Defining the Program of Maternal mRNA Translation during In vitro Maturation using a Single Oocyte Reporter Assay. Costermans NGJ et al. (2021) Events associated with oocyte nuclear maturation have been well described. However, much less is known about the molecular pathways and processes that take place in the cytoplasm in preparation for fertilization and acquisition of totipotency. During oocyte maturation, changes in gene expression depend exclusively on the translation and degradation of maternal messenger RNAs (mRNAs) rather than on transcription. Execution of the translational program, therefore, plays a key role in establishing oocyte developmental competence to sustain embryo development. This paper is part of a focus on defining the program of maternal mRNA translation that takes place during meiotic maturation and at the oocyte-to-zygote transition. In this method paper, a strategy is presented to study the regulation of translation of target mRNAs during in vitro oocyte maturation. Here, a Ypet reporter is fused to the 3' untranslated region (UTR) of the gene of interest and then micro-injected into oocytes together with polyadenylated mRNA encoding for mCherry to control for injected volume. By using time-lapse microscopy to measure reporter accumulation, translation rates are calculated at different transitions during oocyte meiotic maturation. Here, the protocols for oocyte isolation and injection, time-lapse recording, and data analysis have been described, using the Ypet/interleukin-7 (IL-7)-3' UTR reporter as an example.//////////////////
NCBI Summary:
The protein encoded by this gene is a cytokine important for B and T cell development. This cytokine and the hepatocyte growth factor (HGF) form a heterodimer that functions as a pre-pro-B cell growth-stimulating factor. IL7 is found to be a cofactor for V(D)J rearrangement of the T cell receptor beta (TCRB) during early T cell development. This cytokine can be produced locally by intestinal epithelial and epithelial goblet cells, and may serve as a regulatory factor for intestinal mucosal lymphocytes. IL7 plays an essential role in lymphoid cell survival, and in the maintenance of naive and memory T cells. Alternative splicing results in multiple transcript variants encoding distinct isoforms. Additional splice variants have been described but their presence in normal tissues has not been confirmed. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can be a potent inducer of proinflammatory cytokines and chemokines which may defend against the infection, but may also mediate destructive lung injury. Elevated serum IL7 levels, together with several other circulating cytokines and chemokines, has been found to be associated with the severity of Coronavirus Disease 19 (COVID-19). [provided by RefSeq, Jul 2020]
Cumulus expansion, Follicle atresia, Luteinization, Oogenesis, Oocyte maturation, Early embryo development
Comment
Interleukin-7 improves in vitro maturation of ovine cumulus-oocyte complexes in a dose dependent manner. Javvaji PK et al. (2018) Interleukin-7 (IL-7) mediated signals are linked to development, proliferation, survival and differentiation of cells. Recent evidences indicate its role in oocyte maturation process as well. Nevertheless, the underlying mechanisms of IL-7 involvement in oocyte maturation are not well characterized. In addition, currently no information is available on the effect of exogenous IL-7 on oocyte maturation in ovine or any other species. In this study, the effect of IL-7 supplementation during in vitro maturation (IVM) on the maturation rate, production of reactive oxygen species (ROS) and gene expression of ovine cumulus-oocyte complexes (COC) was assessed. IL-7 (0.5, 1, 2, 5 and 10 ng/ml) was supplemented in IVM medium at the beginning (0 h) and maturation rate of COC was assessed at the completion of IVM (24 h). The maturation rate (%) was found significantly (P = 0.000) greater with the 1 ng/ml of IL-7 supplementation (69.5) than control (60.0). In contrast, the maturation rate was reduced significantly (P = 0.000) with the 2 (47.1), 5 (39.2) and 10 ng/ml (39.1) of IL-7 as compared to the control. The level of intracellular ROS in the matured COC was found considerably higher with the 5 ng/ml of IL-7 followed by 1 ng/ml of IL-7 and control. It was evident that in the presence of superoxide dismutase-inhibitor, 1 ng/ml of IL-7 did not stimulate oocyte maturation. In contrast, oocyte maturation was improved with 5 ng/ml of IL-7 supplementation in the presence of NADPH-oxidase-inhibitor. IL-7 supplementation influenced gene expression in COC in a dose and time dependant manner. The expression of genes related to ROS production and apoptosis were upregulated and the genes associated with antioxidant mechanisms were downregulated noticeably with the supplementation of 5 ng/ml of IL-7. In conclusion, IL-7 at low concentration was beneficial for oocyte maturation, which was likely mediated through the favourable level of intracellular ROS and antioxidant mechanisms. In contrast, the detrimental effects of greater IL-7 concentrations on oocyte maturation were possibly arbitrated through the ROS-mediated oxidative stress, compromised antioxidant mechanism and stimulated apoptotic signalling.//////////////////
Oocyte-Expressed Interleukin 7 Suppresses Granulosa Cell Apoptosis and Promotes Oocyte Maturation in Rats. Cheng Y et al. Development of ovarian follicles is regulated by pituitary-derived gonadotropins together with local ovarian paracrine factors. Based on DNA microarray data, we performed reverse transcription-PCR and immunostaining to demonstrate the expression of interleukin 7 transcripts in oocytes of preantral, antral and preovulatory follicles in rats. We also found the expression of interleukin 7 receptor (IL7R) and the co-receptor interleukin 2 receptor gamma (IL2RG) in granulosa cells, cumulus cells, and preovulatory oocytes. In cultured rat granulosa cells obtained from early antral and preovulatory follicles, treatment with interleukin 7 stimulated the phosphorylation of AKT, GSK3B, and STAT5 proteins in a time- and dose-dependent manner. Furthermore, measurement of mitochondrial reductase activity indicated that treatment with interleukin 7, similar to gonadotropins, increased the number of viable granulosa cells during a 24h culture period. Furthermore, monitoring of the activities of apoptotic enzymes caspase-3/7 indicated that treatment with interleukin 7 suppressed apoptosis of cultured granulosa cells from both antral and preovulatory follicles following serum withdrawal. The apoptosis-suppressing actions of interleukin 7 were blocked by an inhibitor of the phosphoinositol-3-kinase (PIK3)/AKT pathway. Furthermore, treatment of cultured preovulatory follicles with interleukin 7, like hCG, induced germinal vesicle breakdown of oocytes. The stimulatory effect of interleukin 7 was also blocked by inhibitors of the PIK3/AKT pathway. The present findings suggest that oocyte-derived interleukin 7 could act on neighboring granulosa cells as a survival factor and also promote the nuclear maturation of preovulatory oocytes through activation of the PIK3/AKT pathway.////////Dynamic secretion during meiotic reentry integrates the function of the oocyte and cumulus cells. Cakmak H et al. (2016) The differentiation of the female gamete into a developmentally competent oocyte relies on the protected environment of the ovarian follicle. The oocyte plays a key role in establishing this microenvironment by releasing paracrine factors that control the functions of surrounding somatic cells. Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are secreted during follicle growth and play pivotal roles in this local regulation. The current view is that the function of these secreted factors declines in the periovulatory period when the oocyte reenters the meiotic cell cycle. Here, we provide evidence that oocyte reentry into meiosis is instead associated with a shift in the pattern of secretion with a new set of bioactive molecules synthesized before ovulation. Using interleukin 7 (IL7) as a prototypic secreted factor, we show that its secretion is dependent on activation of mRNA translation in synchrony with the cell cycle and that its translation is under the control of somatic cells. IL7 is part of a local feedback loop with the soma because it regulates cumulus cell replication. Similar conclusions are reached when IL7 secretion is measured in human follicular fluid during in vitro fertilization cycles. IL7 concentration in the follicular fluid correlates with the oocyte ability to reach the MII stage of maturation. These findings are consistent with the hypothesis that a new set of local factors is secreted by the oocyte during ovulation. These dynamic secretions are likely critical for promoting the final stages of maturation and oocyte developmental competence.//////////////////
Maternal gene transcription in mouse oocytes: genes implicated in oocyte maturation and fertilization. Cui XS et al. Maternal gene expression is an important biological process in oocyte maturation and early cleavage. To gain insights into oocyte maturation and early embryo development, we used microarray analysis to compare the gene expression profiles of germinal vesicle (GV)- and metaphase II (MII)-stage oocytes. The differences in spot intensities were normalized and grouped using the Avadis Prophetic software platform. Of the 12164 genes examined, we found 1682 genes with more highly expression in GV-stage oocytes than in MII-stage oocytes, while 1936 genes were more highly expressed in MII-stage oocytes (P<0.05). The genes were grouped on the basis of the Panther classification system according to their involvement in particular biological processes. The genes that were up-regulated in GV oocytes were more likely to be involved in protein metabolism and modification, the mitotic cell cycle, electron transport, or fertilization or belong to the microtubule/cytoskeletal protein family. The genes specifically upregulated in the MII oocytes were more likely to be involved in DNA replication, amino acid metabolism, or expression of G protein-coupled receptors and signaling molecules. Identification of genes that are preferentially expressed at particular oocyte maturation stages provides insights into the complex gene regulatory networks that drive oocyte maturation and fertilization. IL7 is 4.5 fold higher in MII than GV stage.
Expression regulated by
FSH
Comment
FSH regulates mRNA translation in mouse oocytes and promotes developmental competence. Franciosi F et al. (2015) A major challenge in assisted reproductive technology is to develop conditions for in vitro oocyte maturation yielding high-quality eggs. Efforts are underway to assess whether known hormonal and local factors play a role in oocyte developmental competence and to identify the molecular mechanism involved. Here, we have tested the hypothesis that FSH improves oocyte developmental competence by regulating the translational program in the oocyte. Accumulation of oocyte proteins (TPX2 and IL7) associated with improved oocyte quality is increased when cumulus/oocyte complexes are incubated with FSH. This increase is due to enhanced translation of the corresponding mRNAs, as indicated by microinjection of constructs where the 3`UTR of the Tpx2 or Il7 transcripts is fused to the luciferase reporter. A transient activation of the PI3K/AKT cascade in the oocyte preceded the increase in translation. When the EGF receptor is down-regulated in follicular cells, the FSH-induced rate of maternal mRNA translation and AKT activation were lost, demonstrating that the effects of FSH are indirect and require EGFR-signaling in the somatic compartment. Using Pten(fl/fl):Zp3cre oocytes where AKT is constitutively activated, translation of reporters was increased and was no longer sensitive to FSH stimulation. More importantly, the oocytes lacking Pten showed increased developmental competence even when cultured in the absence of FSH or growth factors. Thus, we demonstrate that FSH intersects with the follicular EGF-network to activate the PI3K/AKT cascade in the oocyte to control translation and developmental competence. These findings provide a molecular rationale for the use of FSH to improve egg quality.//////////////////
Ovarian localization
Oocyte, Follicular Fluid
Comment
Role of cytokines in the regulation of reproductive function. Ostanin AA et al. The levels of 17 cytokines in the follicular fluid were measured by multiplex proteome analysis at the peak of stimulated ovulation during the in vitro fertilization cycle. In patients with ineffective folliculogenesis, the concentrations of IL-2, IL-4, IL-7, and granulocytic CSF in the follicular fluid were significantly lower than in women with greater mean number of collected oocytes. It was shown that multicomponent cytokine deficit was associated with lower production of high quality oocytes and lower efficiency of fertilization of the resultant oocytes in vitro. The absence of pregnancy after in vitro fertilization cycle is associated with lower levels of IL-2, IL-4, IL-7, granulocytic CSF, and macrophagic inflammatory protein 1b in combination with elevated contents of IL-8 and IL-13. The results attest to an important role of cytokines in the regulation of oogenesis and in preparation of the endometrium to implantation of the embryo.
Found in an ovary DNA array.
Genomewide discovery and classification of candidate ovarian fertility genes in the mouse. Gallardo TD et al. Female infertility syndromes are among the most prevalent chronic health disorders in women, but their genetic basis remains unknown because of uncertainty regarding the number and identity of ovarian factors controlling the assembly, preservation, and maturation of ovarian follicles. To systematically discover ovarian fertility genes en masse, we employed a mouse model (Foxo3) in which follicles are assembled normally but then undergo synchronous activation. We developed a microarray-based approach for the systematic discovery of tissue-specific genes and, by applying it to Foxo3 ovaries and other samples, defined a surprisingly large set of ovarian factors (n = 348, approximately 1% of the mouse genome). This set included the vast majority of known ovarian factors, 44% of which when mutated produce female sterility phenotypes, but most were novel. Comparative profiling of other tissues, including microdissected oocytes and somatic cells, revealed distinct gene classes and provided new insights into oogenesis and ovarian function, demonstrating the utility of our approach for tissue-specific gene discovery. This study will thus facilitate comprehensive analyses of follicle development, ovarian function, and female infertility. This is an oocyte-specific gene.
Follicle stages
Comment
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: fertile Comment: Arrested B lymphopoiesis and persistence of activated B cells in adult interleukin 7(-/)- mice. Carvalho TL et al. Interleukin 7 is a crucial factor for the development of murine T and B lymphocytes. We now report that, in the absence of interleukin 7, B lymphocyte production takes place exclusively during fetal and perinatal life, ceasing after 7 wk of age. In peripheral organs, however, the pool of B lymphocytes is stable throughout adult life and consists only of cells that belong to the B1 and marginal zone (MZ) compartments. This is accompanied by a 50-fold increase in the frequency of immunoglobulin (Ig)M- and IgG-secreting cells, and the concentration of serum immunoglobulins is increased three- to fivefold. Both the MZ phenotype and the increase in serum IgM are T cell independent. These findings reveal a previously undescribed pathway of B lymphopoiesis that is active in early life and is interleukin 7 independent. This pathway generates B1 cells and a normal sized MZ B lymphocyte compartment.