Pre- and Postovulatory Aging of Murine Oocytes Affect the Transcript Level and Poly(A) Tail Length of Maternal Effect Genes

Abstract

Maternal effect genes code for oocyte proteins that are important for early embryogenesis. Transcription in oocytes does not take place from the onset of meiotic progression until zygotic genome activation. During this period, protein levels are regulated posttranscriptionally, for example by poly(A) tail length. Posttranscriptional regulation may be impaired in preovulatory and postovulatory aged oocytes, caused by delayed ovulation or delayed fertilization, respectively, and may lead to developmental defects. We investigated transcript levels and poly(A) tail length of ten maternal effect genes in in vivo- and in vitro- (follicle culture) grown oocytes after pre- and postovulatory aging. Quantitative RT-PCR was performed using random hexamer-primed cDNA to determine total transcript levels and oligo(dT)16-primed cDNA to analyze poly(A) tail length. Transcript levels of in vivo preovulatory-aged oocytes remained stable except for decreases in Brg1 and Tet3. Most genes investigated showed a tendency towards increased poly(A) content. Polyadenylation of in vitro preovulatory-aged oocytes was also increased, along with transcript level declines of Trim28, Nlrp2, Nlrp14 and Zar1. In contrast to preovulatory aging, postovulatory aging of in vivo- and in vitro-grown oocytes led to a shortening of poly(A) tails. Postovulatory aging of in vivo-grown oocytes resulted in deadenylation of Nlrp5 after 12 h, and deadenylation of 4 further genes (Tet3, Trim28, Dnmt1, Oct4) after 24 h. Similarly, transcripts of in vitro-grown oocytes were deadenylated after 12 h of postovulatory aging (Tet3, Trim28, Zfp57, Dnmt1, Nlrp5, Zar1). This impact of aging on poly(A) tail length may affect the timed translation of maternal effect gene transcripts and thereby contribute to developmental defects.

The subcortical maternal complex: multiple functions for one biological structure?

“…Aberrant expression of SCMC members was observed in different animal models of differential competence [19,64,65], while MATER abundance was repeatedly associated with maternal ageing in mice [66][67][68][69][70] suggesting that a decrease or absence of NLRP5 may result in compromised fertility in women of advanced reproductive age. Moreover, NLRP5 altered expression in abnormal human embryos and developmentally arrested two-cell embryos strongly suggests a role in preimplantation embryo development [71,72].…”

Effect of Type I Diabetes on the Proteome of Mouse Oocytes

“…Cumulus oocyte complexes (COCs) were isolated from diabetic and control mice 14 h after hCG injection. COCs were treated with 1 mg/mL hyaluronidase, and metaphase II (MII)-stage oocytes were isolated, We showed the above protocol by visual representation [10] (Fig. 1).…”

Preovulatory oocyte aging in mice affects fertilization rate and embryonic genome activation

“…The molecular causes behind the decreased oocyte competence of preovulatory-aged oocytes are still unclear. In a previous study we showed that preovulatory aging affects the expression levels and poly(A)-tail length of maternal effect genes (Dankert et al 2014). This group of genes is expressed in the oocyte but regulates processes in the early embryo such as zygotic genome activation (ZGA) and the maintenance of DNA methylation of imprinted genes.…”

“…The first major step occurs around the 2-cell stage and is crucial for further embryonic development (Schultz 1993;Hamatani et al 2004;Wang et al 2004). In the preovulatory-aged oocyte, relative mRNA expression of Smarca4, Tet3 and Zfp57 is decreased (Dankert et al 2014). Smarca4 encodes the catalytic subunit of SWI/SNF-related complexes and regulates chromatin remodeling in the process of ZGA (Bultman et al 2006).…”

“…To analyze whether the deregulation of maternal effect genes observed after preovulatory aging (Dankert et al 2014) affects the developmental potential of the oocyte, the current study investigated the developmental competence of preovulatory-aged oocytes. Fertilization rates as well as the capacity to activate the embryonic genome at the 2-cell stage were found to be affected by preovulatory aging.…”