Lipid droplets in mammalian eggs are utilized during embryonic diapause.

Embryonic diapause (ED) is a temporary arrest of an embryo at the blastocyst stage when it waits for the uterine receptivity signal to implant. ED used by over 100 species may also occur in normally "nondiapausing" mammals when the uterine receptivity signal is blocked or delayed. A large number of lipid droplets (LDs) are stored throughout the preimplantation embryo development, but the amount of lipids varies greatly across different mammalian species. Yet, the role of LDs in the mammalian egg and embryo remains unknown. Here, using a mouse model, we provide evidence that LDs play a crucial role in maintaining ED. By mechanical removal of LDs from zygotes, we demonstrated that delipidated embryos are unable to survive during ED. LDs are not essential for normal prompt implantation, without ED. We further demonstrated that with the progression of ED, the amount of intracellular lipid reduces, and composition changes. This decrease in lipid is caused by a switch from carbohydrate metabolism to lipid catabolism in diapausing blastocysts, which also exhibit increased release of exosomes reflecting elevated embryonic signaling to the mother. We have also shown that presence of LDs in the oocytes of various mammals positively corelates with their species-specific length of diapause. Our results reveal the functional role of LDs in embryonic development. These results can help to develop diagnostic techniques and treatment of recurrent implantation failure and will likely ignite further studies in developmental biology and reproductive medicine fields.

Parental ageing and Assisted Reproduction Technologies: analysis of risk of chronic diseases in the progeny / Pózne rodzicielstwo i rozród wspomagany: analiza ryzyka wystapienia chorób przewleklych u potomstwa.

Conception of a child at advanced parental age (> 35 years) has been steadily increasing in recent decades, especially in developed countries. Socio-economic factors, effective contraceptives, and the availability of Assisted Reproduction Technologies (ART) have a direct impact on postponing the decision to have a baby. ART enables reproductive success for people diagnosed as infertile or with reduced possibilities of becoming pregnant due to concomitant pathologies. Epidemiological studies indicate that both advanced parental age and ART are associated with pathologies of pregnancy, such as gestational diabetes, risk of pre-eclampsia, miscarriage, placental abruption, preterm labor, stillbirth, neurodevelopmental disorders and chronic disease of the offspring. In our work, we will focus on the available information on metabolic changes that increase the risk of developing cardiovascular diseases in the offspring of parents at an advanced age and conceived through ART. Finally, we will address the sources of the observed disturbances at the gamete and embryo level, related to oxygen stress, epigenetic modifications and DNA damage, considering possible rescue actions.

Nile Red and BODIPY Staining of Lipid Droplets in Mouse Oocytes and Embryos.

Lipid droplets (LDs) are intracellular structures composed of hydrophobic lipids. Their amount in oocytes and embryos varies among the mammalian species and even among different strains of the same species. Here we describe a method to stain LDs, which can be applied to previously fixed mouse oocytes and embryos. This method is based on fluorescent dyes, Nile red and BODIPY, which allow visualization and quantification of LDs using conventional and confocal fluorescence microscopy.

DNA damage in preimplantation embryos and gametes: specification, clinical relevance and repair strategies.

BACKGROUND: DNA damage is a hazard that affects all cells of the body. DNA-damage repair (DDR) mechanisms are in place to repair damage and restore cellular function, as are other damage-induced processes such as apoptosis, autophagy and senescence. The resilience of germ cells and embryos in response to DNA damage is less well studied compared with other cell types. Given that recent studies have described links between embryonic handling techniques and an increased likelihood of disease in post-natal life, an update is needed to summarize the sources of DNA damage in embryos and their capacity to repair it. In addition, numerous recent publications have detailed novel techniques for detecting and repairing DNA damage in embryos. This information is of interest to medical or scientific personnel who wish to obtain undamaged embryos for use in offspring generation by ART. OBJECTIVE AND RATIONALE: This review aims to thoroughly discuss sources of DNA damage in male and female gametes and preimplantation embryos. Special consideration is given to current knowledge and limits in DNA damage detection and screening strategies. Finally, obstacles and future perspectives in clinical diagnosis and treatment (repair) of DNA damaged embryos are discussed. SEARCH METHODS: Using PubMed and Google Scholar until May 2021, a comprehensive search for peer-reviewed original English-language articles was carried out using keywords relevant to the topic with no limits placed on time. Keywords included 'DNA damage repair', 'gametes', 'sperm', 'oocyte', 'zygote', 'blastocyst' and 'embryo'. References from retrieved articles were also used to obtain additional articles. Literature on the sources and consequences of DNA damage on germ cells and embryos was also searched. Additional papers cited by primary references were included. Results from our own studies were included where relevant. OUTCOMES: DNA damage in gametes and embryos can differ greatly based on the source and severity. This damage affects the development of the embryo and can lead to long-term health effects on offspring. DDR mechanisms can repair damage to a certain extent, but the factors that play a role in this process are numerous and altogether not well characterized. In this review, we describe the multifactorial origin of DNA damage in male and female gametes and in the embryo, and suggest screening strategies for the selection of healthy gametes and embryos. Furthermore, possible therapeutic solutions to decrease the frequency of DNA damaged gametes and embryos and eventually to repair DNA and increase mitochondrial quality in embryos before their implantation is discussed. WIDER IMPLICATIONS: Understanding DNA damage in gametes and embryos is essential for the improvement of techniques that could enhance embryo implantation and pregnancy success. While our knowledge about DNA damage factors and regulatory mechanisms in cells has advanced greatly, the number of feasible practical techniques to avoid or repair damaged embryos remains scarce. Our intention is therefore to focus on strategies to obtain embryos with as little DNA damage as possible, which will impact reproductive biology research with particular significance for reproductive clinicians and embryologists.