Chromosome Abnormalities in the Human Oocyte

Abstract

Aneuploidy is the most commonly occurring type of chromosome abnormality and the most significant clinically. It arises mostly due to segregation errors taking place during female meiosis and is also closely associated with advancing maternal age. Two main aneuploidy-causing mechanisms have been described: the first involves the non-disjunction of entire chromosomes and can take place during both meiotic divisions, whereas the second involves the premature division of a chromosome into its 2 sister chromatids, followed by their random segregation, upon completion of meiosis I. To elucidate the causal mechanisms of maternally derived aneuploidy and the manner with which they affect the 2 meiotic divisions, a large number of oocytes and their corresponding polar bodies have been examined. Various classical and molecular cytogenetic methods have been employed for this purpose, and valuable data have been obtained. Moreover, research into the gene expression patterns of oocytes according to maturity, maternal age, and chromosome status has provided a unique insight into the complex nature of the biological processes and genetic pathways regulating female meiosis. Findings obtained from the cytogenetic and molecular analysis of oocytes will be reviewed in this article.

Meiotic non-disjunction mechanisms in human fertile males

“…Meiotic non-disjunction in humans: few differences between male and female As observed in the current work and in human female meiosis (reviewed by Pellestor et al, 2006;Jones, 2008;Fragouli et al, 2011), spermatogenesis and oogenesis show resemblances with regard to meiosis I non-disjunction events, such as the similar contribution of PSSC and achiasmate non-disjunction to the genesis of aneuploidy and the predominant involvement of chromosomes of smaller size.…”

Insights into Mechanisms Causing the Maternal Age-Induced Decrease in Oocyte Quality

“…Additionally, faithful segregation of chromosomes at MI did not guarantee MII segregation would occur without error. One of the most frequently involved chromosomes in aneuploidy was chromosome 21 [ 60 ]. Corroborating evidence from mouse models for advanced maternal age shows aneuploidy rates due to nondisjunction at MI increased signifi cantly at 12 months of age and are even higher in 15 months.…”

Maternal age and in vitro culture affect mitochondrial number and function in equine oocytes and embryos

“…One of the proposed underlying predispositions to aneuploidy and compromised developmental competence of oocytes and embryos from older women is mitochondrial dysfunction. Compromised mitochondrial function appears to stem from defective mitochondrial replication (leading to a fall in mitochondrial numbers), an increase in the incidence of mitochondrial (mt) DNA aberrations, such as point mutations and deletions, and increased production and release of reactive oxygen species (ROS); Takeuchi et al 2005;Carnevale 2008;Fragouli et al 2011). The number of mitochondria in an oocyte can be estimated by analysis of mtDNA copy number because oocytes contain only one to two mtDNA copies per mitochondrion (Pikó and Matsumoto 1976;Pikó and Taylor 1987;Jansen 2000;Santos et al 2006b;Jiao et al 2007;Chiaratti and Meirelles 2010).…”