ursids, including the Malayan sun bear, have a relatively highly rearranged karyotype in comparison with other carnivores. The 2n = 74 karyotype of the Malayan sun bear, which is believed to closely resemble the ancestral karyotype of the Ursidae, could have evolved from the 2n = 42 putative ancestral carnivore karyotype by an inversion and 16 centric fissions. Independent fusions of the acrocentric ancestral chromosomes have generated the unique karyotypes of the giant panda and the spectacled bear.

Karyotypic conservatism in the suborder Feliformia (Order Carnivora)

“…All available evidence supports the division of order Carnivora into two monophyletic groups: Feliformia (cats, mongooses, civets and hyenas) and Caniformia (dogs, bears, raccoons, mustelids and pinnipeds; see Flynn and Nedbal, 1998;Bininda-Emonds et al, 1999). Recently, karyotypic relationships between and within major carnivore families (Felidae, Ursidae, Canidae, Mustelidae) have been revisited by cross-species chromosome painting (Nash et al, 1998(Nash et al, , 2001Yang et al, 2000;Graphodatsky et al, 2001Graphodatsky et al, , 2002Nie et al, 2002;Tian et al, 2002Tian et al, , 2004Yang and Graphodatsky, 2004), leading to the formulation of putative ancestral karyotypes for these major families and for the order Carnivora. The karyotypic evolution within the Caniformia is relatively well resolved, but karyotypic relationships among representative species in the suborder Feliformia, remain to be defined.…”

“…While the paint probes from karyotypically conserved species such as the domestic cat and human are informative in revealing the interchromosomal rearrangements, painting probes from the highly rearranged dog genome have proved to be highly informative in detecting cryptic intrachromosomal rearrangements in the American mink (Graphodatsky et al, 2000b), domestic cat , African lion, clouded leopard, Malayan sun bear (Tian et al, 2004) as well as in human (Yang et al, 1999;Yang and Graphodatsky et al, 2004) and pig (Biltueva et al, in press). The present investigation is no exception.…”

“…Further comparison with species outside the Feliformia suborder, such as the Malayan sun bear (Tian et al, 2004), spectacled bear (Yang and Graphodatsky, 2004), human (Yang et al, 1999), pig (Biltueva et al, in press), particularly the rabbit and aardvark (Yang, unpublished data), the latter having relatively more conserved karyotypes than the human and the pig, enables us to deduct the polarity of the chromosome rearrangements that differentiate extant Feliformia karyotypes. For instance, the equivalent chromosomes of ACK1q ( = FCA C2) in the hyena, civet and domestic cat display different painting patterns: CFA 27/30/35/23 in the civet and cat, but CFA 27/ 30/23/35 in the hyena.…”

“…Therefore, it is most likely that the CFA 27/30/35/23 arrangement seen in the civet and cat chromosomes represents the ancestral state for ACK1q while the inverted pattern found in the hyena is the derived state. Moreover, ACK1 ( = FCA A2p+C2 = HSA 19p+3/21 = CFA 20a+27/ 30/35/23) has been retained in the mustelids (Hameister et al, 1997;Graphodatsky et al, 2000b;Nie et al, 2002), pinniped (Frönicke et al, 1997) and red panda Tian et al, 2002), but is represented by two syntenic blocks (ACK1q = CFA 27/30/35/23 and ACK1p = CFA 20a) in all the Feliformia and three blocks (CFA 27/30/35a, CFA 35b/23 and CFA 20a) in the ursid species (Nash et al, 2001;Tian et al, 2004). The ACK1 has broken into three syntenic blocks in human (HSA 3,19p and 21).…”

Canine cytogenetics – from band to basepair

“…For example, cytogenetic resources developed for the dog have also played a role in extending comparative cytogenetics beyond the Canidae by expanding cross-species painting studies to include members of the Felidae and Ursidae, both of which also belong to the order Carnivora (Tian et al, 2004).…”