Aneuploidy Detection in Pigs Using Comparative Genomic Hybridization: From the Oocytes to Blastocysts

Data on the frequency of aneuploidy in farm animals are lacking and there is the need for a reliable technique which is capable of detecting all chromosomes simultaneously in a single cell. With the employment of comparative genomic hybridization coupled with the whole genome amplification technique, this study brings new information regarding the aneuploidy of individual chromosomes in pigs. Focus is directed on in vivo porcine blastocysts and late morulas, 4.7% of which were found to carry chromosomal abnormality. Further, ploidy abnormalities were examined using FISH in a sample of porcine embryos. True polyploidy was relatively rare (1.6%), whilst mixoploidy was presented in 46.8% of embryos, however it was restricted to only a small number of cells per embryo. The combined data indicates that aneuploidy is not a prevalent cause of embryo mortality in pigs

Published frequency of aneuploidy in pigs.

a<p>only chromosomes 1, 10 and Y detected.</p>b<p>only chromosomes 1 and 10 detected.</p>c<p>only hyperhaploidy.</p>d<p>only true polyploidy without mixoploidy.</p>e<p>polyploidy+mixoploidy.</p

The incidence and description of aneuploidies in pig embryos detected by CGH.

a<p>aneuploid embryo was at the late morula stage.</p><p>The table summarizes the numbers of embryos collected and analyzed from individual gilts. Besides that, data on the sex ratio, numbers of abnormal embryos and the description of chromosome abnormalities are provided.</p

The incidence and description of ploidy abnormalities in pig embryos detected by FISH.

a<p>embryo contained 98% of triploid cells, therefore it is considered as triploid.</p><p>The frequencies of ploidy abnormalities are grouped with respect to the percentage of abnormal cells within individual embryos (first column). On the right side of the table, the numbers and description of ploidy mosaicism is given; for example, in the group of embryos with ploidy abnormalities 0–5%, 11 embryos contained beside diploid cells only tetraploid cells etc.</p

The occurrence of individual pig chromosomes in aneuploid oocytes, early embryos and blastocysts.

a<p>the results of the CGH analysis of oocytes were published in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030335#pone.0030335-Hornak1" target="_blank">[7]</a>.</p>b<p>the results of the CGH analysis of early embryos were published in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030335#pone.0030335-Hornak2" target="_blank">[8]</a>.</p>c<p>present study.</p><p>The table shows individual pig chromosomes and their occurrence in aneuploid samples. The aneuploid samples containing >3 chromosome abnormalities per oocyte/embryo (complex aneuploidy with a likely stochastic distribution of chromosome errors) and samples containing segmental chromosome abnormalities were excluded.</p

The example of WGA-CGH analysis of 2 aneuploid pig embryos.

<p>(A) the male embryo detected with partial loss of chromosome 9q; (B) the female embryo detected with loss of chromosomes 13 and 14. Amplified DNA obtained from the embryo was labelled with red fluorescence and amplified reference male porcine DNA was labeled with green fluorescence. Both DNA samples were mixed and allowed to hybridize to male porcine mitoses. Subsequently, the red and green fluorescence was captured and analyzed using dedicated CGH software. The heterochromatin regions (e.g. centromeres and the q arm of chromosome Y) were excluded from the analysis due to the abundance of repetitive DNA sequences.</p