Reproduction, Fertility and Development

The control of oestrus and ovulation is critical for achieving advanced puberty, out-of-season breeding and synchronised lambing, plus allowing artificial insemination and embryo production. Classical protocols should be reconsidered due to current better knowledge of ovarian dynamics and increasing public concern about animal welfare, food safety and the environmental impact of treatments. The present manuscript offers an overview of state-of-the-art methods and suggests ways for improving current protocols.

Cryopreservation of a mare’s oocytes could become an important strategy in horse breeding if the foaling rates were better. Here we discuss the most important technical and biological factors affecting the success of oocyte vitrification in the horse, referring to novel approaches in other species. Further research is needed to optimise oocyte vitrification in order to achieve high blastocyst and foaling rates.

The likelihood of foaling and the foal sex ratio are influenced by the speed of in vitro embryo development, with a higher likelihood of live birth and a colt after transfer of Day 7 than Day 8 in vitro-produced blastocysts. Frozen–thawed IVP embryos survive better when transferred into recipient mares on Day 4 after ovulation.

The gonadotropic hormones used for superovulation in mice may influence the quantity and quality of resulting oocytes and embryo development following in vitro fertilisation (IVF) and embryo culture. We evaluated quantitative, morphometric, subcellular characteristics, IVF and embryonic developmental competence of the oocytes derived after anti-inhibin serum or pregnant mare serum gonadotrophin administration. This information would be useful for those who are interested in oocyte and embryo development, genetic modifications and assisted reproductive technologies in mice.

Male infertility is a worldwide problem because of impaired sperm quality; new approaches are indispensable for investigations at the molecular level. We studied two proteins necessary for proper sperm differentiation and found altered expression in the testes and spermatozoa of infertile men. Our results give new insight into the mechanisms of spermatogenesis, raising the possibility of using these proteins as new markers of normal fertility.

MicroRNA-145 (miR-145) is important for embryo development because it regulates pluripotency. Although the miR-145 expression pattern is similar in nuclear transferred (NT) and IVF embryos during development, miR-145 expression is higher in NT than IVF embryos at all stages of development. Deceasing miR-145 expression by treating NT embryos with an miR-145 inhibitor could be used to increase the blastocyst rate and improve embryo quality.

Connexin (Cx) 43 is the main testicular factor controlling the differentiation and maturation of Sertoli cells (SCs); however, the endogenous factors regulating Cx43 and its downstream signalling pathways are unclear. This study investigated how Wilms’ tumour 1 (WT1) regulates the expression of Cx43 in SCs and determined the signalling pathway involved. In this study, WT1 was negatively regulated by Cx43 expression via a non-canonical Wnt signalling pathway.

It is well known that feline ovarian follicles are sensitive to cryopreservation procedures. Betaine microencapsulated in CaCO₃ appears as a compound to improve the survival of feline preantral follicles submitted to vitrification within the ovarian tissue. Additionally, microencapsulated betaine was able to increase mitochondrial activity without induce oxidative stress.

We have previously shown that implantation of dissociated neonatal pig testis cells under the back skin of immunodeficient mice can lead to regeneration of functional testis tissue, although the results were inconsistent and inefficient. Here, by examining several factors, we dramatically improved the consistency, efficiency and predictability of the model. The testis cell implantation model can be used as an accessible system to study and manipulate testis tissue development and regeneration, and as a unique model for fertility preservation of prepubertal boys undergoing gonadotoxic cancer treatments.

Di-(2-ethylhexyl) phthalate (DEHP) is ubiquitous in the environment. This study found that low and high doses of DEHP had opposite effects on female puberty onset, hypothalamic kisspeptin expression and reproductive hormones. These results contribute to the comprehensive evaluation of DEHP toxicity on the human reproductive system.

Upregulated lipolysis is commonly associated with metabolic disorders and deleterious effects on female fertility. The role of the oviduct in this process remains insufficiently investigated due to complicating factors such as multiple-metabolite interactions and difficult organ accessibility. Our in vitro results suggest a direct embryotoxicity induced by elevated concentrations of non-esterified fatty acids within the earliest embryonic environment, through a reduced oviductal ability to support and protect early embryo development.

Di-2-ethylhexyl phthalate (DEHP) is the most widely used plasticiser and human exposure to DEHP is ubiquitous in daily life. We found that DEHP had no effect on human sperm function at the doses that cover the concentrations detected in human semen, but that mono-2-ethylhexyl phthalate (the main metabolite of DEHP) affected human sperm function by increasing sperm [Ca²⁺]_i and tyrosine phosphorylation. These data add to our understanding of the effects of DEHP on male reproduction.

Early embryo survival and successful implantation are of obvious fundamental importance in establishing a pregnancy in cattle, yet have received surprisingly little attention. A comprehensive review of the literature has identified early development of ovarian follicles and the first 3 weeks of embryo development as critical periods that determine reproductive success. A deeper understanding of these critical periods in female reproductive biology will inform the next step change in improving the efficiency of natural and assisted reproduction in cattle.

MicroRNAs (miRNAs) are essential for testicular development and spermatogenesis. Using small RNA sequencing technology, 531 mature miRNAs were identified in Mongolian horse testes, among which 107 miRNAs were differentially expressed between immature and mature testes. These findings identify miRNAs as key factors in the development of the testes and spermatogenesis in the Mongolian horse.

This study aimed to determine the effect of asynchrony between embryo age and female reproductive tract cycle stage on subsequent embryo development in cattle. Transfer of embryos to an oviduct 2 days in advance of the embryo reduced embryo development on Days 4, 7 and 15. Accelerated conceptus development at Day 15 was likely due to effects of progesterone on the endometrium. The results highlight the importance of synchrony between the embryo and the oviduct and uterus in establishing pregnancy.

Despite the importance of glucose transport for supporting sperm motility, glucose metabolic pathways are poorly characterised in chicken spermatozoa. We found that the glucose transporter GLUT1 is specifically localised to the midpiece and flagellum, and contributes to flagellar motility by ATP production via glycolysis and oxidative phosphorylation. These results provide new insights into energy production pathways responsible for avian sperm motility.

The uterine environment is paramount to fertility, yet little is known about uterine proteomic differences between mares with a healthy uterus and mares with uterine disease. This study demonstrated qualitative and quantitative differences between healthy mares and mares with endometritis or fibrotic endometrial degeneration. The results can serve as a basis for finding specific biomarkers of uterine health and disease.

Seminal plasma, the fluid that, together with sperm cells, makes up the semen, contains antioxidant enzymes. This study investigated whether seminal plasma is able to counteract induced oxidative stress in donkey spermatozoa. Following induction of oxidative stress with exogenous hydrogen peroxide, we observed that seminal plasma has a limited effect in modulating the response of donkey spermatozoa to that stress.