Increased Expression of Maturation Promoting Factor Components Speeds Up Meiosis in Oocytes from Aged Females

Abstract

The rate of chromosome segregation errors that emerge during meiosis I in the mammalian female germ line are known to increase with maternal age; however, little is known about the underlying molecular mechanism. The objective of this study was to analyze meiotic progression of mouse oocytes in relation to maternal age. Using the mouse as a model system, we analyzed the timing of nuclear envelope breakdown and the morphology of the nuclear lamina of oocytes obtained from young (2 months old) and aged females (12 months old). Oocytes obtained from older females display a significantly faster progression through meiosis I compared to the ones obtained from younger females. Furthermore, in oocytes from aged females, lamin A/C structures exhibit rapid phosphorylation and dissociation. Additionally, we also found an increased abundance of MPF components and increased translation of factors controlling translational activity in the oocytes of aged females. In conclusion, the elevated MPF activity observed in aged female oocytes affects precocious meiotic processes that can multifactorially contribute to chromosomal errors in meiosis I.

Expression of lamin C2 in mammalian oocytes

“…The nuclear envelope plays a critical role in the regulation of many cellular events as well as maintaining genomic stability and regulating protein/RNA transport in and out of the nucleus [28,29]. Previously we reported that the expression of both LMN A and C does not change in oocytes with increased female age [20]. Surprisingly we found that the LMN C2 protein is significantly decreased in the oocytes of aged females in comparison to young females.…”

“…However, we detected Lmnc2 mRNA in the testicular and juvenile ovarian samples, but not in the fully grown GV oocytes ( Fig 4A). Next we validated our RT-PCR results by treating fully grown GV oocytes with the translational repressor cycloheximide PLOS ONE (CHX) [18][19][20][21][22]. LMN C2 protein levels were unaffected by inhibition of translation ( Fig 4B and 4C), indicating stability of the LMN C2 protein at this oocyte development stage and independence of LMN C2 protein level on new translation.…”

“…We detected the expression of all LMN A/C forms in the mouse oocytes ( Figs 1A and 3). Recently we reported that both LMN A and LMN C are expressed equally during meiotic progression in adult females, in particular between young (2 months old) and aged (12 months old) female groups [20]. Based on this, we analysed the expression of LMN C2 in the oocytes isolated from young and aged females during meiotic maturation from the GV to the MII stage.…”

“…Despite this and given that in oocytes LMN C2 is still present at the nuclear envelope after synaptic pairing, it would be conceivable that during oogenesis the LMN C2 protein may have a second, subsequent function in later oocyte stages. Several studies demonstrated that during aging cells undergo age-related changes in nuclear architecture [20,[23][24][25]. Accordingly, decreasing concentrations or the complete loss of LMN C2 protein may possibly lead to increased chromosomal segregation errors in oocytes from aged females.…”

Wwc2 Is a Novel Cell Division Regulator During Preimplantation Mouse Embryo Lineage Formation and Oogenesis

“…Exploiting alternative, oligo-dT versus random hexamer, cDNA synthesis priming strategies we uncovered evidence of cytoplasmic Wwc2 mRNA poly-adenylation, usually associated with increased translational efficiency of functionally important proteins during meiotic maturation (Salles et al, 1992) - Figure 3A. Consultation of our previously published assay of polysome associated transcripts during mid-meiotic maturation supported this interpretation, reporting ∼40% polysome association of detectable Wwc2 transcripts (Koncicka et al, 2018;Masek et al, 2020). We then confirmed by Q-RT-PCR that our siRNA construct could elicit robust Wwc2 transcript knockdown in microinjected GV oocytes blocked from re-entering meiosis I (using the cAMP/cGMP phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine/ IMBX) but then permitted to in vitro mature (IVM -via IBMX removal) to the MII equivalent stage (Figures 3B,C).…”