Hartmann's Zebra Research Articles

Subchromosomal karyotype evolution in Equidae

Equidae is a small family which comprises horses, African and Asiatic asses, and zebras. Despite equids having diverged quite recently, their karyotypes underwent rapid evolution which resulted in extensive differences among chromosome complements in respective species. Comparative mapping using whole-chromosome painting probes delineated genome-wide chromosome homologies among extant equids, enabling us to trace chromosome rearrangements that occurred during evolution. In the present study, we performed subchromosomal comparative mapping among seven Equidae species, representing the whole family. Region-specific painting and bacterial artificial chromosome probes were used to determine the orientation of evolutionarily conserved segments with respect to centromere positions. This allowed assessment of the configuration of all fusions occurring during the evolution of Equidae, as well as revealing discrepancies in centromere location caused by centromere repositioning or inversions. Our results indicate that the prevailing type of fusion in Equidae is centric fusion. Tandem fusions of the type telomere-telomere occur almost exclusively in the karyotype of Hartmann's zebra and are characteristic of this species' evolution. We revealed inversions in segments homologous to horse chromosomes 3p/10p and 13 in zebras and confirmed inversions in segments 4/31 in African ass, 7 in horse and 8p/20 in zebras. Furthermore, our mapping results suggested that centromere repositioning events occurred in segments homologous to horse chromosomes 7, 8q, 10p and 19 in the African ass and an element homologous to horse chromosome 16 in Asiatic asses. Centromere repositioning in chromosome 1 resulted in three different chromosome types occurring in extant species. Heterozygosity of the centromere position of this chromosome was observed in the kiang. Other subtle changes in centromere position were described in several evolutionary conserved chromosomal segments, suggesting that tiny centromere repositioning or pericentric inversions are quite frequent in zebras and asses.

Interstitial telomeric sites and NORs in Hartmann's zebra (Equus zebra hartmannae) chromosomes.

Interstitial telomeric sites (ITSs) are considered as signatures of chromosomal rearrangements that take place during karyotype evolution. Understanding that equids have undergone rapid karyotype evolution compared with the average in other mammals, a search of these signatures was carried out in the Hartmann's mountain zebra (Equus zebra hartmannae; EZH) chromosomes. Six consistent ITSs were identified on five of the zebra chromosomes (EZH1p, 1q, 2q, 5q, 6q and 11q). The location of these ITSs coincided with fusion points of some of the evolutionarily conserved human-Hartmann's zebra chromosomal segments suggesting that the sequences are remnants of fusion events between ancestral chromosomes. Incidentally, three of the ITSs also matched with the presence of constitutive heterochromatin. Further, ribosomal gene clusters were localized on five zebra chromosomes and the data were compared with those in other equid species. The findings offer preliminary evidence on the likely evolution of some of the Hartmann's zebra chromosomes and add to the current search for clues that lead to the ancestral chromosomal configuration in equids.

A comparison of the mineral composition of milk of domestic and captive wild equids ( Equus Przewalski, E. Zebra, E. Burchelli, E. Caballus, E. Assinus)

1. 1. Milk samples were obtained in early and/or late lactation from Przewalski horses, Hartmann's zebras, Grant's zebras, domestic horses, ponies and a mule mare made pregnant by embryo transfer. 2. 2. Samples were compared for their content of total solids, ash, calcium, phosphorus, magnesium, sodium, potassium, copper, zinc and iron. 3. 3. Milk from the Przewalski horses, Hartmann's zebra and the domestic horse had similar mineral composition and the content of minerals was higher in early than in late lactation. 4. 4. Milk from the domestic mule contained the lowest concentration of calcium, phosphorus and zinc but the highest concentration of magnesium, sodium and potassium. 5. 5. Milk from the Grant's zebras contained more sodium than potassium, unlike milk from Przewalski horses, Hartmann's zebras or domestic horses in which there was more potassium than sodium.

Structural Comparison of the Hemoglobins of the Genus Equus with Those of Ruminants

Abstract The hemoglobin structures from domestic horse, tarpan horse, and przewalski's horse, donkey, and four subspecies of zebra are compared by peptide mapping and specific staining, with limited isolation of peptides followed by amino acid analysis. Peptide mapping techniques are used to indicate the between phenylalanine and tyrosine at amino acid position α-24 in domestic horse. Such ambiguity at this position cannot be found in the α chain of 51 donkey hemoglobin samples, and is not evident in other equine species. Comparison of the hemoglobin polypeptide chains of the equine family reveals striking similarity among the β chains and a limited number of differences among the α chains. The number of amino acid interchanges accounting for species differences in the α chain are small in contrast to the numerous differences occurring in the α chains of the ruminants. Serine is present at position α-15 in the horse, donkey, and Hartmann's zebra hemoglobins, whereas glycine is present at α-15 in all the other zebra subspecies studied. The limited structural differences in the equine genus are contrasted to the recently reported variations which account for the polymorphic hemoglobins of ruminants. The genetic control of the hemoglobins of the horse, based upon three pairs of alleles for the two different α and single β chains is proposed and compared to a nonallelic scheme for sheep hemoglobins. The numerous evolutionarily effective amino acid substitutions seen in ruminant hemoglobins as compared to other species are accentuated by this comparison within the genus Equus.