Impaired ovarian development and reduced fertility in female mice deficient in Skp2

Aberrantly High FBXO31 Impairs Oocyte Quality in Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI), which is defined as loss of ovarian function that occurs before the age of 40, causes menstrual disturbances, infertility, and diverse health problems in females. Despite the limited understanding of the molecular basis underlying POI pathology, we had previously demonstrated that the cooperation of miR-106a and FBXO31 plays a pivotal role in diminished ovarian reserve (DOR), with FBXO31 serving as a putative target of miR-106a. In this study, we found that FBXO31 is aberrantly expressed in granulosa cells of POI patients, leading to accumulated reactive oxygen species (ROS) and cell apoptosis via the p53/ROS pathway. Furthermore, our results demonstrated that high levels of FBXO31 in mouse ovaries impair oocyte quality. Our study revealed that FBXO31 may serve as a novel indicator and play a significant role in the etiology of POI.

Skp2: A critical molecule for ubiquitination and its role in cancer

The ubiquitin-proteasome system (UPS) is a multi-step process that serves as the primary pathway for protein degradation within cells. UPS activity also plays a crucial role in regulating various life processes, including the cell cycle, signal transduction, DNA repair, and others. The F-box protein Skp2, a crucial member of the UPS, plays a central role in the development of various diseases. Skp2 controls cancer cell growth and drug resistance by ubiquitinating modifications to a variety of proteins. This review emphasizes the multifaceted role of Skp2 in a wide range of cancers and the mechanisms involved, highlighting the potential of Skp2 as a therapeutic target in cancer. Additionally, we describe the impactful influence exerted by Skp2 in various other diseases beyond cancer.

Causal and Candidate Gene Variants in a Large Cohort of Women With Primary Ovarian Insufficiency

CONTEXT

A genetic etiology likely accounts for the majority of unexplained primary ovarian insufficiency (POI).

OBJECTIVE

We hypothesized that heterozygous rare variants and variants in enhanced categories are associated with POI.

DESIGN

The study was an observational study.

SETTING

Subjects were recruited at academic institutions.

PATIENTS

Subjects from Boston (n = 98), the National Institutes of Health and Washington University (n = 98), Pittsburgh (n = 20), Italy (n = 43), and France (n = 32) were diagnosed with POI (amenorrhea with an elevated follicle-stimulating hormone level). Controls were recruited for health in old age or were from the 1000 Genomes Project (total n = 233).

INTERVENTION

We performed whole exome sequencing (WES), and data were analyzed using a rare variant scoring method and a Bayes factor-based framework for identifying genes harboring pathogenic variants. We performed functional studies on identified genes that were not previously implicated in POI in a D. melanogaster model.

MAIN OUTCOME

Genes with rare pathogenic variants and gene sets with increased burden of deleterious variants were identified.

RESULTS

Candidate heterozygous variants were identified in known genes and genes with functional evidence. Gene sets with increased burden of deleterious alleles included the categories transcription and translation, DNA damage and repair, meiosis and cell division. Variants were found in novel genes from the enhanced categories. Functional evidence supported 7 new risk genes for POI (USP36, VCP, WDR33, PIWIL3, NPM2, LLGL1, and BOD1L1).

CONCLUSIONS

Candidate causative variants were identified through WES in women with POI. Aggregating clinical data and genetic risk with a categorical approach may expand the genetic architecture of heterozygous rare gene variants causing risk for POI.

Downregulation of decidual SKP2 is associated with human recurrent miscarriage

BACKGROUND

Recurrent miscarriage (RM) is a very frustrating problem for both couples and clinicians. To date, the etiology of RM remains poorly understood. Decidualization plays a critical role in implantation and the maintenance of pregnancy, and its deficiency is closely correlated with RM. The F-box protein S-phase kinase associated protein 2 (SKP2) is a key component of the SCF-type E3 ubiquitin ligase complex, which is critically involved in ErbB family-induced Akt ubiquitination, aerobic glycolysis and tumorigenesis. SKP2 is pivotal for reproduction, and SKP2-deficient mice show impaired ovarian development and reduced fertility.

METHODS

Here, we investigated the expression and function of SKP2 in human decidualization and its relation with RM. A total of 40 decidual samples were collected. Quantitative PCR analysis, western blot analysis and immunohistochemistry analysis were performed to analyze the differential expression of SKP2 between RM and control cells. For in vitro induction of decidualization, both HESCs (human endometrial stromal cells) cell line and primary ESCs (endometrial stromal cells) were used to analyze the effects of SKP2 on decidualization via siRNA transfection.

RESULTS

Compared to normal pregnant women, the expression of SKP2 was reduced in the decidual tissues from individuals with RM. After in vitro induction of decidualization, knockdown of SKP2 apparently attenuated the decidualization of HESCs and resulted in the downregulation of HOXA10 and FOXM1, which are essential for normal human decidualization. Moreover, our experiments demonstrated that SKP2 silencing reduced the expression of its downstream target GLUT1.

CONCLUSIONS

Our study indicates a functional role of SKP2 in RM: downregulation of SKP2 in RM leads to impaired decidualization and downregulation of GLUT1 and consequently predisposes individuals to RM.

Pathways Involved in Premature Ovarian Failure: A Systematic Review of Experimental Studies

Premature ovarian failure (POF), which may be undetectable for a long time, is associated with impaired fertility. The mechanisms involved in the pathogenesis of POF as well as the concomitant treatments are still unclear. Although many data exist, mainly produced by the study of transgenic animals under various experimental conditions, they remain fragmented. A systematic review of the pathways involved in premature ovarian failure was conducted. Data extraction was performed from experimental studies until 2019. The molecular processes and their correlation with the follicular developmental stage have been described. Furthermore, the effects in other cells, such as oocytes, granulosa and theca cells have been reported. An overall estimation was conducted.

The Skp2 Pathway: A Critical Target for Cancer Therapy

Strictly regulated protein degradation by ubiquitin-proteasome system (UPS) is essential for various cellular processes whose dysregulation is linked to serious diseases including cancer. Skp2, a well characterized component of Skp2-SCF E3 ligase complex, is able to conjugate both K48-linked ubiquitin chains and K63-linked ubiquitin chains on its diverse substrates, inducing proteasome mediated proteolysis or modulating the function of tagged substrates respectively. Overexpression of Skp2 is observed in various human cancers associated with poor survival and adverse therapeutic outcomes, which in turn suggests that Skp2 engages in tumorigenic activity. To that end, the oncogenic properties of Skp2 are demonstrated by various genetic mouse models, highlighting the potential of Skp2 as a target for tackling cancer. In this article, we will describe the downstream substrates of Skp2 as well as upstream regulators for Skp2-SCF complex activity. We will further summarize the comprehensive oncogenic functions of Skp2 while describing diverse strategies and therapeutic platforms currently available for developing Skp2 inhibitors.

Diverse roles for CDK-associated activity during spermatogenesis

The primary function of cyclin-dependent kinases (CDKs) in complex with their activating cyclin partners is to promote mitotic division in somatic cells. This canonical cell cycle-associated activity is also crucial for fertility as it allows the proliferation and differentiation of stem cells within the reproductive organs to generate meiotically competent cells. Intriguingly, several CDKs exhibit meiosis-specific functions and are essential for the completion of the two reductional meiotic divisions required to generate haploid gametes. These meiosis-specific functions are mediated by both known CDK/cyclin complexes and meiosis-specific CDK-regulators and are important for a variety of processes during meiotic prophase. The majority of meiotic defects observed upon deletion of these proteins occur during the extended prophase I of the first meiotic division. Importantly a lack of redundancy is seen within the meiotic arrest phenotypes described for many of these proteins, suggesting intricate layers of cell cycle control are required for normal meiotic progression. Using the process of male germ cell development (spermatogenesis) as a reference, this review seeks to highlight the diverse roles of selected CDKs their activators, and their regulators during gametogenesis.

RNA-sequencing analysis of umbilical cord plasma microRNAs from healthy newborns

MicroRNAs are a class of small non-coding RNA that regulate gene expression at a post-transcriptional level. MicroRNAs have been identified in various body fluids under normal conditions and their stability as well as their dysregulation in disease has led to ongoing interest in their diagnostic and prognostic potential. Circulating microRNAs may be valuable predictors of early-life complications such as birth asphyxia or neonatal seizures but there are relatively few data on microRNA content in plasma from healthy babies. Here we performed small RNA-sequencing analysis of plasma processed from umbilical cord blood in a set of healthy newborns. MicroRNA levels in umbilical cord plasma of four male and four female healthy babies, from two different centres were profiled. A total of 1,004 individual microRNAs were identified, which ranged from 426 to 659 per sample, of which 269 microRNAs were common to all eight samples. Many of these microRNAs are highly expressed and consistent with previous studies using other high throughput platforms. While overall microRNA expression did not differ between male and female cord blood plasma, we did detect differentially edited microRNAs in female plasma compared to male. Of note, and consistent with other studies of this type, adenylation and uridylation were the two most prominent forms of editing. Six microRNAs, miR-128-3p, miR-29a-3p, miR-9-5p, miR-218-5p, 204-5p and miR-132-3p were consistently both uridylated and adenylated in female cord blood plasma. These results provide a benchmark for microRNA profiling and biomarker discovery using umbilical cord plasma and can be used as comparative data for future biomarker profiles from complicated births or those with early-life developmental disorders.

Uncovering the Changing Gene Expression Profile of Honeybee (Apis mellifera) Worker Larvae Transplanted to Queen Cells

The reproductive division of labor, based on caste differentiation in social insects, is of great significance in evolution. Generally, a healthy bee colony consists of a queen and numerous workers and drones. Despite being genetically identical, the queen and workers exhibit striking differences in morphology, behavior, and lifespan. The fertilized eggs and larvae selectively develop into queen and worker bees depending on the local nutrition and environment. Bee worker larvae that are transplanted within 3 days of age to queen cells of a bee colony can develop into queens with mature ovaries. This phenomenon is important to understand the regulatory mechanisms of caste differentiation. In this study, we transplanted worker larvae (Apis mellifera) at the age of 1 (L1), 2 (L2), and 3 days (L3) into queen cells until the age of 4 days. Subsequently, genetic changes in these larvae were evaluated. The results revealed that the number of differentially expressed genes (DEGs) in L1 vs. L3 was more than that in L1 vs. L2. Furthermore, many of the genes that were downregulated are mostly involved in metabolism, body development, reproductive ability, and longevity, indicating that these functions decreased with the age of transplantation of the larvae. Moreover, these functions may be critical for worker larvae to undergo the developmental path to become queens. We also found that the DEGs of L1 vs. L2 and L1 vs. L3 were enriched in the MAPK, FoxO, mTOR, Wnt, TGF-beta Hedgehog Toll and Imd, and Hippo signaling pathways. Gene ontology analysis indicated that some genes are simultaneously involved in different biological pathways; through these genes, the pathways formed a mutual regulatory network. Casein kinase 1 (CK 1) was predicted to participate in the FoxO, Wnt, Hedgehog, and Hippo signaling pathways. The results suggest that these pathways cross talked through the network to modify the development of larvae and that CK 1 is an important liaison. The results provide valuable information regarding the regulatory mechanism of environmental factors affecting queen development, thus, amplifying the understanding of caste differentiation in bees.

Effects of Bushen Tianjing Recipe in a rat model of tripterygium glycoside-induced premature ovarian failure

Background

Bushen Tianjing Recipe (BTR) is a traditional Chinese herbal medicine that has been prescribed for premature ovarian failure (POF) for decades in China. Nevertheless, little is known regarding its underlying molecular mechanism. In the present study, we investigated the effects of BTR in a tripterygium glycoside (TG)-induced-POF rat model.

Methods

Three doses of BTR were administered via intragastric gavage to adult female Sprague–Dawley (SD) rats with TG-induced POF. After 15 days of treatment, the estrous cycle was examined by vaginal smear analysis. Serum levels of estradiol, follicle-stimulating hormone, progesterone, and testosterone were measured by radioimmunoassay. Histological analysis and assessment of apoptosis were performed after hematoxylin and eosin staining of ovarian tissue sections. The expression of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor 2 (VEGFR2), anti-apoptotic factor Bcl-2, and pro-apoptotic factors Bax and caspase 3 in ovaries of animals was examined by an immunohistochemistry process.

Results

BTR not only reverted an abnormal estrous cycle and decreased the ovary index in POF rats but also improved the abnormal secretion of reproductive hormones associated with POF. In addition, treatment with BTR can protect ovaries from TG-induced damage, induce intraovarian expression of VEGF and VEGFR2, and regulate intraovarian expression of apoptosis-related proteins.

Conclusions

Our results show that BTR is effective in the treatment of TG-induced POF rats. Promotion of angiogenesis and anti-apoptosis are most likely to contribute to the effects of BTR against POF.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-017-0131-3) contains supplementary material, which is available to authorized users.

Genome-Wide Identification and Expression of Xenopus F-Box Family of Proteins

Protein degradation via the multistep ubiquitin/26S proteasome pathway is a rapid way to alter the protein profile and drive cell processes and developmental changes. Many key regulators of embryonic development are targeted for degradation by E3 ubiquitin ligases. The most studied family of E3 ubiquitin ligases is the SCF ubiquitin ligases, which use F-box adaptor proteins to recognize and recruit target proteins. Here, we used a bioinformatics screen and phylogenetic analysis to identify and annotate the family of F-box proteins in the Xenopus tropicalis genome. To shed light on the function of the F-box proteins, we analyzed expression of F-box genes during early stages of Xenopus development. Many F-box genes are broadly expressed with expression domains localized to diverse tissues including brain, spinal cord, eye, neural crest derivatives, somites, kidneys, and heart. All together, our genome-wide identification and expression profiling of the Xenopus F-box family of proteins provide a foundation for future research aimed to identify the precise role of F-box dependent E3 ubiquitin ligases and their targets in the regulatory circuits of development.

It is not all about BRCA: Cullin-Ring ubiquitin Ligases in ovarian cancer

Mutations in the BRCA1 and BRCA2 genes predispose individuals to the development of breast and ovarian cancers. As a result, biochemical functions of BRCA1 and BRCA2 proteins are being characterised in great detail. These studies have prompted the use of PARP inhibitors to treat BRCA1 and BRCA2-deficient ovarian cancers. This example of synthetic lethality represents a conceptual progress made recently in the approach to cancer treatment and is being currently tested in multiple clinical trials. Other than BRCA1 and BRCA2, many other factors might influence the survival of ovarian cancer patients. Currently, ovarian cancer remains the fifth most common cancer in the United Kingdom among women. Recent evidence suggests benefit in the modulation of the ubiquitin-proteasome system for the treatment of ovarian cancer. In this manuscript, we review the role of Cullin-Ring ubiquitin Ligases (CRLs) in the pathogenesis of ovarian cancer and their potential therapeutic exploitation. CRLs comprise a large family of proteins that, like kinases, might represent ideal candidates for targeted therapy and provide a large repertoire for the development of new anti-cancer compounds.

Polyploid giant cancer cells with budding and the expression of cyclin E, S-phase kinase-associated protein 2, stathmin associated with the grading and metastasis in serous ovarian tumor

BACKGROUND

We previously reported that polyploid giant cancer cells (PGCCs) exhibit cancer stem cell properties and express cell cycle-related proteins. HEY PGCCs induced by cobalt chloride generated daughter cells and the daughter cells had a strong migratory and invasive ability. This study is to compare the expression of cyclin E, S-phase kinase-associated protein 2 (SKP2), and stathmin between PGCCs with budding and control HEY cells, and determine the clinicopathological significance of cell cycle-related protein expression in ovarian tumors.

METHODS

We used western blot and immunocytochemical staining to compare the expression levels of cyclin E, SKP2 and stathmin between PGCC with budding daughter cells and control HEY cells. In addition, immunohistochemical staining for cyclin E, SKP2 and stathmin was performed on a total of 80 paraffin-embedded serous ovarian tumor tissue samples. The samples included 21 cases of primary high-grade carcinoma (group I) and their metastatic tumors (group II), 26 cases of primary low-grade carcinoma without metastasis (group III), and 12 cases of serous borderline cystadenoma (group IV).

RESULTS

Single PGCC with budding in the stroma showed high correlation with the metastasis of ovarian carcinoma. Group I had a significantly higher number of single PGCCs with budding in the stroma than group III (85.71% [18/21] vs. 23.08% [6/26] cases; χ2 = 18.240, P = 0.000). The expression of cyclin E, SKP2, and stathmin was compared among the four groups. The expression levels of cyclin E, SKP2, and stathmin increased with the malignant grade of ovarian tumors and group II had the highest expression levels. The expression of cyclin E (χ2 = 17.985, P = 0.000), SKP2 (χ2 = 12.384, P = 0.000), and stathmin (χ2 = 20.226, P = 0.000) was significantly different among the 4 groups.

CONCLUSIONS

These data suggest that the cell cycle-related proteins cyclin E, SKP2, and stathmin may be valuable biomarkers to evaluate the metastasis in patients with ovarian serous carcinoma.

Mutational analysis of SKP2 and P27 in Chinese Han women with premature ovarian failure

P27 and SKP2, a major regulator of P27, play a crucial role in ovarian function in mice. Both P27-deficient and SKP2-deficient female mice develop premature ovarian failure (POF). The coding regions of SKP2 and P27 were examined in 200 Chinese women with POF and 200 control volunteers. This study is the first to investigate SKP2 in POF. No plausible pathogenic mutations were detected. The results suggest that mutations in SKP2 and P27 are not common in Chinese Han women with POF.

Genetically engineered mouse models for functional studies of SKP1-CUL1-F-box-protein (SCF) E3 ubiquitin ligases

The SCF (SKP1 (S-phase-kinase-associated protein 1), Cullin-1, F-box protein) E3 ubiquitin ligases, the founding member of Cullin-RING ligases (CRLs), are the largest family of E3 ubiquitin ligases in mammals. Each individual SCF E3 ligase consists of one adaptor protein SKP1, one scaffold protein cullin-1 (the first family member of the eight cullins), one F-box protein out of 69 family members, and one out of two RING (Really Interesting New Gene) family proteins RBX1/ROC1 or RBX2/ROC2/SAG/RNF7. Various combinations of these four components construct a large number of SCF E3s that promote the degradation of many key regulatory proteins in cell-context, temporally, and spatially dependent manners, thus controlling precisely numerous important cellular processes, including cell cycle progression, apoptosis, gene transcription, signal transduction, DNA replication, maintenance of genome integrity, and tumorigenesis. To understand how the SCF E3 ligases regulate these cellular processes and embryonic development under in vivo physiological conditions, a number of mouse models with transgenic (Tg) expression or targeted deletion of components of SCF have been established and characterized. In this review, we will provide a brief introduction to the ubiquitin-proteasome system (UPS) and the SCF E3 ubiquitin ligases, followed by a comprehensive overview on the existing Tg and knockout (KO) mouse models of the SCF E3s, and discuss the role of each component in mouse embryogenesis, cell proliferation, apoptosis, carcinogenesis, as well as other pathogenic processes associated with human diseases. We will end with a brief discussion on the future directions of this research area and the potential applications of the knowledge gained to more effective therapeutic interventions of human diseases.