Whole-comparative genomic hybridization in domestic sheep <i>(Ovis aries)</i> breeds

Abstract

Whole-comparative genomic hybridization (W-CGH) allows identification of chromosomal polymorphisms related to highly repetitive DNA sequences localized in constitutive heterochromatin. Such polymorphisms are detected establishing competition between genomic DNAs in an in situ hybridization environment without subtraction of highly repetitive DNA sequences, when comparing two species from closely related taxa (same species, sub-species, or breeds) or somewhat related taxa. This experimental approach was applied to investigating differences in highly repetitive sequences of three sheep breeds (Castellana, Ojalada, and Assaf). To this end, W-CGH was carried out using mouflon (sheep ancestor) chromosomes as a common target to co-hybridize equimolar quantities of two genomic DNAs obtained from either Castellana, Ojalada or Assaf sheep breeds. The results showed that the amount of constitutive heterochromatin is greater in all pericentromeric heterochromatin regions of acrocentric chromosomes than in metacentric or sex chromosomes. Additionally, when W-CGH was performed using DNAs from the Iberian breeds Castellana and Ojalada, chromosomal pericentromeric regions revealed quantitatively and qualitatively a presence of DNA families similar to that obtained from any of the above-cited breeds. On the contrary, when the DNA used in W-CGH experiments was obtained from Assaf, as compared to either Castellana or Ojalada, two different pericentromeric DNA families of highly repetitive sequences could be detected. Lastly, sex chromosomes were shown to be homogeneous among all breeds and thus revealed no detectable constitutive heterochromatin. W-CGH results were confirmed using DNA breakage detection-FISH experiments (DBD-FISH) carried out on lymphocytes. As a whole, the results showed that two different repetitive DNA families are present in the pericentromeric heterochromatin of the sheep breeds studied here. Additionally, they suggest a differential presence of these distinct repetitive DNA families in Castellana and Ojalada breeds as compared to the Assaf breed. Finally, the results of W-CGH after using mouflon as the targeted chromosomes also show that the two DNA families are present in the ancestor.

Evolution of satellite DNA sequences in two tribes of Bovidae: A cautionary tale

“…Our results agree with data produced by Chaves et al . (2000) and by Davila-Rodriguez et al . (2009) , who found that the amount of constitutive heterochromatin is greater in all pericentromeric regions of acrocentric chromosomes than in metacentric or sex chromosomes.…”

Digital Agenesia in Martina Franca Donkey Foal: A Case Report

“…Polymorphisms due to the accretion of duplicated genomic segments are common in mammalian genomes, in particular at centromeric and telomeric regions where they are usually silenced and show no effect on the phenotype [12][13][14][15]. In mammalian species, unexplored polymorphisms were identified in swine, sheep, stallions, and donkeys [16][17][18], and the technique also provided evidence for the presence of highly conserved repetitive DNA.…”

Molecular Cytogenetics and Gene Mapping in Sheep (<i>Ovis aries, </i>2n = 54)

“…Procedures for the identification of chromosomal polymorphisms such as whole-comparative genomic hybridization (W-CGH) or DNA breakage detection FISH (DBD-FISH) have also proven useful in phylogenetic studies between domestic sheep and the mouflon, a direct ancestor [Dávila-Rodríguez et al, 2009]. Expanding such studies to other Ovis species should improve information about the genetic diversity and evolution of the genus Ovis and complement other phylogenetics studies such as the recent study that used retroviral insertion to delineate different sheep lineages and mitochondrial lineages studies [e.g.…”