Polo-like kinase 1 promotes Cdc42-induced actin polymerization for asymmetric division in oocytes.

Polo-like kinase I (Plk1) is a highly conserved seronine/threonine kinase essential in meiosis and mitosis for spindle formation and cytokinesis. Here, through temporal application of Plk1 inhibitors, we identify a new role for Plk1 in the establishment of cortical polarity essential for highly asymmetric cell divisions of oocyte meiosis. Application of Plk1 inhibitors in late metaphase I abolishes pPlk1 from spindle poles and prevents the induction of actin polymerization at the cortex through inhibition of local recruitment of Cdc42 and Neuronal Wiskott-Aldrich Syndrome protein (N-WASP). By contrast, an already established polar actin cortex is insensitive to Plk1 inhibitors, but if the polar cortex is first depolymerized, Plk1 inhibitors completely prevent its restoration. Thus, Plk1 is essential for establishment but not maintenance of cortical actin polarity. These findings indicate that Plk1 regulates recruitment of Cdc42 and N-Wasp to coordinate cortical polarity and asymmetric cell division.

Depletion of oocyte dynamin-related protein 1 shows maternal-effect abnormalities in embryonic development.

Eggs contain about 200,000 mitochondria that generate adenosine triphosphate and metabolites essential for oocyte development. Mitochondria also integrate metabolism and transcription via metabolites that regulate epigenetic modifiers, but there is no direct evidence linking oocyte mitochondrial function to the maternal epigenome and subsequent embryo development. Here, we have disrupted oocyte mitochondrial function via deletion of the mitochondrial fission factor Drp1. Fission-deficient oocytes exhibit a high frequency of failure in peri- and postimplantation development. This is associated with altered mitochondrial function, changes in the oocyte transcriptome and proteome, altered subcortical maternal complex, and a decrease in oocyte DNA methylation and H3K27me3. Transplanting pronuclei of fertilized Drp1 knockout oocytes to normal ooplasm fails to rescue embryonic lethality. We conclude that mitochondrial function plays a role in establishing the maternal epigenome, with serious consequences for embryo development.

Oocyte mitochondria-key regulators of oocyte function and potential therapeutic targets for improving fertility.

The development of oocytes and early embryos is dependent on mitochondrial ATP production. This reliance on mitochondrial activity, together with the exclusively maternal inheritance of mitochondria in development, places mitochondria as central regulators of both fertility and transgenerational inheritance mechanisms. Mitochondrial mass and mtDNA content massively increase during oocyte growth. They are highly dynamic organelles and oocyte maturation is accompanied by mitochondrial trafficking around subcellular compartments. Due to their key roles in generation of ATP and reactive oxygen species (ROS), oocyte mitochondrial defects have largely been linked with energy deficiency and oxidative stress. Pharmacological treatments and mitochondrial supplementation have been proposed to improve oocyte quality and fertility by enhancing ATP generation and reducing ROS levels. More recently, the role of mitochondria-derived metabolites in controlling epigenetic modifiers has provided a mechanistic basis for mitochondria-nuclear crosstalk, allowing adaptation of gene expression to specific metabolic states. Here, we discuss the multi-faceted mechanisms by which mitochondrial function influence oocyte quality, as well as longer-term developmental events within and across generations.

HENMT1 is involved in the maintenance of normal female fertility in the mouse.

PIWI-interacting small RNAs (piRNAs) maintain genome stability in animal germ cells, with a predominant role in silencing transposable elements. Mutations in the piRNA pathway in the mouse uniformly lead to failed spermatogenesis and male sterility. By contrast, mutant females are fertile. In keeping with this paradigm, we previously reported male sterility and female fertility associated with loss of the enzyme HENMT1, which is responsible for stabilising piRNAs through the catalysation of 3'-terminal 2'-O-methylation. However, the Henmt1 mutant females were poor breeders, suggesting they could be subfertile. Therefore, we investigated oogenesis and female fertility in these mice in greater detail. Here, we show that mutant females indeed have a 3- to 4-fold reduction in follicle number and reduced litter sizes. In addition, meiosis-II mutant oocytes display various spindle abnormalities and have a dramatically altered transcriptome which includes a down-regulation of transcripts required for microtubule function. This down-regulation could explain the spindle defects observed with consequent reductions in litter size. We suggest these various effects on oogenesis could be exacerbated by asynapsis, an apparently universal feature of piRNA mutants of both sexes. Our findings reveal that loss of the piRNA pathway in females has significant functional consequences.

Mitochondria-targeted therapeutics, MitoQ and BGP-15, reverse aging-associated meiotic spindle defects in mouse and human oocytes.

STUDY QUESTION: Do mitochondria-targeted therapies reverse ageing- and oxidative stress-induced spindle defects in oocytes from mice and humans? SUMMARY ANSWER: Exposure to MitoQ or BGP-15 during IVM protected against spindle and chromosomal defects in mouse oocytes exposed to oxidative stress or derived from reproductively aged mice whilst MitoQ promoted nuclear maturation and protected against chromosomal misalignments in human oocytes. WHAT IS KNOWN ALREADY: Spindle and chromosomal abnormalities in oocytes are more prevalent with maternal aging, increasing the risk of aneuploidy, miscarriage and genetic disorders such as Down's syndrome. The origin of compromised oocyte function may be founded in mitochondrial dysfunction and increased reactive oxygen species (ROS). STUDY DESIGN, SIZE, DURATION: Oocytes from young and old mice were treated with MitoQ and/or BGP-15 during IVM. To directly induce mitochondrial dysfunction, oocytes were treated with H2O2, and then treated the MitoQ and/or BGP-15. Immature human oocytes were cultured with or without MitoQ. Each experiment was repeated at least three times, and data were analyzed by unpaired-sample t-test or chi-square test. PARTICIPANTS/MATERIALS, SETTING, METHODS: Immature germinal vesicle (GV) stage oocytes from 1-, 12- and 18-month-old mice were obtained from preovulatory ovarian follicles. Oocytes were treated with MitoQ and/or BGP-15 during IVM. GV-stage human oocytes were cultured with or without MitoQ. Mitochondrial membrane potential and mitochondrial ROS were measured by live-cell imaging. Meiotic spindle and chromosome alignments were visualized by immunofluorescent labeling of fixed oocytes and the 3-dimensional images were analyzed by Imaris. MAIN RESULTS AND THE ROLE OF CHANCE: MitoQ or BGP-15 during IVM protects against spindle and chromosomal defects in oocytes exposed to oxidative stress and in oocytes from aged mice (P < 0.001). In human oocytes, the presence of MitoQ during IVM promoted nuclear maturation and had a similar positive effect in protecting against chromosomal misalignments (P < 0.001). LIMITATIONS, REASONS FOR CAUTION: Our study identifies two excellent candidates that may help to improve fertility in older women. However, these potential therapies must be tested for efficacy in clinical IVM systems, and undergo thorough examination of resultant offspring in preclinical models before utilization. WIDER IMPLICATIONS OF THE FINDINGS: Our results using in-vitro systems for oocyte maturation in both mouse and human provide proof of principle that mitochondrially targeted molecules such as MitoQ and BGP-15 may represent a novel therapeutic approach against maternal aging-related spindle and chromosomal abnormalities. STUDY FUNDING/COMPETING INTEREST(S): The project was financially supported by the National Health and Medical Research Council and Australian Research Council, Australia. U.A.-Z. was supported by the Iraqi Higher Education and Scientific Research Ministry PhD scholarship and O.C. was supported by TUBITAK-1059B191601275. M.P.M. consults for MitoQ Inc. and holds patents in mitochondria-targeted therapies. R.L.R. is an inventor on patents relating to the use of BGP-15 to improve gamete quality. TRIAL REGISTRATION NUMBER: N/A.

Changes in subcellular structures and states of pumilio 1 regulate the translation of target Mad2 and cyclin B1 mRNAs.

Temporal and spatial control of mRNA translation has emerged as a major mechanism for promoting diverse biological processes. However, the molecular nature of temporal and spatial control of translation remains unclear. In oocytes, many mRNAs are deposited as a translationally repressed form and are translated at appropriate times to promote the progression of meiosis and development. Here, we show that changes in subcellular structures and states of the RNA-binding protein pumilio 1 (Pum1) regulate the translation of target mRNAs and progression of oocyte maturation. Pum1 was shown to bind to Mad2 (also known as Mad2l1) and cyclin B1 mRNAs, assemble highly clustered aggregates, and surround Mad2 and cyclin B1 RNA granules in mouse oocytes. These Pum1 aggregates were dissolved prior to the translational activation of target mRNAs, possibly through phosphorylation. Stabilization of Pum1 aggregates prevented the translational activation of target mRNAs and progression of oocyte maturation. Together, our results provide an aggregation-dissolution model for the temporal and spatial control of translation.

Parameter estimation for a point-source diffusion-decay morphogen model.

In this paper we present a novel method for finding unknown parameters for an unknown morphogen. We postulate the existence of an unknown morphogen in a given three-dimensional domain due to the spontaneous arrangement of a downstream species on the domain boundary for which data is known. Assuming a modified Helmholtz model for the morphogen and that it is produced from a single source in the domain, our method accurately estimates the source location and other model parameters. Notably, our method does not require the forward solution of the model to be computed which can often be a challenge for three-dimensional PDE model parameter fitting. Instead, an extension is made from the problem domain to an infinite domain and the analytic nature of the fundamental solution is exploited. We explore in this manuscript strategies for best conditioning the problem and rigorously explore the accuracy of the method on two test problems. Our tests focus on the effect of source location on accuracy but also the robustness of the algorithm to experimental noise.

Label-free in vivo Raman microspectroscopic imaging of the macromolecular architecture of oocytes.

Confocal Raman spectroscopy (CRS) can provide information about oocyte competency through measurement of changes in the macromolecular architecture during oocyte development and maturation. Hitherto most spectroscopic studies have been limited to fixed oocytes due to the inherent difficulties working with live cells. Here we report the first three-dimensional images of living murine oocytes using CRS. We show that fixation induces significant changes in the macromolecular chemistry compared to living oocytes. A band at 1602 cm-1, assigned to a marker for mitochondria function was found in living oocytes but absent from fixed oocytes providing an in vivo marker. Fixation resulted in significant changes in protein and nucleic acid bands and the spatial distribution of organelles. Raman imaging of Metaphase I and II (MI, MII) and germinal vesicle stage oocytes showed changes in nuclear organisation and cytoplasm macromolecular architecture during these development and maturation stages related to changes in chromosome condensation, mitochondria aggregation and lipid droplet numbers.

Cyclin A2 modulates kinetochore-microtubule attachment in meiosis II.

Cyclin A2 is a crucial mitotic Cdk regulatory partner that coordinates entry into mitosis and is then destroyed in prometaphase within minutes of nuclear envelope breakdown. The role of cyclin A2 in female meiosis and its dynamics during the transition from meiosis I (MI) to meiosis II (MII) remain unclear. We found that cyclin A2 decreases in prometaphase I but recovers after the first meiotic division and persists, uniquely for metaphase, in MII-arrested oocytes. Conditional deletion of cyclin A2 from mouse oocytes has no discernible effect on MI but leads to disrupted MII spindles and increased merotelic attachments. On stimulation of exit from MII, there is a dramatic increase in lagging chromosomes and an inhibition of cytokinesis. These defects are associated with an increase in microtubule stability in MII spindles, suggesting that cyclin A2 mediates the fidelity of MII by maintaining microtubule dynamics during the rapid formation of the MII spindle.

Identification of an activation site in Bak and mitochondrial Bax triggered by antibodies.

During apoptosis, Bak and Bax are activated by BH3-only proteins binding to the α2-α5 hydrophobic groove; Bax is also activated via a rear pocket. Here we report that antibodies can directly activate Bak and mitochondrial Bax by binding to the α1-α2 loop. A monoclonal antibody (clone 7D10) binds close to α1 in non-activated Bak to induce conformational change, oligomerization, and cytochrome c release. Anti-FLAG antibodies also activate Bak containing a FLAG epitope close to α1. An antibody (clone 3C10) to the Bax α1-α2 loop activates mitochondrial Bax, but blocks translocation of cytosolic Bax. Tethers within Bak show that 7D10 binding directly extricates α1; a structural model of the 7D10 Fab bound to Bak reveals the formation of a cavity under α1. Our identification of the α1-α2 loop as an activation site in Bak paves the way to develop intrabodies or small molecules that directly and selectively regulate these proteins.

Loss of GGN leads to pre-implantation embryonic lethality and compromised male meiotic DNA double strand break repair in the mouse.

The integrity of male germ cell genome is critical for the correct progression of spermatogenesis, successful fertilization, and proper development of the offspring. Several DNA repair pathways exist in male germ cells. However, unlike somatic cells, key components of such pathways remain largely unidentified. Gametogenetin (GGN) is a testis-enriched protein that has been shown to bind to the DNA repair protein FANCL via yeast-two-hybrid assays. This finding and its testis-enriched expression pattern raise the possibility that GGN plays a role in DNA repair during spermatogenesis. Herein we demonstrated that the largest isoform GGN1 interacted with components of DNA repair machinery in the mouse testis. In addition to FANCL, GGN1 interacted with the critical component of the Fanconi Anemia (FA) pathway FANCD2 and a downstream component of the BRCA pathway, BRCC36. To define the physiological function of GGN, we generated a Ggn null mouse line. A complete loss of GGN resulted in embryonic lethality at the very earliest period of pre-implantation development, with no viable blastocysts observed. This finding was consistent with the observation that Ggn mRNA was also expressed in lower levels in the oocyte and pre-implantation embryos. Moreover, pachytene spermatocytes of the Ggn heterozygous knockout mice showed an increased incidence of unrepaired DNA double strand breaks (DSBs). Together, our results suggest that GGN plays a role in male meiotic DSB repair and is absolutely required for the survival of pre-implantation embryos.

DNA double strand breaks but not interstrand crosslinks prevent progress through meiosis in fully grown mouse oocytes.

There is some interest in how mammalian oocytes respond to different types of DNA damage because of the increasing expectation of fertility preservation in women undergoing chemotherapy. Double strand breaks (DSBs) induced by ionizing radiation and agents such as neocarzinostatin (NCS), and interstrand crosslinks (ICLs) induced by alkylating agents such as mitomycin C (MMC), are toxic DNA lesions that need to be repaired for cell survival. Here we examined the effects of NCS and MMC treatment on oocytes collected from antral follicles in mice, because potentially such oocytes are readily collected from ovaries and do not need to be in vitro grown to achieve meiotic competency. We found that oocytes were sensitive to NCS, such that this ionizing radiation mimetic blocked meiosis I and caused fragmented DNA. In contrast, MMC had no impact on the completion of either meiosis I or II, even at extremely high doses. However, oocytes treated with MMC did show γ-H2AX foci and following their in vitro maturation and parthenogenetic activation the development of the subsequent embryos was severely compromised. Addition of MMC to 1-cell embryos caused a similarly poor level of development, demonstrating oocytes have eventual sensitivity to this ICL-inducing agent but this does not occur during their meiotic division. In oocytes, the association of Fanconi Anemia protein, FANCD2, with sites of ICL lesions was not apparent until entry into the embryonic cell cycle. In conclusion, meiotic maturation of oocytes is sensitive to DSBs but not ICLs. The ability of oocytes to tolerate severe ICL damage and yet complete meiosis, means that this type of DNA lesion goes unrepaired in oocytes but impacts on subsequent embryo quality.

A global role for KLF1 in erythropoiesis revealed by ChIP-seq in primary erythroid cells.

KLF1 regulates a diverse suite of genes to direct erythroid cell differentiation from bipotent progenitors. To determine the local cis-regulatory contexts and transcription factor networks in which KLF1 operates, we performed KLF1 ChIP-seq in the mouse. We found at least 945 sites in the genome of E14.5 fetal liver erythroid cells which are occupied by endogenous KLF1. Many of these recovered sites reside in erythroid gene promoters such as Hbb-b1, but the majority are distant to any known gene. Our data suggests KLF1 directly regulates most aspects of terminal erythroid differentiation including production of alpha- and beta-globin protein chains, heme biosynthesis, coordination of proliferation and anti-apoptotic pathways, and construction of the red cell membrane and cytoskeleton by functioning primarily as a transcriptional activator. Additionally, we suggest new mechanisms for KLF1 cooperation with other transcription factors, in particular the erythroid transcription factor GATA1, to maintain homeostasis in the erythroid compartment.