The study of mammalian oocyte competence by transcriptome analysis: progress and challenges

Abstract

Various morphological and cytological traits of oocytes and their surrounding cumulus cells may be used to select oocytes for assisted reproduction. However, even with careful selection, successful IVF and subsequent embryo development remain uncertain. The factors that ensure oocyte competence are unclear and other approaches to assessing developmental potential must be explored. With the constant development of the molecular toolbox, genomic/transcriptomic analysis is becoming a more and more interesting approach to understand oocyte quality on the basis of RNA composition. Using bovine and mouse models as well as human oocytes of known developmental potential, various efforts are underway to characterize the mRNA profile of the competent oocyte using microarray technology. The proliferation of gene expression data sets raises new opportunities to identify the mechanisms involved in this complex phenotype, which should lead to improved techniques of assisted reproduction. Although several molecular markers of oocyte quality are known, translating these into cellular functions remains challenging, largely due to the poor correlation between mRNA level and protein synthesis. Unlike most somatic cells, the oocyte can store mRNA for days, with transcriptional activity remaining at a halt during the 4-5 days beginning before ovulation and ending with embryonic genome activation. This review provides an overview of the transcriptomic data obtained from oocytes of different quality as well as interesting avenues to explore in order to improve our understanding of oocyte competence.

Identification of Maturation-Specific Proteins by Single-Cell Proteomics of Human Oocytes

“…Therefore, we selected several data sets from the literature that have exhaustively characterized the proteomes of cell types distantly or more closely related to oocytes. In addition to the 11 human cancer cell lines mentioned before (11,731 proteins) (35), these included data on human embryonic stem cells (7,952 proteins) (38), human sperm (6,198 …”

“…Before resumption of maturation, oocytes undergo extensive growth, which is accompanied by high transcription rate, while fully matured oocytes become transcriptionally silenced (1,2). Various studies have investigated gene expression programs in human oocytes (3)(4)(5)(6)(7), yet the characterization of translation into functional protein products at different stages of oocyte growth and maturation remains poorly understood. During oocyte growth, many maternally transcribed mRNAs can be stored dispersed throughout the cytoplasm or in localized messenger ribonucleoprotein complexes in a translationally silent state (8).…”

Expression and intracytoplasmic distribution of staufen and calreticulin in maturing human oocytes

“…A wide number of proteins and factors is involved in the process of transport of mRNAs from the oocyte nucleus to the cytoplasm. [16] One of these is represented by STAU, whose function is to bind the mature mRNA and transport it to specific sites of the cytoskeleton, where it promotes anchorage for the translation of the corresponding protein [7].…”

“…All cryopreservation solutions were prepared as described elsewhere (De Santis et al, 2007b) Thawing was conducted at room temperature, with a four step procedure and oocytes were then replaced in culture medium at 37°C for at least 1 h until further evaluation of oocytes degeneration [13,14]. RNA from each pool of oocytes was reverse transcribed (RT) into cDNA in a total reaction mixture volume of 20 μl containing 8.5 μl sterile water, 1 μl of 10 mM dNTP mix, and 1 μl oligo (dT) [12][13][14][15][16][17][18] (500 ng/μl). RT was performed with 200 U of SuperScript II reverse transcriptase (Invitrogen, Italy) for 1 h at 42°C.…”

Oocyte-associated transcription factors in reprogramming after somatic cell nuclear transfer: a review

“…Embryo quality and developmental competence are associated with oocyte maturation [70][71][72]. Mammalian embryos are destined to die unless crucial early developmental events take place to suppress cellular death.…”