Chromosomal Aberrations As a Biological Phenomenon in Human Embryonic Development

Abstract

Frequent chromosomal abnormalities are a distinctive feature of early embryonic development in mammals, especially humans. Aneuploidy is considered as a contributing factor to failed embryo implantation and spontaneous abortions. In the case of chromosomal mosaicism, its effect on the potency of embryos to normally develop has not been sufficiently studied. Although, a significant percentage of chromosomal defects in early human embryos are currently believed to be associated with the features of clinical and laboratory protocols, in this review, we focus on the biological mechanisms associated with chromosomal abnormalities. In particular, we address the main events in oocyte meiosis that affects not only the genetic status of an unfertilized oocyte, but also further embryo viability, and analyze the features of first cleavage divisions and the causes of frequent chromosomal errors in early embryonic development. In addition, we discuss current data on self-correction of the chromosomal status in early embryos.

Keywords: aneuploidy; chromosomal mosaicism; preimplantation development.

Fig. 1

Efficiency of IVF cycles, depending on the chromosomal status of gametes and embryos. Euploid cells are indicated in green, aneuploid cells are indicated in pink. 1) According to literature data, human spermatozoa in the vast majority of cases do not carry chromosomal abnormalities [23, 24]. 2) Mean rate of chromosomal abnormalities in human oocytes. The proportion of aneuploid oocytes varies from 20% to 80–90%, depending on maternal age (see [80]). 3) Mean rate of embryo mosaicism, based on experimental data [10, 15, 16]. 4) Blastocyst rate in embryos with different chromosomal statuses, according to experimental data [81]. 5) Clinical outcomes after transfer of euploid and mosaic embryos, according to experimental data [19]

Fig. 2

Models of self-correction of the chromosomal status in mosaic embryos. Euploid cells are indicated in green, aneuploid cells are indicated in pink. Spindles (1.1) reflect an increase in the proliferative activity of euploid cell lines in mosaic embryos. Black crosses indicate apoptotic processes in aneuploid cells (1.2). A trisomal aneuploid embryonic cell (2.1) can undergo corrective mitotic division. One of the chromosomes remains at the mitotic spindle equator due to merotelic attachment of microtubules to kinetochores (2.2) and is not further included in the nuclei of daughter cells (2.3). (3.1, 3.2) Displacement of aneuploid cells to the embryo periphery, to the area of the nascent trophectoderm