BPA Exposure Affects Mouse Gastruloids Axial Elongation by Perturbing the Wnt/β-Catenin Pathway

Mammalian embryos are very vulnerable to environmental toxicants (ETs) exposure. Bisphenol A (BPA), one of the most diffused ETs, exerts endocrine-disrupting effects through estro-gen-mimicking and hormone-like properties, with detrimental health effects, including on reproduction. However, its impact during the peri-implantation stages is still unclear. This study, using gastruloids as a 3D stem cell-based in vitro model of embryonic development, showed that BPA exposure arrests their axial elongation when present during the Wnt/β-catenin pathway activation period by β-catenin protein reduction. Gastruloid reshaping might have been impeded by the downregulation of Snail, Slug and Twist, known to suppress E-cadherin expression and to activate the N-cadherin gene, and by the low expression of the N-cadherin protein. Also, the lack of gastruloids elongation might be related to altered exit of BPA-exposed cells from the pluripotency condition and their following differentiation. In conclusion, here we show that the inhibition of gastruloids' axial elongation by BPA might be the result of the concomitant Wnt/β-catenin perturbation, reduced N-cadherin expression and Oct4, T/Bra and Cdx2 altered patter expression, which all together concur in the impaired development of mouse gastruloids.

Extracellular vesicles secreted by cumulus cells contain microRNAs that are potential regulatory factors of mouse oocyte developmental competence

The role of cumulus cells (CCs) in the acquisition of oocyte developmental competence is not yet fully understood. In a previous study, we matured cumulus-denuded fully-grown mouse oocytes to metaphase II (MII) on a feeder layer of CCs (FL-CCs) isolated from developmentally competent (FL-SN-CCs) or incompetent (FL-NSN-CCs) SN (surrounded nucleolus) or NSN (not surrounding nucleolus) oocytes, respectively. We observed that oocytes cultured on the former could develop into blastocysts, while those matured on the latter arrested at the 2-cell stage. To investigate the CC factors contributing to oocyte developmental competence, here we focused on the CCs' release into the medium of extracellular vesicles (EVs) and on their miRNA content. We found that, during the 15-h transition to MII, both FL-SN-CCs and FL-NSN-CCs release EVs that can be detected, by confocal microscopy, inside the zona pellucida (ZP) or the ooplasm. The majority of EVs are <200 nm in size, which is compatible with their ability to cross the ZP. Next-generation sequencing of the miRNome of FL-SN-CC versus FL-NSN-CC EVs highlighted 74 differentially expressed miRNAs, with 43 up- and 31 down-regulated. Although most of these miRNAs do not have known roles in the ovary, in silico functional analysis showed that seven of these miRNAs regulate 71 target genes with specific roles in meiosis resumption (N = 24), follicle growth (N = 23), fertilization (N = 1), and the acquisition of oocyte developmental competence (N = 23). Overall, our results indicate CC EVs as emerging candidates of the CC-to-oocyte communication axis and uncover a group of miRNAs as potential regulatory factors.

Oocyte vitrification for fertility preservation is an evolving practice requiring a new mindset: societal, technical, clinical, and basic science-driven evolutions

Infertility is a condition with profound social implications. Indeed, it is not surprising that evolutions in both medicine and society affect the way in vitro fertilization is practiced. The keywords in modern medicine are the four principles, which implicitly involve a constant update of our knowledge and our technologies to fulfill the "prediction" and "personalization" tasks, and a continuous reshaping of our mindset in view of all relevant societal changes to fulfill the "prevention" and "participation" tasks. A worldwide aging population whose life priorities are changing requires that we invest in fertility education, spreading actionable information to allow women and men to make meaningful reproductive choices. Fertility preservation for both medical and nonmedical reasons is still very much overlooked in many countries worldwide, demanding a comprehensive update of our approach, starting from academia and in vitro fertilization laboratories, passing through medical offices, and reaching out to social media. Reproduction medicine should evolve from being a clinical practice to treat a condition to being a holistic approach to guarantee patients' reproductive health and well-being. Oocyte vitrification for fertility preservation is the perfect use case for this transition. This tool is acquiring a new identity to comply with novel indications and social needs, persisting technical challenges, brand-new clinical technologies, and novel revolutions coming from academia. This "views and reviews" piece aims at outlining the advancement of oocyte vitrification from all these tightly connected perspectives.

Unexpected silicon localization in calcium carbonate exoskeleton of cultured and fossil coccolithophores

Coccolithophores, marine calcifying phytoplankton, are important primary producers impacting the global carbon cycle at different timescales. Their biomineral structures, the calcite containing coccoliths, are among the most elaborate hard parts of any organism. Understanding the morphogenesis of coccoliths is not only relevant in the context of coccolithophore eco-physiology but will also inform biomineralization and crystal design research more generally. The recent discovery of a silicon (Si) requirement for crystal shaping in some coccolithophores has opened up a new avenue of biomineralization research. In order to develop a mechanistic understanding of the role of Si, the presence and localization of this chemical element in coccoliths needs to be known. Here, we document for the first time the uneven Si distribution in Helicosphaera carteri coccoliths through three synchrotron-based techniques employing X-ray Fluorescence and Infrared Spectromicroscopy. The enrichment of Si in specific areas of the coccoliths point to a targeted role of this element in the coccolith formation. Our findings mark a key step in biomineralization research because it opens the door for a detailed mechanistic understanding of the role Si plays in shaping coccolith crystals.

MALDI mass spectrometry imaging shows a gradual change in the proteome landscape during mouse ovarian folliculogenesis

Our knowledge regarding the role proteins play in the mutual relationship among oocytes, surrounding follicle cells, stroma, and the vascular network inside the ovary is still poor and obtaining insights into this context would significantly aid our understanding of folliculogenesis. Here, we describe a spatial proteomics approach to characterise the proteome of individual follicles at different growth stages in a whole prepubertal 25-day-old mouse ovary. A total of 401 proteins were identified by nano-scale liquid chromatography-electrospray ionisation-tandem mass spectrometry (nLC-ESI-MS/MS), 69 with a known function in ovary biology, as demonstrated by earlier proteomics studies. Enrichment analysis highlighted significant KEGG and Reactome pathways, with apoptosis, developmental biology, PI3K-Akt, epigenetic regulation of gene expression, and extracellular matrix organisation being well represented. Then, correlating these data with the spatial information provided by matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) on 276 follicles enabled the protein profiles of single follicle types to be mapped within their native context, highlighting 94 proteins that were detected throughout the secondary to the pre-ovulatory transition. Statistical analyses identified a group of 37 proteins that showed a gradual quantitative change during follicle differentiation, comprising 10 with a known role in follicle growth (NUMA1, TPM2), oocyte germinal vesicle-to-metaphase II transition (SFPQ, ACTBL, MARCS, NUCL), ovulation (GELS, CO1A2) and preimplantation development (TIF1B, KHDC3). The proteome landscape identified includes molecules of known function in the ovary, but also those whose specific role is emerging. Altogether, this work demonstrates the utility of performing spatial proteomics in the context of the ovary and offers sound bases for more in-depth investigations that aim to further unravel its spatial proteome.

Biomechanical forces and signals operating in the ovary during folliculogenesis and their dysregulation: implications for fertility

BACKGROUND

Folliculogenesis occurs in the highly dynamic environment of the ovary. Follicle cyclic recruitment, neo-angiogenesis, spatial displacement, follicle atresia and ovulation stand out as major events resulting from the interplay between mechanical forces and molecular signals. Morphological and functional changes to the growing follicle and to the surrounding tissue are required to produce oocytes capable of supporting preimplantation development to the blastocyst stage.

OBJECTIVE AND RATIONALE

This review will summarize the ovarian morphological and functional context that contributes to follicle recruitment, growth and ovulation, as well as to the acquisition of oocyte developmental competence. We will describe the changes occurring during folliculogenesis to the ovarian extracellular matrix (ECM) and to the vasculature, their influence on the mechanical properties of the ovarian tissue, and, in turn, their influence on the regulation of signal transduction. Also, we will outline how their dysregulation might be associated with pathologies such as polycystic ovary syndrome (PCOS), endometriosis or premature ovarian insufficiency (POI). Finally, for each of these three pathologies, we will highlight therapeutic strategies attempting to correct the altered biomechanical context in order to restore fertility.

SEARCH METHODS

For each area discussed, a systematic bibliographical search was performed, without temporal limits, using PubMed Central, Web of Science and Scopus search engines employing the keywords extracellular matrix, mechanobiology, biomechanics, vasculature, angiogenesis or signalling pathway in combination with: ovary, oogenesis, oocyte, folliculogenesis, ovarian follicle, theca, granulosa, cumulus, follicular fluid, corpus luteum, meiosis, oocyte developmental competence, preimplantation, polycystic ovary syndrome, premature ovarian insufficiency or endometriosis.

OUTCOMES

Through search engines queries, we yielded a total of 37 368 papers that were further selected based on our focus on mammals and, specifically, on rodents, bovine, equine, ovine, primates and human, and also were trimmed around each specific topic of the review. After the elimination of duplicates, this selection process resulted in 628 papers, of which 287 were cited in the manuscript. Among these, 89.2% were published in the past 22 years, while the remaining 8.0%, 2.4% or 0.3% were published during the 1990s, 1980s or before, respectively. During folliculogenesis, changes occur to the ovarian ECM composition and organization that, together with vasculature modelling around the growing follicle, are aimed to sustain its recruitment and growth, and the maturation of the enclosed oocyte. These events define the scenario in which mechanical forces are key to the regulation of cascades of molecular signals. Alterations to this context determine impaired folliculogenesis and decreased oocyte developmental potential, as observed in pathological conditions which are causes of infertility, such as PCOS, endometriosis or POI.

WIDER IMPLICATIONS

The knowledge of these mechanisms and the rules that govern them lay a sound basis to explain how follicles recruitment and growth are modulated, and stimulate insights to develop, in clinical practice, strategies to improve follicular recruitment and oocyte competence, particularly for pathologies like PCOS, endometriosis and POI.

Endocrine-Disrupting Chemicals, Gut Microbiota, and Human (In)Fertility-It Is Time to Consider the Triad

The gut microbiota (GM) is a complex and dynamic population of microorganisms living in the human gastrointestinal tract that play an important role in human health and diseases. Recent evidence suggests a strong direct or indirect correlation between GM and both male and female fertility: on the one hand, GM is involved in the regulation of sex hormone levels and in the preservation of the blood-testis barrier integrity; on the other hand, a dysbiotic GM is linked to the onset of pro-inflammatory conditions such as endometriosis or PCOS, which are often associated with infertility. Exposure to endocrine-disrupting chemicals (EDCs) is one of the main causes of GM dysbiosis, with important consequences to the host health and potential transgenerational effects. This perspective article aims to show that the negative effects of EDCs on reproduction are in part due to a dysbiotic GM. We will highlight (i) the link between GM and male and female fertility; (ii) the mechanisms of interaction between EDCs and GM; and (iii) the importance of the maternal-fetal GM axis for offspring growth and development.

Multi- and Transgenerational Effects of Environmental Toxicants on Mammalian Reproduction

Environmental toxicants (ETs) are an exogenous chemical group diffused in the environment that contaminate food, water, air and soil, and through the food chain, they bioaccumulate into the organisms. In mammals, the exposure to ETs can affect both male and female fertility and their reproductive health through complex alterations that impact both gametogeneses, among other processes. In humans, direct exposure to ETs concurs to the declining of fertility, and its transmission across generations has been recently proposed. However, multi- and transgenerational inheritances of ET reprotoxicity have only been demonstrated in animals. Here, we review recent studies performed on laboratory model animals investigating the effects of ETs, such as BPA, phthalates, pesticides and persistent contaminants, on the reproductive system transmitted through generations. This includes multigenerational effects, where exposure to the compounds cannot be excluded, and transgenerational effects in unexposed animals. Additionally, we report on epigenetic mechanisms, such as DNA methylation, histone tails and noncoding RNAs, which may play a mechanistic role in a nongenetic transmission of environmental information exposure through the germline across generations.

P-586 3D micro-Computed Tomography imaging and reconstruction of the mouse ovary before and after gonadotropins treatment

Study question

How does gonadotropins treatment impact on the number of the different follicle types, their 3D localization, and their recruitment and selection dynamics inside the ovary?

Summary answer

Treatment with gonadotropins modifies the dynamics of follicles recruitment and selection within the 3D context of the ovary.

What is known already

Gonadotropins regulate mouse folliculogenesis during follicles recruitment (type 4-5, T4-5) and selection for growth or elimination (T6-7). To further our understanding of the impact of gonadotropins treatment on folliculogenetic dynamics inside the ovary, we used Computed Tomography (CT).

3D imaging of the ovary provides information on its inner spatial organization, and microCT is the only technique that combines high resolution with cubic voxels and allows the organ 3D in-silico reconstruction. We recently published the method for microCT analysis of the adult mouse ovary demonstrating that follicle recruitment occurs simultaneously all-over the cortex, and folliculogenesis is completed within the same region.

Study design, size, duration

25-day-old CD1-mice were used since this age rightly precedes the first ovulation: follicles, from the primordial T1 to the pre-ovulatory T8, are all present, but corpora lutea (CL) are yet not formed. Ovaries from different individuals were analyzed by microCT: three not-treated controls (CTR); three injected with 3.5 I.U. PMSG and sacrificed 48hr later (PMSG); three treated first with PMSG, 48hr later injected with 3.5 I.U. hCG and then sacrificed after 15hr upon ovulation (PMSG+hCG).

Participants/materials, setting, methods

Ovaries were fixed in 4% Paraformaldehyde and treated with Lugol’s solution for 3hr at RT. Then, they were imaged with the EasyTom XL (RX Solutions) tomographic system, using a 1-1.2 µm/pixel resolution. Following microCT imaging, follicles classification (Fiji ImageJ, NIH), 3D mapping (XnConvert, XnSoft) and ovary in-silico reconstruction (Avizo-9, Thermo Fisher Scientific) were performed. ANOVA and Bonferroni post-hoc statistical analyses were done with RStudio &gt; (p &lt; 0.05).

Main results and the role of chance

Compared to CTR, 48hr after PMSG injection, the T3, T4 and T5 follicle classes remained numerically unchanged, suggesting that the FSH-dependent recruitment involving T4-5 follicles is balanced by an equivalent number of follicles growing from the preceding primordial pool. The most evident change in PMSG ovaries was a 5-fold decrease (p = 0.002) in the number of antral T7 follicles, at the stage of follicle selection. This observation was paralleled by the presence, in the medulla region, of many atretic-like follicles, characterized by a more intense microCT contrast associated with a collapsed antrum, de-structured granulosa-cell layers and fragmented oocytes.

In PMSG+hCG ovaries, the number of T3-7 follicles was analogous to that described for PMSG, although the atretic-like follicles almost disappeared, suggesting their elimination sometime prior to ovulation.

To understand whether follicle recruitment and selection have a territoriality within the 3D female gonad, ovaries were virtually divided into eight dorsal (D-I/II/III/IV) and ventral (V-I/II/III/IV) sectors. Compared to CTR, PMSG injection appeared to increase follicle selection in sectors V-I (p = 0.03), V-II (p = 0.01) and V-IV (p = 0.02), whereas PMSG+hCG displayed a higher follicle recruitment in sector V-IV (p = 0.0007). Overall, these data suggest a spatial differential effect of the gonadotropins treatment inside the 3D mouse ovary.

Limitations, reasons for caution

To strengthen the results and better account for the inter-individual variability in response to hormonal treatments, the number of ovaries/individuals should be increased. Also, important is extending the analysis to the time-interval after hCG injection, beyond 15 hr, to assess the effects of ovarian stimulation on subsequent cycles.

Wider implications of the findings

The method proposed allows to map all follicle stages and to reconstruct a 3D in-silico model of the mouse ovary. This approach could be extended to other Mammals, including human, in normal and pathological conditions, as well as in response to different hormonal stimuli (e.g., dose or type of gonadotropins).

Trial registration number

not applicable

Maternal effect factors that contribute to oocytes developmental competence: an update

Oocyte developmental competence is defined as the capacity of the female gamete to be fertilized and sustain development to the blastocyst stage. Epigenetic reprogramming, a correct cell division pattern, and an efficient DNA damage response are all critical events that, before embryonic genome activation, are governed by maternally inherited factors such as maternal-effect gene (MEG) products. Although these molecules are stored inside the oocyte until ovulation and exert their main role during fertilization and preimplantation development, some of them are already functioning during folliculogenesis and oocyte meiosis resumption. This mini review summarizes the crucial roles played by MEGs during oocyte maturation, fertilization, and preimplantation development with a direct/indirect effect on the acquisition or maintenance of oocyte competence. Our aim is to inspire future research on a topic with potential clinical perspectives for the prediction and treatment of female infertility.

Functional and structural phenotyping of cardiomyocytes in the 3D organization of embryoid bodies exposed to arsenic trioxide

Chronic exposure to environmental pollutants threatens human health. Arsenic, a world-wide diffused toxicant, is associated to cardiac pathology in the adult and to congenital heart defects in the foetus. Poorly known are its effects on perinatal cardiomyocytes. Here, bioinformatic image-analysis tools were coupled with cellular and molecular analyses to obtain functional and structural quantitative metrics of the impairment induced by 0.1, 0.5 or 1.0 µM arsenic trioxide exposure on the perinatal-like cardiomyocyte component of mouse embryoid bodies, within their 3D complex cell organization. With this approach, we quantified alterations to the (a) beating activity; (b) sarcomere organization (texture, edge, repetitiveness, height and width of the Z bands); (c) cardiomyocyte size and shape; (d) volume occupied by cardiomyocytes within the EBs. Sarcomere organization and cell morphology impairment are paralleled by differential expression of sarcomeric α-actin and Tropomyosin proteins and of acta2, myh6 and myh7 genes. Also, significant increase of Cx40, Cx43 and Cx45 connexin genes and of Cx43 protein expression profiles is paralleled by large Cx43 immunofluorescence signals. These results provide new insights into the role of arsenic in impairing cytoskeletal components of perinatal-like cardiomyocytes which, in turn, affect cell size, shape and beating capacity.

O-157 Micro-Computed Tomography of the adult mouse ovary: an in-silico 3D reconstruction of folliculogenesis

Study question

Which are the spatial dynamics of follicles recruitment and growth inside the ovary?

Summary answer

3D micro-Computed Tomography (microCT) shows a simultaneous and homogeneous distribution of follicle recruitment all-over the cortex,and subsequent growth within the same ovarian region.

What is known already

In the mouse ovary, folliculogenesis progresses from the primordial type 1 (T1) to the fully-grown T8 follicle. Most of our knowledge of the folliculogenetic process has been obtained by disaggregating the ovary into its functional units (i.e., follicles and oocytes), thus losing the complexity of the whole histo-functional context.

To date, few studies employed 3D imaging approaches to gain information on the inside 3D ovary organisation. MicroCT is the only technique that combines a high spatial resolution (down to ∼1 µm) with the production of a true 3D organ reconstruction, with cubic voxels and isotropic resolution. 

Study design, size, duration

Three ovaries of three different adult mice were treated with the contrast agent and then imaged with microCT. A typical experiment required a total of 35 man/h from ovaries isolation to completion of X-ray scanning, and 24 man/h for follicles classification and mapping.

Participants/materials, setting, methods

Three ovaries of three different 8-week-old CD1 mice were fixed in 4% Paraformaldehyde and treated with Lugol’s solution for 3 hr at RT. Ovaries were scanned with Skyscan 1172 (Bruker) using a 1.5 µm/pixel resolution. MicroCT sections were processed with Fiji ImageJ (NIH), and 3D rendering of follicles and blood vessels were obtained with Avizo-9 (Thermo Fisher Scientific). ANOVA and Bonferroni post-­hocstatistical analyses were performed with RStudio, considering data significantly different when p &lt; 0.05.

Main results and the role of chance

Using microCT we built the first in silico3D reconstruction of the tiny mouse ovary, identifying, mapping and counting follicles,from pre-antral secondary T4 (53.2 + 12.7 µm in diameter) to fully-grown antral T8 (321.0 + 21.3 µm), and the corpora lutea.MicroCTbrought up the main functional compartments of the growing follicle, i.e., granulosa and cumulus cells, the antrum, the zona pellucida, and the oocyte with its nucleus. Instead, primordial and primary follicles (T1–T3) could not be observed, perhaps due to the reduced size of their enclosed oocyte and to the absence of a well-formed zona pellucida around the germ cell. In addition, our analysis allowed the visualisation and 3D modelling of the main ovarian vasculature, from the largest vessel that enters the organ at the hilum site (∼150 µm size in diameter)to smaller branches present in the medulla region (∼35 µm).

These results show that each of the eight ovarian sectors, virtually segmented along the dorsal-ventral axis,houses an equal number of each follicle type, suggesting a simultaneous and homogeneous distribution of follicle recruitment all-over the cortex,and subsequent growth within the same ovarian region.

Limitations, reasons for caution

To strengthen the results, the number of ovaries/individuals analysed should be increased.

Wider implications of the findings

This 3D mapping of follicles and vessels could contribute our understanding of folliculogenesis dynamics, not only under normal conditions, but also during ageing, after hormones or drugs administration, or in the presence of ovarian pathologies. 

Trial registration number

not applicable

Three-dimensional imaging and reconstruction of the whole ovary and testis: a new frontier for the reproductive scientist

The 3D functional reconstruction of a whole organ or organism down to the single cell level and to the subcellular components and molecules is a major future scientific challenge. The recent convergence of advanced imaging techniques with an impressively increased computing power allowed early attempts to translate and combine 2D images and functional data to obtain in-silico organ 3D models. This review first describes the experimental pipeline required for organ 3D reconstruction: from the collection of 2D serial images obtained with light, confocal, light-sheet microscopy or tomography, followed by their registration, segmentation and subsequent 3D rendering. Then, we summarise the results of investigations performed so far by applying these 3D image analyses to the study of the female and male mammalian gonads. These studies highlight the importance of working towards a 3D in-silico model of the ovary and testis as a tool to gain insights into their biology during the phases of differentiation or adulthood, in normal or pathological conditions. Furthermore, the use of 3D imaging approaches opens to key technical improvements, ranging from image acquisition to optimisation and development of new processing tools, and unfolds novel possibilities for multidisciplinary research.

Cytoplasmic movements of the early human embryo: imaging and artificial intelligence to predict blastocyst development

RESEARCH QUESTION

Can artificial intelligence and advanced image analysis extract and harness novel information derived from cytoplasmic movements of the early human embryo to predict development to blastocyst?

DESIGN

In a proof-of-principle study, 230 human preimplantation embryos were retrospectively assessed using an artificial neural network. After intracytoplasmic sperm injection, embryos underwent time-lapse monitoring for 44 h. For comparison, standard embryo assessment of each embryo by a single embryologist was carried out to predict development to blastocyst stage based on a single picture frame taken at 42 h of development. In the experimental approach, in embryos that developed to blastocyst or destined to arrest, cytoplasm movement velocity was recorded by time-lapse monitoring during the first 44 h of culture and analysed with a Particle Image Velocimetry algorithm to extract quantitative information. Three main artificial intelligence approaches, the k-Nearest Neighbour, the Long-Short Term Memory Neural Network and the hybrid ensemble classifier were used to classify the embryos.

RESULTS

Blind operator assessment classified each embryo in terms of ability to develop to blastocyst, with 75.4% accuracy, 76.5% sensitivity, 74.3% specificity, 74.3% precision and 75.4% F1 score. Integration of results from artificial intelligence models with the blind operator classification, resulted in 82.6% accuracy, 79.4% sensitivity, 85.7% specificity, 84.4% precision and 81.8% F1 score.

CONCLUSIONS

The present study suggests the possibility of predicting human blastocyst development at early cleavage stages by detection of cytoplasm movement velocity and artificial intelligence analysis. This indicates the importance of the dynamics of the cytoplasm as a novel and valuable source of data to assess embryo viability.

Three-Dimensional Micro-Computed Tomography of the Adult Mouse Ovary

In the mouse ovary, folliculogenesis proceeds through eight main growth stages, from small primordial type 1 (T1) to fully grown antral T8 follicles. Most of our understanding of this process was obtained with approaches that disrupted the ovary three-dimensional (3D) integrity. Micro-Computed Tomography (microCT) allows the maintenance of the organ structure and a true in-silico 3D reconstruction, with cubic voxels and isotropic resolution, giving a precise spatial mapping of its functional units. Here, we developed a robust method that, by combining an optimized contrast procedure with microCT imaging of the tiny adult mouse ovary, allowed 3D mapping and counting of follicles, from pre-antral secondary T4 (53.2 ± 12.7 μm in diameter) to antral T8 (321.0 ± 21.3 μm) and corpora lutea, together with the major vasculature branches. Primordial and primary follicles (T1–T3) could not be observed. Our procedure highlighted, with unprecedent details, the main functional compartments of the growing follicle: granulosa, antrum, cumulus cells, zona pellucida, and oocyte with its nucleus. The results describe a homogeneous distribution of all follicle types between the ovary dorsal and ventral regions. Also, they show that each of the eight sectors, virtually segmented along the dorsal-ventral axis, houses an equal number of each follicle type. Altogether, these data suggest that follicle recruitment is homogeneously distributed all-over the ovarian surface. This topographic reconstruction builds sound bases for modeling follicles position and, prospectively, could contribute to our understanding of folliculogenesis dynamics, not only under normal conditions, but, importantly, during aging, in the presence of pathologies or after hormones or drugs administration.

Sertoli-immature spermatids disengagement during testis regression in the armadillo

In nature, mammalian seasonal breeders undergo spermatogenetic arrest during the non-breeding season. In the large hairy armadillo Chaetophractus villosus, testis regression initiates with immature post-meiotic germ cells sloughing into the tubule lumen and continues with the death of the remaining spermatocytes. At the end of the regression period, only spermatogonia and Sertoli cells persist in the seminiferous epithelium. It has been suggested that cell sloughing is determined by changes in the adhesion complexes between Sertoli cells and spermatids, which are mediated by low intra-testicular testosterone levels. By immunofluorescence and Western blotting we studied key proteins of the N-cadherin/N-cadherin and A6B1-integrin/laminin interlocks that contribute to the complex Sertoli/spermatid adhesion system throughout the eight stages of the seminiferous epithelium cycle in the comparison between active and regressing testes. In active testis, B1-integrin, laminin G3, N-cadherin, B-catenin, P-B-catenin-Tyr654, FAK, P-FAK-Tyr397, SRC, P-SRC-Tyr416 proteins present a spermatogenetic cycle-dependent localisation pattern, unmaintained in regressing testes. In the latter, quantitative variations and changes in the phosphorylation state of protein FAK, SRC and B-catenin contribute to the disassembly of the N-cadherin/N-cadherin and A6B1-integrin/laminin interlocks, thus promoting the massive release of immature spermatids.

In Vitro Maturation of Fully Grown Mouse Antral Follicles in the Presence of 1 nM 2-Hydroxyestradiol Improves Oocytes' Developmental Competence

Cathecolestrogens are estradiol metabolites produced during folliculogenesis in the mammalian ovary. 2-Hydroxyestradiol (2-OHE₂) is one of the most abundant although its role remains unknown. The aim of this study is to investigate whether the presence of 2-OHE₂ during the germinal vesicle-to-metaphase II transition affects oocyte meiotic and preimplantation developmental competence. Mouse cumulus-oocyte complexes (COCs), isolated from fully grown antral follicles, were in vitro–matured (IVM) in the presence of 2-OHE₂ (0.1, 1, 10 or 100 nM) for 6 or 15 h; then, their meiotic and developmental competence was evaluated using a number of cytological quality markers. With the exception of the highest dose (100 nM), the addition of 2-OHE₂ to the IVM medium, did not alter, compared with untreated control, the frequency of oocytes that reached the MII stage. Instead, IVM in the presence of 1 nM 2-OHE₂ highly increased the rate of preimplantation development and blastocyst quality. To understand whether this positive effect could be attributed to the events occurring during meiosis resumption, we analysed a number of specific cytological quality markers of the asymmetric division, such as PB-I volume and position, presence and extension of the cortical F-actin cap, meiotic spindle shape and area, and microtubule organisation centre localisation. The results highlighted how the presence of 1 nM 2-OHE₂ significantly improved the overall cytological organisation required for a correct asymmetric division. Our results contribute a first step to acknowledge a potential role of this estradiol metabolite during the GV-to-MII transition, contributing to the acquisition of oocytes developmental competence.

X-Chromosome Inactivation during Preimplantation Development and in Pluripotent Stem Cells

X dosage compensation between XX female and XY male mammalian cells is achieved by a process known as X-chromosome inactivation (XCI). XCI initiates early during preimplantation development in female cells, and it is subsequently stably maintained in somatic cells. However, XCI is a reversible process that occurs in vivo in the inner cell mass of the blastocyst, in primordial germ cells or in spermatids during reprogramming. Erasure of transcriptional gene silencing can occur though a mechanism named X-chromosome reactivation (XCR). XCI and XCR have been substantially deciphered in the mouse, whereas they still remain debated in the human. In this review, we summarized the recent advances in the knowledge of X-linked gene dosage compensation during mouse and human preimplantation development and in pluripotent stem cells.

A Brief Incubation of Cumulus-Enclosed Mouse Eggs in a Calcium-Free Medium Containing a High Concentration of Calcium-Chelator Markedly Improves Preimplantation Development

The presence of cumulus cells (CCs) surrounding ovulated eggs is beneficial to in vitro fertilization and preimplantation development outcomes in several mammalian species. In the mouse, this contribution has a negligible effect on the fertilization rate; however, it is not yet clear whether it has positive effects on preimplantation development. Here, we compared the rates of in vitro fertilization and preimplantation development of ovulated B6C3F1 CC-enclosed vs. CC-free eggs, the latter obtained either after a 5 min treatment in M2 medium containing hyaluronidase or after 5-25 min in M2 medium supplemented with 34.2 mM EDTA (M2-EDTA). We found that, although the maintenance of CCs around ovulated eggs does not increment their developmental rate to blastocyst, the quality of the latter is significantly enhanced. Most importantly, for the first time, we describe a further quantitative and qualitative improvement, on preimplantation development, when CC-enclosed eggs are isolated from the oviducts in M2-EDTA and left in this medium for a total of 5 min prior to sperm insemination. Altogether, our results establish an important advancement in mouse IVF procedures that would be now interesting to test on other mammalian species.

Chronic cypermethrin exposure alters mouse embryonic stem cell growth kinetics, induces Phase II detoxification response and affects pluripotency and differentiation gene expression

Worldwide uncontrolled use of synthetic pyrethroids contaminates water and soil leading to health hazards. Cypermethrin (CYP), the most used pyrethroid, induces detrimental effects on adults and embryos at different stages of development of several vertebrate species. In Mammals, CYP-induced alterations have been previously described in adult somatic cells and in post-implantation embryos. It remains unknown whether CYP has effects during pre-implantation development. Studies to access pre-implantation embryo toxicity are complicated by the restricted number of blastocysts that may be obtained, either in vivo or in vitro. Embryonic stem cells (ESCs) are an in vitro model study that overcomes these limitations, as millions of pluripotent cells are available to the analysis. Also, ESCs maintain the same pluripotency characteristics and differentiation capacity of the inner cell mass (ICM) present in the blastocyst, from which they derive. In this work, using mouse R1 ESCs, we studied CYP-induced cell death, ROS production, the activation of oxidative stress-related and detoxification responses and the population growth kinetics following 72 h exposure at the 0.3 mM LD50 dose. Also, the expression levels of pluripotency genes in exposed ESCs and of markers of the three germ layers after their differentiation into embryoid bodies (EBs) were determined. Two apoptotic waves were observed at 12-24 h and at 72 h. The increase of ROS production, at 24 h until the end of the culture period, was accompanied by the induction, at 48 h, of redox-related Cat, Sod1, Sod2, Gpx1 and Gpx4 genes. Up-regulation of Cyp1b1, but not of Cyp1a1, phase I gene was detected at 72 h and induction of Nqo1, Gsta1 and Ugt1a6 phase II genes began at 24 h exposure. The results show that exposed R1 ESCs activate oxidative stress-related and detoxification responses, although not sufficient, during the culture period tested, to warrant recovery of the growth rate observed in untreated cells. Also, CYP exposure altered the expression of Oct-4 and Nanog pluripotency genes in ESCs and, when differentiated into EBs, the expression of Fgf5, Brachyury and Foxa2, early markers of the ectoderm, mesoderm and endoderm germ layers, respectively. NIH/3T3 cells, a differentiated cell line of embryonic origin, were used for comparison.

Chromatin organization and timing of polar body I extrusion identify developmentally competent mouse oocytes

In the mouse, the use of the DNA-binding fluorochrome Hoechst 33342 allows the classification of fully-grown antral oocytes into two categories distinguished by their chromatin conformation: surrounding nucleolus (SN) and not-surrounding nucleolus (NSN) oocytes, the former capable of completing development, the latter unable to proceed beyond the 2-cell stage. In the present study, time-lapse observation of SN and NSN oocyte GV-to-MII transition highlighted differences in the timing of germinal vesicle breakdown (GVBD) and polar body I (PB-I) extrusion. PB-I extrusion, but not GVBD, revealed the presence of three main groups of significantly different oocytes: Group A (456-576 min) comprising mainly SN oocytes (91.4%), group B (584-728 min) entailing an almost equivalent percentage of SN (52.7%) and NSN (47.3%) oocytes, whereas group C (736-896 min) consisting of almost all NSN (94.4%) oocytes. In a further set of time-lapse experiments, GV oocytes were in vitro matured without Hoechst staining and, depending on the timing of PB-I extrusion, sorted into group A, B or C, inseminated with sperm and observed throughout preimplantation. The results show that 26.2 ± 12.3% of group A, 2.4 ± 5.0% of group B and none of group C MII oocytes developed to blastocyst. Overall, this study shows that SN oocytes that complete MI earlier are those with a better developmental competence. The possibility to avoid the use of the invasive DNA-binding fluorochrome Hoechst is relevant for future applications in human and domestic animal reproductive technologies.