Distribution and content of lipid droplets and mitochondria in pig parthenogenetically activated embryos after delipation

Agarose-based 3D culture improved the developmental competence of oocyte-granulosa complex isolated from porcine preantral follicle

Various models have been established to culture whole follicles of the Preantral stage; however, the process remains inefficient and is an ongoing challenge formation. It is reported that oocyte-cumulus-granulosa complexes (OCGCs) isolated from Early Antral follicles (EAFs) undergo in vitro growth (IVG) and acquire meiotic competence in some animals. However, IVG for the oocyte-granulosa complexes (OGCs) from Preantral Follicles (PAFs) has not been firmly established. The present study indicated that the use of a modified medium with Ascorbic Acid (50 μM) facilitated granulosa cell proliferation, promoted cumulus cell differentiations, and increased antrum formation for the OGCs isolated from PAFs (0.3-0.4 mm). However, the two-dimensional 96-well plate system (2D) experienced smaller size follicles and could not prolong more than 10 days of IVG. Another method is to use an Agarose matrix 3D system to provide a soft, non-adhesive base that supports the IVG of OGCs isolated from PAFs and promotes cell proliferation, antrum formation, and maintenance for 14 days. OGCs that were grown using this method retained their spherical morphology, which in turn helped to attain healthy granulosa cells and maintain their connection with oocytes, in addition, these oocytes significantly increased diameter and lipid content, indicating developmental competence. Our result indicated that the OGCs from PAFs after IVG undergo a change in chromatin morphology and expression of acetylation of histone H3 at lysine 9 (Ac-H3-K9) and methylation of histone H3 at lysine 4 (Me-H3-K4), similar to the in vivo oocytes isolated from the ovary. Likewise, IVG oocytes cultured for maturation showed full cumulus expansion and reached mature oocytes. Furthermore, after in vitro maturation, IVG oocytes underwent the first cleavage following parthenogenetic activation. In conclusion, while most studies used whole follicles from the Preantral stage for IVG, our research finding was the first to reveal that oocytes isolated from the final stage of PAFs can migrate out of the follicle and undergo IVG under suitable conditions.

Characterization of multitype colonies originating from porcine blastocysts produced in vitro

Many types of embryonic stem cells have been induced from pre-implantation blastocysts to study the specification of early lineages. Various cell lines have been established using chemicals, including excessive inhibitory molecules. Previous studies have also aimed to purify cell populations representing a single embryonic lineage from a protocol. In this study, we used a novel culture condition to induce cells from blastocyst seeding and analyzed their characteristics. Next, signaling inhibitors were introduced during the cell culture period. Furthermore, we investigated the cell types using RNA sequencing. Each type of cell population showed a distinct morphology and reactivity with alkaline phosphatase. Marker proteins enabled each cell type to be distinguished by immunocytochemistry, and genes such as Sox17, Gata4, Gata6, T, and Cdx2 showed applicability for the discrimination of cell types. Signaling inhibitors suppressed the production of some cell types, and gene expression and marker protein patterns were collapsed. RNA-sequencing suggested cell-type-specific marker genes and the correlation among samples. In conclusion, four types of cells could be induced from porcine embryos using a single protocol, and they could be isolated manually. Our data will help promote the study of lineage segregation based on embryonic cells.

Ramelteon Reduces Oxidative Stress by Maintenance of Lipid Homeostasis in Porcine Oocytes

This study aimed to determine the underlying mechanism of ramelteon on the competence of oocyte and subsequent embryo development in pigs during in vitro maturation (IVM). Our results showed that the cumulus expansion index was significantly lower in the control group compared to the ramelteon groups (p < 0.05). Moreover, supplementation of 10−11 and 10−9 M ramelteon significantly increased the cumulus expansion and development-related genes expression, and reduced apoptosis in cumulus cells (p < 0.05). In oocytes, the nuclear maturation rate was significantly improved in 10−11, 10−9, and 10−7 M ramelteon groups compared to the control (p < 0.05). Additionally, the level of intracellular GSH was significantly increased and ROS was significantly decreased in ramelteon-supplemented groups, and the gene expression of oocyte development and apoptosis were significantly up- and down-regulated by 10−11 and 10−9 M ramelteon (p < 0.05), respectively. The immunofluorescence results showed that the protein levels of GDF9, BMP15, SOD1, CDK1, and PGC1α were significantly increased by 10−11 M ramelteon compared to the control (p < 0.05). Although there was no significant difference in cleavage rate, the blastocyst formation rate, total cell numbers, and hatching/-ed rate were significantly improved in 10−11 M ramelteon group compared to the control (p < 0.05). Furthermore, embryo development, hatching, and mitochondrial biogenesis-related genes were dramatically up-regulated by 10−11 M ramelteon (p < 0.05). In addition, the activities of lipogenesis and lipolysis in oocytes were dramatically increased by 10−11 M ramelteon compared to the control (p < 0.05). In conclusion, supplementation of 10−11 M ramelteon during IVM improved the oocyte maturation and subsequent embryo development by reducing oxidative stress and maintenance of lipid homeostasis.

Genes regulating hormone stimulus and response to protein signaling revealed differential expression pattern during porcine oocyte in vitro maturation, confirmed by lipid concentration

Genes influencing oocyte maturation may be valuable for predicting their developmental potential, as well as discerning the mechanistic pathways regulating oocyte development. In the presented research microarray gene expression analysis of immature and in vitro matured porcine oocytes was performed. Two groups of oocytes were compared in the study: before (3 × n = 50) and after in vitro maturation (3 × n = 50). The selection of viable oocytes was performed using the brilliant cresyl blue (BCB) test. Furthermore, microarrays and RT-qPCR was used to analyze the transcriptome of the oocytes before and after IVM. The study focused on the genes undergoing differential expression in two gene-ontology groups: “Cellular response to hormone stimulus” and “Cellular response to unfolded protein”, which contain genes that may directly or indirectly be involved in signal transduction during oocyte maturation. Examination of all the genes of interest showed a lower level of their expression after IVM. From the total number of genes in these gene ontologies ten of the highest change in expression were identified: FOS, ID2, BTG2, CYR61, ESR1, AR, TACR3, CCND2, EGR2 and TGFBR3. The successful maturation of the oocytes was additionally confirmed with the use of lipid droplet assay. The genes were briefly described and related to the literature sources, to investigate their potential roles in the process of oocyte maturation. The results of the study may serve as a basic molecular reference for further research aimed at improving the methods of oocyte in vitro maturation, which plays an important role in the procedures of assisted reproduction.

Effect of cryopreservation on the ability of granulosa cells to support in vitro development of oocytes derived from porcine early antral follicles

Granulosa cells (GCs) contribute to oocyte development. The present study addressed the effect of cryopreservation on the ability of GCs to support oocyte development. GCs were collected from antral follicles. Oocyte granulosa cell complexes (OGCs) derived from early antral follicles were cultured with additional fresh-GCs or frozen-thawed-GCs for 14 days, and the developmental ability and characteristics of the oocytes grown in vitro were examined. Furthermore, fresh- or frozen-thawed-GCs were cultured for two days, and the effects of cryopreservation on the characteristics of GCs were examined. The developmental ability of blastocysts and the acetylation levels of H4K12 in oocytes grown in vitro did not significantly differ among the three culture conditions: OGCs cultured with additional fresh-GCs, frozen-thawed-GCs, or without additional GCs. Although both fresh- and frozen-thawed-GCs exhibited increased ATP content compared with that in oocytes developed without additional GCs, only fresh-GCs showed significantly increased lipid content in oocytes grown in vitro. ATP content, reactive oxygen content, mitochondrial membrane potential, and mitochondrial DNA copy number were greater in cultured frozen-thawed-GCs compared with fresh-GCs. In contrast, lipid content of cultured frozen-thawed-GCs was lower than that of fresh-GCs. Both fresh- and frozen-GCs support oocyte growth, but cryopreservation changes the properties of GCs in a manner that affects the energy status of oocytes grown in vitro.

Follicular factors determining the developmental competence of porcine oocyte

PURPOSE

This study aimed to examine the relationship between granulosa cells (GCs), number of follicles, and the ability of follicular fluid to support in vitro growth of oocytes.

METHODS

The culture medium was supplemented with follicular fluid (FF) collected from GC-rich ovaries and GC-poor ovaries, and its effect on in vitro growth and quality of oocytes derived from early antral follicles (EAFs) was assessed.

RESULTS

GC-rich FF treatment enhanced oocyte growth and augmented changes in the chromatin configuration and lipid content of oocytes when compared to oocytes treated with GC-poor FF. Moreover, oocytes treated with GC-rich FF had a higher ability to progress to the blastocyst stage, than oocytes derived from large antral follicles (3-5 mm in diameter). In addition, supplementation of the culture medium with either GC-rich or GC-poor FF enhanced histone acetylation in oocytes grown in vitro.

CONCLUSION

GC-rich FF contains key factors that support in vitro oocyte growth; hence, oocytes grown in GC-rich FF medium had high developmental competence, which was comparative to the oocytes grown in vivo.

The consequences of porcine IVM medium supplementation with follicular fluid become reflected in embryo quality, yield and gene expression patterns

Oocyte and embryo developmental competence are shaped by multiple extrinsic and intrinsic factors. One of the most extensive research areas in the last decade is the regulation of lipid metabolism in oocytes and embryos of different species. We hypothesized that differences in developmental competence of oocytes and embryos between prepubertal and cyclic gilts may arise due to distinct fatty acid profiles in follicular fluid. We found that supplementation of oocyte maturation media with follicular fluid from prepubertal pigs affected quality and development of embryos from prepubertal pigs while embryos of cyclic pigs were not affected. PLIN2, SCD and ACACA transcripts involved in lipid metabolism were upregulated in embryos originating from oocytes of prepubertal pigs matured with autologous follicular fluid. The surface occupied by lipid droplets tend to increase in oocytes matured with follicular fluid from prepubertal pigs regardless oocyte origin. The change into follicular fluid of cyclic pigs increased the efficiency of embryo culture and improved quality, while gene expression was similar to embryos obtained from cyclic gilts. We assume that the follicular fluids of prepubertal and cyclic pigs influenced the quality of oocytes and embryos obtained from prepubertal pigs which are more susceptible to suboptimal in vitro culture conditions.

Apoptosis and developmental capacity of vitrified parthenogenetic pig blastocysts

This study was conducted to evaluate whether the poor developmental capacity of pig embryos after vitrification was related to the occurrence of apoptosis. Parthenogenetic blastocysts were used as the research material. The blastocoel recovery rate, mitochondrial membrane potential (ΔΨm), amount of early apoptosis, activities of several caspases, and relative abundance of mRNA of apoptosis-related genes involved in mitochondria and death receptor apoptotic pathways were detected before or after vitrification. The results indicate that the blastocoel recovery rate (31.0%) and total cells (31.8) of vitrified blastocysts were less than those of fresh blastocysts (100% and 38.2, P <  0.05). The ΔΨm of vitrified blastocysts was 0.46, which was less than that of fresh blastocysts (1.02, P <  0.05). The rate of apoptotic cells in vitrified blastocysts (8.1%) after TUNEL (TdT-mediated dUTP Nick-End Labeling) assay was markedly greater than that in fresh blastocysts (3.9%, P <  0.05). The pan-caspase, caspase-3, caspase-8 and caspase-9 activities of vitrified blastocysts (20.7, 20.6, 17.6 and 19.9) were markedly greater than those of fresh blastocysts (7.4, 6.5, 5.5 and 6.3, P <  0.05). The real-time PCR results indicated that relative abundance of caspase-8 and TNF-α mRNA from death receptor apoptotic pathway and caspase-9 for the mitochondrial apoptotic pathway genes in the vitrified group were greater than those in the fresh group P <  0.05). The relative abundance of Bcl-2 and SOD-1 mRNA for the mitochondrial pathway genes in the vitrified group was less than those in the fresh group (P <  0.05). In conclusion, the poor developmental capacity of vitrified parthenogenetic pig blastocysts was closely related with apoptosis. Both mitochondria and death receptor-mediated apoptotic pathways participated the occurrence of this apoptosis.

Follicular factors determining granulosa cell number and developmental competence of porcine oocytes

PURPOSE

Granulosa cell (GC) number in follicles is a simple characteristic of follicles. The present study examined the hypothesis that follicular fluid (FF) determines GC number and oocyte developmental ability and revealed the molecular background determining the number of follicular GCs.

METHODS

FF was collected from antral follicles (3-5 mm in diameter), after which the number of GCs per follicle was determined for each donor gilt using real time PCR targeting single copy gene. GCs were analyzed by next-generation RNA sequencing and IPA pathway analysis.

RESULTS

When oocyte cumulus cell-oocyte-complexes (COCs) were cultured in maturation medium containing 10% of each individual FF, the rate of development to the blastocyst stage was significantly correlated with the number of GCs in the donor gilt. In addition, when GCs were cultured in medium containing FF, the proliferative activity of the GCs was also significantly correlated to the number of GCs in the donor gilt. Moreover, when the FFs were categorized based on the number of GCs in the follicle, it was found that supplementation of culture media with GC-rich FF improved the developmental ability of oocytes compared to those supplemented with GC-poor FF. RNA sequencing and a pathway analysis of GCs from GC-rich and -poor follicles revealed the key regulatory pathway determining GC number in follicles.

CONCLUSION

GC number may be a useful marker for "good" follicles and oocytes, and the characteristics of the FFs determine granulosa cell number and oocyte developmental ability.

Glycine treatment enhances developmental potential of porcine oocytes and early embryos by inhibiting apoptosis

Glycine, a component of glutathione (GSH), plays an important role in protection from reactive oxygen species (ROS) and inhibition of apoptosis. The aim of this study was to determine the effect of glycine on in vitro maturation (IVM) of porcine oocytes and their developmental competence after parthenogenetic activation (PA). We examined nuclear maturation, ROS levels, apoptosis, mitochondrial membrane potential (ΔΨm), and ATP concentration, as well as the expression of several genes related to oocyte maturation and development. Our studies found that treatment with glycine in IVM culture medium increased nuclear maturation rate, but varying the concentrations of glycine (0.6, 6, or 12 mM) had no significant effect. Furthermore, 6 mM glycine supported greater blastocyst formation rates and lesser apoptosis after PA than the other concentrations (P < 0.05). All the glycine treatment groups had decreased levels of ROS in both matured oocytes and at the 2-cell stage (P < 0.05). At the 2-cell stage, the 6 mM glycine group had ROS levels that were lesser than the other 2 glycine treatment groups (0.6 and 12 mM). From this, we deemed 6 mM to be the optimal condition, and we then investigated the effects of 6 mM glycine on gene expression. The expression of both FGFR2 and Hsf1 were greater than the control group in mature oocytes. The glycine treatment group had greater levels of expression of an antiapoptotic gene (Bcl2) in mature oocytes and cumulus cells and lesser levels of expression of a proapoptotic gene (Bax) in PA blastocysts (P < 0.05). In addition, mitochondrial ΔΨm and ATP concentration were increased in 6 mM glycine group compared with the control group. In conclusion, our results suggest that glycine plays an important role in oocyte maturation and later development by reducing ROS levels and increasing mitochondrial function to reduce apoptosis.

The influence of delipidation on triglyceride and LIPIN1 of porcine embryos derived from parthenogenetic activation

Proteins in the LIPIN family play key roles in lipid synthesis mainly on triacylglycerol (TAG) biosynthesis, and they also act as transcriptional coactivators to regulate the expression of genes involved in lipid metabolism with other nuclear factors. Hence, this study was designed to investigate LIPIN1 in pig oocytes and embryos by the delipidation. After delipidation, the content of lipids (LDs) and TAG in MII oocyte was significantly reduced; however, a similar increasing tendency of TAG was shown during embryos development. Subsequently, the expression of genes related to TAG biosynthesis including GPAT1, AGPAT1, AGPAT2, LIPIN1, DGAT and the nuclear factors interacted with LIPIN1 including PPARα and PPARγ was investigated. It is obvious that DGAT and GPAT1, and LIPIN1 increased significantly after delipidation at 1-cell and 4-cell stage, and the expression of PPARα and PPARγ also increased at 4-cell stage. By immunofluorescence staining and Western blots, LIPIN1 was found to exhibit a dynamic localization pattern and gradually increase with the development of delipated embryo. In the early developmental stages (1-, 2- and 4-cell stages), it was distributed over the cortical layer. But at the blastocyst stage, a homogeneous distribution of LIPIN1 was observed in cytoplasm. At 2-cell stage, the expression of PPARα decreased when LIPIN1 was interfered by small interfering RNA, but PPARγ has no significant difference. Therefore, in this study, we find after delipidation, the content of TAG and LIPIN1 will gradually increase during embryo development and nuclear factor PPARα and PPARγ can also be affected by delipidation. The interaction of LIPIN1 and PPARα exists in porcine embryo.

Melatonin regulates lipid metabolism in porcine oocytes

It is being increasingly recognized that the processes of lipogenesis and lipolysis are important for providing an essential energy source during oocyte maturation and embryo development. Recent studies demonstrated that melatonin has a role in lipid metabolism regulation, including lipogenesis, lipolysis, and mitochondrial biogenesis. In this study, we attempted to investigate the effects of melatonin on lipid metabolism during porcine oocyte in vitro maturation. Melatonin treatment significantly enhanced the number of lipid droplets (LDs) and upregulated gene expression related to lipogenesis (ACACA, FASN, PPARγ, and SREBF1). Oocytes treated with melatonin formed smaller LDs and abundantly expressed several genes associated with lipolysis, including ATGL, CGI-58, HSL, and PLIN2. Moreover, melatonin significantly increased the content of fatty acids, mitochondria, and ATP, as indicated by fluorescent staining. Concomitantly, melatonin treatment upregulated gene expression related to fatty acid β-oxidation (CPT1a, CPT1b, CPT2, and ACADS) and mitochondrial biogenesis (PGC-1α, TFAM, and PRDX2). Overall, melatonin treatment not only altered both the morphology and amount of LDs, but also increased the content of fatty acids, mitochondria, and ATP. In addition, melatonin upregulated mRNA expression levels of lipogenesis, lipolysis, β-oxidation, and mitochondrial biogenesis-related genes in porcine oocytes. These results indicated that melatonin promoted lipid metabolism and thereby provided an essential energy source for oocyte maturation and subsequent embryonic development.

Live-cell quantification and comparison of mammalian oocyte cytosolic lipid content between species, during development, and in relation to body composition using nonlinear vibrational microscopy

Cytosolic lipids participate in the growth, development, and overall health of mammalian oocytes including many roles in cellular homeostasis. Significant emphasis has been placed on the study of lipids as a dynamic organelle, which in turn requires the development of tools and techniques to quantitate and compare how lipid content relates to cellular structure, function, and normalcy. Objectives of this study were to determine if nonlinear vibrational microscopy (e.g., coherent anti-Stokes Raman scattering or CARS microscopy) could be used for live-cell imaging to quantify and compare lipid content in mammalian oocytes during development and in relation to body composition; and compare its efficacy to methods involving cellular fixation and staining protocols. Results of this study demonstrate that CARS is able to identify lipids in live mammalian oocytes, and there exists quantifiable and consistent differences in percent lipid composition across ooctyes of different species, developmental stages, and in relation to body composition. Such a method of live-cell lipid quantification has (i) experimental power in basic cell biology, (ii) practical utility for identifying developmental predictive biomarkers while advancing biology-based oocyte/embryo selection, and (iii) ability to yield rationally supporting technology for decision-making in rodents, domestic species, and human assisted reproduction and/or fertility preservation.

Influence of Delipation on the Energy Metabolism in Pig Parthenogenetically Activated Embryos

This study was designed not only to measure the effect of delipation on the developmental viability of pig parthenogenetically activated (PA) embryos, but also to evaluate the changes of mitochondria DNA (mtDNA), reactive oxygen species (ROS) level, adenosine triphosphate (ATP) content and gene (Acsl3, Acadsb, Acaa2, Glut1) expression level at different stages after delipation. Results showed that no effect was observed on the cleavage ability, but significant lower blastocyst rate was obtained in delipated embryos. Copy number of mtDNA decreased gradually from MII to four-cell stages and subsequently kept consistent with blastocyst stage both in delipated and control embryos, but the copy number of mtDNA in delipated embryos was similar to that in the control groups no matter at which developmental stage was observed. Both in delipated and control embryos, ATP content progressive decreased from one-cell to blastocyst stages, while just at one-cell stage, a significant decrease of ATP level was observed in delipated embryos compared with that of control. The level of ROS increased obviously after delipation at cleavage stage, but no difference was seen at blastocyst stage. Finally, the expression level of genes related to fatty acids beta-oxidation (Acadsb and Acaa2) was decreased, while the expression level of genes related to glucose metabolism (Glut 1) was upregulated after delipation. In conclusion, the reduction of lipids in pig oocytes will affect the developmental competence of pig PA embryos by disturbed energy metabolism and ROS stress.