Karyotype relationships among selected deer species and cattle revealed by bovine FISH probes

Abstract

The Cervidae family comprises more than fifty species divided into three subfamilies: Capreolinae, Cervinae and Hydropotinae. A characteristic attribute for the species included in this family is the great karyotype diversity, with the chromosomal numbers ranging from 2n = 6 observed in female Muntiacus muntjak vaginalis to 2n = 70 found in Mazama gouazoubira as a result of numerous Robertsonian and tandem fusions. This work reports chromosomal homologies between cattle (Bos taurus, 2n = 60) and nine cervid species using a combination of whole chromosome and region-specific paints and BAC clones derived from cattle. We show that despite the great diversity of karyotypes in the studied species, the number of conserved chromosomal segments detected by 29 cattle whole chromosome painting probes was 35 for all Cervidae samples. The detailed analysis of the X chromosomes revealed two different morphological types within Cervidae. The first one, present in the Capreolinae is a sub/metacentric X with the structure more similar to the bovine X. The second type found in Cervini and Muntiacini is an acrocentric X which shows rearrangements in the proximal part that have not yet been identified within Ruminantia. Moreover, we characterised four repetitive sequences organized in heterochromatic blocks on sex chromosomes of the reindeer (Rangifer tarandus). We show that these repeats gave no hybridization signals to the chromosomes of the closely related moose (Alces alces) and are therefore specific to the reindeer.

Fig 1. A dendrogram representing phylogenetic relationships between the studied Cervidae species and other Pecoran members.

The numbers correspond to the bovine chromosome equivalents. The distances between species are not representative of the evolution time.

Fig 2. G-banded karyotype of the rusa deer (Cervus timorensis russa) with chromosome homologies to the cattle (Bos taurus, BTA).

Lines on the sides of CTR1-6 chromosome indicate boundaries between two cattle probes.

Fig 3. FISH examples demonstrating evolutionary rearrangements between cattle and various Cervidae species.

(A) Tandem fusion of BTA28/26 in milu deer (EDA) detected by region specific painting probes BTA26dist (red) and BTA28dist (green) (B) Centric fusion of BTA17 (red) and 19 (green) in rusa deer (CTR). (C) Centric fusion of BTA29/17 in moose (AAL) validated by probes BTA29dist (green) and BTA17dist (red). (D) Hybridization of BTA1 on reindeer (RTA) submetacentric and acrocentric orthologs. Centromeres are marked by lines.

Fig 4. Rearrangements on Chinese muntjac chromosomes MRE1–5 and 11 are demonstrated by hybridization patterns of appropriate cattle painting probes (on the right).

Fig 5. FISH showing hybridization of BTA1 BAC probes and their schematic illustration in various Cetartiodactyl species.

(A) Hybridization of cattle probes BAC1qp (pink), BAC1qd (green), and BAC1qt (red) probes on chromosomes of cattle (BTA), rusa deer (CTR) and reindeer (RTA). (B) Schematic illustration demonstrating rearrangements of BTA1 orthologs in rusa deer (CTR), Chinese muntjac (MRE), reindeer (RTA), pronghorn (AAM), giraffe (GCA), okapi (OJO) and pygmy hippo (CLI). The dots approximate the positions of BAC1qp (pink), BAC1qd (green), and BAC1qt (red) probes.

Fig 6. Schematic illustration showing X chromosome segments in cattle (BTA) and their counterparts in roe deer (CCA), milu deer (EDA) and giraffe (GCA).

The cattle BAC probes were divided into four groups marked with different colours. Positions of the BAC clones are on the side of the chromosome.

Fig 7. Hybridization results of heterochromatin specific clones on reindeer (RTA) chromosomes.

(X, Y—gonosomes; A-autosome).