Objective: To determine whether human oocytes possess a checkpoint to prevent completion of meiosis I when DNA is damaged. Design: DNA damage is considered a major threat to the establishment of healthy eggs and embryos. Recent studies found that mouse oocytes with damaged DNA can resume meiosis and undergo germinal vesicle breakdown (GVBD), but then arrest in metaphase of meiosis I in a process involving spindle assembly checkpoint (SAC) signaling. Such a mechanism could help prevent the generation of metaphase II (MII) eggs with damaged DNA. Here, we compared the impact of DNA-damaging agents with nondamaged control samples in mouse and human oocytes. Setting: University-affiliated clinic and research center. Patient(s): Patients undergoing ICSI cycles donated GV-stage oocytes after informed consent; 149 human oocytes were collected over 2 years (from 50 patients aged 27-44 years). Interventions(s): Mice and human oocytes were treated with DNA-damaging drugs. Main Outcome Measure(s): Oocytes were monitored to evaluate GVBD and polar body extrusion (PBE), in addition to DNA damage assessment with the use of gH2AX antibodies and confocal microscopy. Result(s): Whereas DNA damage in mouse oocytes delays or prevents oocyte maturation, most human oocytes harboring experimentally induced DNA damage progress through meiosis I and subsequently form an MII egg, revealing the absence of a DNA damageinduced SAC response. Analysis of the resulting MII eggs revealed damaged DNA and chaotic spindle apparatus, despite the oocyte appearing morphologically normal. Conclusion(s): Our data indicate that experimentally induced DNA damage does not prevent PBE in human oocytes and can persist in morphologically normal looking MII eggs. (Fertil Steril Ò 2020;113:1080-89. Ó2020 by American Society for Reproductive Medicine.) El resumen está disponible en Español al final del artículo.
Leptin is an important hormone influencing reproductive function. However, the mechanisms underpinning the role of leptin in the regulation of reproduction remain to be completely deciphered. In this study, our objective is to understand the mechanisms regulating the expression of leptin receptor (Lepr) and its role in ovarian granulosa cells during ovulation. First, granulosa cells were collected from superovulated mice to profile mRNA expression of Lepr isoforms (LeprA and LeprB) throughout follicular development. Expression of LeprA and LeprB was dramatically induced in the granulosa cells of ovulating follicles at 4 h after human chorionic gonadotropin (hCG) treatment. Relative abundance of both mRNA and protein of CCAAT/enhancer-binding protein b (Cebpb) increased in granulosa cells from 1 to 7 h post-hCG. Furthermore, chromatin immunoprecipitation assay confirmed the recruitment of Cebpb to Lepr promoter. Thus, hCG-induced transcription of Lepr appears to be regulated by Cebpb, which led us to hypothesise that Lepr may play a role during ovulation. To test this hypothesis, we used a recently developed pegylated superactive mouse leptin antagonist (PEG-SMLA) to inhibit Lepr signalling during ovulation. I.p. administration of PEG-SMLA (10 mg/g) to superovulated mice reduced ovulation rate by 65% compared with control treatment. Although the maturation stage of the ovulated oocytes remained unaltered, ovulation genes Ptgs2 and Has2 were downregulated in PEG-SMLA-treated mice compared with control mice. These results demonstrate that Lepr is dramatically induced in the granulosa cells of ovulating follicles and this induction of Lepr expression requires the transcription factor Cebpb. Lepr plays a critical role in the process of ovulation by regulating, at least in part, the expression of the important genes involved in the preovulatory maturation of follicles.
The fatty acid binding protein 6 (Fabp6) is commonly regarded as a bile acid binding protein found in the distal portion of the small intestine and has been shown to be important in maintaining bile acid homeostasis. Previous studies have also reported the presence of Fabp6 in human, rat and fish ovaries, but the significance of Fabp6 in this organ is largely unknown. Therefore, we surveyed murine ovaries for Fabp6 gene expression and evaluated its role in ovarian function using mice with whole body Fabp6 deficiency. Here we show that the Fabp6 gene is expressed in granulosa and luteal cells of the mouse ovary. Treatment with gonadotropins stimulated Fabp6 gene expression in large antral follicles. The ovulation rate in response to superovulatory treatment in Fabp6-deficient mice was markedly decreased compared to wildtype (C57BL/6) mice. The results of this study suggest that expression of Fabp6 gene in granulosa cells serves an important and previously unrecognized function in fertility.
Successful ovulation requires the actions of gonadotropins along with those mediated by growth factors binding to their receptor tyrosine kinases (RTKs). There are several growth factors such as epidermal growth factor family ligands and interleukins that play a role during ovulation initiated by the preovulatory surge of luteinizing hormone (LH). The aim of this project was to analyze growth factor signaling pathways induced by LH in mouse granulosa cells. Immature female mice were treated with equine chorionic gonadotropin (eCG) followed 48 hr later by human chorionic gonadotropin (hCG) to induce follicular growth and ovulation. We performed protein array analysis where we identified higher phosphorylation of insulin-like growth factor 1 receptor (IGF1R), the fibroblast growth factor receptor 2 (FGFR2) and ephrin receptor B1 (EPHB1) in granulosa cells at 4 hr post-hCG compared to 0 hr hCG (p < 0.05). We report both a significant increase in transcript abundance (p < 0.05) and the phosphorylation level (p < 0.05) of the IGF1R in granulosa cells at hCG4h. The mRNA abundance of the Fgfr2 and Ephb1 receptors remained unaltered upon hCG treatment. Nonetheless, transcript abundance of the fibroblast growth factor 2 (Fgf2) ligand was elevated at hCG4h (p < 0.01). Based on these results we conclude that the preovulatory LH surge activates signaling pathways of IGF1R through increase in the expression of the Igf1r gene in granulosa cells of ovulating follicles in mice. The LH surge also appears to activate FGFR2 IIIc and EPHB1 signaling, although further investigation is required.
In vitro fertilization (IVF) has been widely used to treat infertile couples. Standardly, IVF protocols start stimulation in the early follicular phase [1]. Centers routinely perform ultrasound on cycle day 2 to 3 to evaluate the endometrial lining, rule out pregnancy, and verify a lack of functional ovarian cysts before starting controlled ovarian stimulation. However, the role of early follicular start is being questioned, with random and luteal phase stimulations being investigated, particularly in centers practicing freeze all protocols to favor implantation [1][2][3]. This is done for both convenience and in cancer patients desiring pre-chemotherapy fertility preservation, who must start urgently [4,5]. In a recent study, patients were divided into three groups based on menstrual cycle phase for commencement of stimulation: the conventional early follicular, late follicular phase, and luteal phase starts. All three groups were comparable in terms of the number of mature oocytes (MII), quantity of embryos and oocytes retrieved, implantation rates, and clinical pregnancy rates [2]. Clearly, a random start for IVF stimulation is interesting in that it will minimize time to initiate stimulation, particularly if the center will perform pre-implantation genetic testing type A or for implantation benefit, freeze all embryos, a trend, which is increasing, particularly in the USA.However, when luteal phase starts, one complication that may arise is that the patient could be unknowingly pregnant. The role of pregnancy on stimulation outcomes has not been investigated. However, we would anticipate that the body has mechanisms in place to prevent double fecundation at different time periods, which would result in two pregnancies of different gestational ages developing concurrently. The role of
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.