It is well-established that testicular spermatozoa are immature and acquire motility and fertilization capabilities during transit throughout the epididymis. The epididymis is a duct-like organ that connects the testis to the vas deferens and is comprised of four anatomical regions: the initial segment, caput, corpus, and cauda. Sperm maturation occurs during epididymal transit by the interaction of sperm cells with the unique luminal environment of each epididymal region. In this review we discuss the epididymis as an essential reproductive organ responsible for sperm concentration, maturation (including sperm motility acquisition and fertilizing ability), protection and storage. Importantly, we also discuss specific characteristics and roles of epididymal-derived exosomes (epididymosomes) in establishing sperm competency within the intricate process of reproduction. This review suggests that an increasing body of evidence is working to develop a complete picture of the role of the epididymis in male reproduction, offspring health, and disease susceptibility.

Sperm cryopreservation is one of the most important procedures in the development of biotechnologies for assisted reproduction. In some farm animals, the use of cryopreserved sperm has so many benefits for which relevance has become more evident in recent decades. Values for post-thaw sperm quality, however, are variable among species and within individuals of the same species. There is no standardized methodology for each of the stages of the cryopreservation procedure (andrological examination, semen collection, dilution, centrifugation, resuspension of the pellet with the freezing medium, packaging, freezing and post-thaw sperm evaluation), which also contributes to differences among studies. Cryotolerance markers of sperm and seminal plasma (SP) have been evaluated for prediction of ejaculate freezability. In addition, in previous research, there has been a focus on supplementing cryopreservation media with different substances, such as enzymatic and non-enzymatic antioxidants. In most studies, inclusion of these substances have led to improved post-thaw sperm quality and fertilizing capacity as a result of minimizing the adverse effects on sperm structure and function. Another approach is the use of different cryoprotectants. The aim with this review article is to provide an update on sperm cryopreservation in farm animals. The main detrimental effects of cryopreservation are described, including the negative repercussion on reproductive performance. Furthermore, the potential use of molecular biomarkers to predict sperm cryotolerance is discussed, as well as the addition of substances that can mitigate the harmful impact of freezing and thawing on sperm.

Infertility affects between 10 and 16% of couples worldwide. Twenty to 30% of cases of infertility are due to a male factor, 20–35% to a female factor, and 25–40% are due to both male and female factors. In ∼10–25% of cases, the precise underlying cause remains unclear. IVF or ICSI followed by embryo transfer can be very appropriate treatment options in cases of female tubal damage, ovulatory failure or male-factor infertility. While the use of IVF has been reported to be suitable for many infertile couples, normal IVF cycles can fail in some cases. While ICSI can represent a powerful alternative in cases of IVF failure, complete fertilization failure can still occur in 1–5% of ICSI cycles. This can be due to a variety of factors and while commonly attributed to deficiency of sperm factors, it is very likely that abnormalities in crucial oocyte factors could also play a key role. A critical literature review using PubMed was performed between April 2014 and July 2015 targeting studies concerning sperm and oocyte factors that could account for oocyte activation deficiency, and including studies of in vitro oocyte maturation in human oocytes, and animal models. Accumulating evidence indicates that phospholipase C zeta (PLCζ) is the sperm oocyte activation factor, although recent studies claim that another sperm protein known as post-acrosomal WWP-binding domain protein could also play a significant role in the activation of oocytes. The present review discusses our current understanding of these two proteins but emphasizes that defects in the molecular machinery within the oocyte that interacts with such sperm proteins may also represent an underlying cause of fertilization failure and infertility, especially in cases where there is no obvious indication for sperm deficiency. Abnormalities in such mechanisms are highly likely to exert influence over the pulsatile release of calcium within the ooplasm, the critical signal that controls oocyte activation events. These molecular targets within the oocyte are rarely, if ever, considered clinically. We therefore recommend that future diagnostic assays should be developed to consider the inositol triphosphate receptor, protein kinase C, proteins associated with stored operated calcium entry calcium/calmodulin-dependent protein kinase II and mitogen-activated protein kinase. Development of such assays would represent a significant step forward in the diagnosis of oocyte activation deficiency and may identify a series of potential therapeutic targets. The present review provides a general overview of how a combination of sperm and oocyte factors can underlie oocyte activation deficiency, but pays particular attention to the less appreciated role of the oocyte. Enhanced research within this realm is much warranted and may establish new approaches for the diagnosis and treatment of infertility.

It has long been thought that the factors affecting embryo and foetal development were exclusively maternally derived; hence, if issues regarding fertility and embryo development were to arise, the blame has traditionally been placed solely on the mother. An escalating interest in how paternal factors influence embryo development, however, has begun to prove otherwise. Evidence suggests that both seminal plasma (SP) and sperm contribute multiple factors that shape embryogenesis. This review thus focuses on the role that semen has in driving early embryonic development, and describes how paternal factors, such as SP, sperm centriole, sperm proteins, sperm RNA, sperm DNA, and its integrity, together with epigenetics, may influence the female reproductive tract and post-fertilization events. The important contributions of paternal factors to embryo development highlight the imperative need for further research in this area, which is sure to bring forth breakthroughs leading to improvements in infertility diagnosis and ART as well as reducing the risk of miscarriage. This review provides a comprehensive overview of the role of human semen in development of the early embryo, with the aim of providing a better understanding of the influence of SP and sperm on early embryonic divisions, gene and protein expression, miscarriage, and congenital diseases. PubMed searches were performed using the terms ‘sperm structure’, ‘capacitation’, ‘acrosome reaction’, ‘fertilization’, ‘oocyte activation’, ‘PLCζ’, ‘PAWP’, ‘sperm-borne oocyte activation factor’, ‘oocyte activation deficiency’, ‘sperm centriole’, ‘sperm transport’, ‘sperm mitochondria’, ‘seminal plasma’, ‘sperm epigenetics’, ‘sperm histone modifications’, ‘sperm DNA methylation’, ‘sperm-derived transcripts’, ‘sperm-derived proteins’, ‘sperm DNA fragmentation’, ‘sperm mRNA’, ‘sperm miRNAs’, ‘sperm piRNAs’, and ‘sperm-derived aneuploidy’. The reviewed articles were restricted to those published in English between 1980 and 2022. The data suggest that male-derived factors contribute much more than just the male haploid genome to the early embryo. Evidence indicates that semen contributes multiple factors that help shape the fate of embryogenesis. These male-derived factors include contributions from SP, the paternal centriole, RNA and proteins, and DNA integrity. In addition, epigenetic changes have an impact on the female reproductive tract, fertilization, and early stages of embryo development. For example, recent proteomic and transcriptomic studies have identified several sperm-borne markers that play important roles in oocyte fertilization and embryogenesis. This review highlights that several male-derived factors are required to work in tandem with female counterparts to allow for correct fertilization and development of the early embryo. A deeper understanding of the contributions of paternal factors that are shuttled over from the sperm cell to the embryo can shed light on how to improve ART from an andrological perspective. Further studies may aid in preventing the passing on of genetic and epigenetic abnormalities of paternal origin, thus decreasing the incidence of male factor infertility. In addition, understanding the exact mechanisms of paternal contribution may assist reproductive scientists and IVF clinicians in determining new causes of recurrent early miscarriage or fertilization failure. Understanding the various paternal factors that contribute to embryo development may help address the treatment of male infertility.