Screening of in vitro-produced cattle embryos to assess incidence and characteristics of unbalanced chromosomal aberrations

Abstract

Graphical Abstract Summary: Pregnancy rates of in vitro-produced cattle embryos are lower than those of in vivo-produced embryos. One of the reasons may be the increase in chromosomal aberrations due to in vitro maturation and fertilization of the oocyte. Currently, embryo transfer is commonly applied in nucleus cattle breeding programs, and the embryos are genotyped for genomic selection. Therefore, intensity data from SNP arrays can be exploited for preimplantation genetic testing by screening the intensity data of the embryos for unbalanced chromosomal aberrations. A total of 558 stage 8 Dutch Holstein embryos genotyped with SNP arrays were screened in an observational study in retrospect. We found 22 affected embryos, showing either aneuploidy or ploidy issues; monosomy was most frequently observed. Given that embryo genotypes are readily available, preimplantation genetic screening can easily be applied to gain more insight in the characteristics of unbalanced chromosomal aberrations and their pregnancy outcomes.

Embryo biopsies for genomic selection in tropical dairy cattle

“…Recently, PGT-A human-like approaches have been applied to bovine embryos, such as the use of Karyomapping (a SNP-based screening test that allows detection of aneuploidy) ( Griffin et al, 2019 ). Using SNP-based assays, 5% ( Bouwman and Mullaart, 2023 ) to 14.1% ( Silvestri et al, 2021 ) of chromosomal abnormalities, involving aneuploid and ploidy issues, were described. Aneuploid bovine embryos have only 5.8% chance of establishing a pregnancy after their transfer, compared to 59.6% chance of euploid embryos ( Silvestri et al, 2021 ).…”

Developmental Hurdles That Can Compromise Pregnancy during the First Month of Gestation in Cattle

“…Chromosomal anomalies may also occur during mitosis, and this can produce aneuploidy when it occurs at the one-cell stage, or a mosaicism referred to as mixoploidy if it occurs on or after the two-cell stage. Aneuploidy and mixoploidy incidences range from 5% to 25% in IVP bovine embryos [102][103][104]. Only ~5% of these embryos will reach the blastocysts stage [102,103], and pregnancy rates from these embryos are very low (<5%) [102,103].…”

“…Aneuploidy and mixoploidy incidences range from 5% to 25% in IVP bovine embryos [102][103][104]. Only ~5% of these embryos will reach the blastocysts stage [102,103], and pregnancy rates from these embryos are very low (<5%) [102,103]. This outcome is not surprising given the lethal nature of these chromosomal abnormalities.…”

“…Thus, limiting the incidence of aneuploidy and mixoploidy and/or screening for these anomalies before ET can be an effective way to improve pregnancy success when using IVP embryos. Embryo screening may not be too far from being realized in cattle if the current trend of genomic testing in IVP bovine embryos continues [102][103][104].…”

Pre-Implantation Bovine Embryo Evaluation—From Optics to Omics and Beyond

“…Genomic studies using SNP genotyping have been carried out in pre-implantation bovine embryos mainly to test for aneuploidy [ 132 , 135 , 136 , 137 ], chromosomal aberrations [ 136 , 138 ], and karyomapping [ 135 , 139 ] to date. After identifying euploid embryos for transfer (from karyomapped IVP embryos), live calves were born, demonstrating that genomic/SNP studies indeed have ground-level applications [ 135 ].…”