Cytogenetic Mapping of Cattle BAC Probes for the Hypothetical Ancestral Karyotype of the Family Cervidae

Abstract

Cervids are characterized by their greatest karyotypic diversity among mammals. A great diversity of chromosome numbers in notably similar morphological groups leads to the existence of several complexes of cryptic species and taxonomic uncertainties. Some deer lineages, such as those of Neotropical deer, stand out for a rapid chromosomal reorganization and intraspecific chromosome polymorphisms, which have not been properly explored yet. For that reason, we contribute to the study of deer karyotype diversity and taxonomy by producing and characterizing new molecular cytogenetic markers for the gray brocket deer (<i>Subulo gouazoubira</i>), a deer species that retained the hypothetical ancestral karyotype of Cervidae. We used bacterial artificial chromosome (BAC) clones derived from the cattle genome (<i>Bos taurus</i>) as markers, which were hybridized on <i>S. gouazoubira</i> metaphase chromosomes. In total, we mapped 108 markers, encompassing all gray brocket deer chromosomes, except the Y chromosome. The detailed analysis of fluorescent in situ hybridization results showed 6 fissions and 1 fusion as interchromosomal rearrangements that have separated cattle and gray brocket deer karyotypes. Each group of BAC probes derived from bovine chromosome pairs 1, 2, 5, 6, 8, and 9 showed hybridization signals on 2 different chromosomes, while pairs 28 and 26 are fused in tandem in a single acrocentric chromosome in <i>S. gouazoubira</i>. Furthermore, the BAC markers detected the occurrence of intrachromosomal rearrangements in the <i>S. gouazoubira</i> chromosomes homologous to pair 1 and the X chromosome of cattle. We present a karyotypic map of the 108 new markers, which will be of great importance for future karyotypic evolution studies in cervids and, consequently, help in their conservation and taxonomy resolution.

Comparative studies of X chromosomes in Cervidae family

“…In Cervidae family, an elevated level of morphological variation of the X chromosome was revealed using GTG staining 19 and confirmed by BAC-clone hybridization in several cervid species 20 , 22 , 24 . To investigate the order of conserved syntenic segments on X chromosomes in the Cervidae family, 29 bovine BAC-clones were localized using FISH (fluorescence in situ hybridization) on X chromosomes of seven species from both subfamilies: black muntjak, tufted deer, sika deer, red deer, reindeer, Chinese water deer, and gray brocket deer in a series of pairwise FISH experiments.…”

“…The analysis of the corrected order with other research 22 and new data shows that, milu deer X chromosome represents the typical acrocentric type of cervid X. We also compared BACs’ order from previous research 24 of gray brocket deer X chromosome with new data. The variation of the acrocentric type of X is conditioned by autosomal translocation and heterochromatin expansion.…”

“…Artiodactyl sex chromosomes, especially the X, demonstrate high levels of evolutionary rearrangements, including inversions, centromere shift, heterochromatic variation, and X-autosomal translocations 19 . Recently, a series of investigations of X chromosome evolution in different artiodactyl species, including several Cervidae species, were published employing high-resolution BAC mapping 15 , 20 , 22 , 24 . Combining new data with previously obtained data 15 , 20 , 22 , 24 is possible to trace the path of transformation of the X chromosome in various branches of the Cervidae family.…”

“…X-chromosomal changes in Ruminantia include inversions, centromere shifts, heterochromatic variation, and X-autosomal translocations. Recently the X chromosome evolution in different representatives of artiodactyl species was studied by high-resolution BAC (Bacterial Artificial Chromosomes) mapping 15 , 20 , 22 – 24 . Cervidae X chromosomes were investigated previously by band-specific probes 25 , BACs 15 , 20 , 22 , 24 , and oligo 26 probe localization.…”

“…Recently the X chromosome evolution in different representatives of artiodactyl species was studied by high-resolution BAC (Bacterial Artificial Chromosomes) mapping 15 , 20 , 22 – 24 . Cervidae X chromosomes were investigated previously by band-specific probes 25 , BACs 15 , 20 , 22 , 24 , and oligo 26 probe localization. A substantial part of the cervid X chromosome can be formed by heterochromatin which can be interspersed or present in blocks in the intercalary or pericentromeric regions.…”