Sperm DNA fragmentation and its role in wildlife conservation

Chromatin Dispersion Test to Asses DNA Damage in Cervical Epithelial Cells

The chromatin dispersion test (CDT) is based on the removal of nuclear proteins under the assumption that cells with fragmented DNA produce a typical halo of circular DNA loops, which is absent in cells with non-fragmented DNA. This method represents a simple, rapid, accurate, highly reproducible, and inexpensive technique to assess nuclear DNA damage in somatic cells. The visualization of DNA damage and the capacity of the test to provide a threshold value to discriminate between high and low levels of cervical lesions would aid in determining the malignant transformation. All of these advantages associated with the CDT protocol could promote this technique as a tool for the quick and reliable diagnosis of cervical epithelial disorders, even at primary-care centers.

Conservation Biology and Reproduction in a Time of Developmental Plasticity

The objective of this review is to ask whether, and how, principles in conservation biology may need to be revisited in light of new knowledge about the power of epigenetics to alter developmental pathways. Importantly, conservation breeding programmes, used widely by zoological parks and aquariums, may appear in some cases to reduce fitness by decreasing animals' abilities to cope when confronted with the 'wild side' of their natural habitats. Would less comfortable captive conditions lead to the selection of individuals that, despite being adapted to life in a captive environment, be better able to thrive if relocated to a more natural environment? While threatened populations may benefit from advanced reproductive technologies, these may actually induce undesirable epigenetic changes. Thus, there may be inherent risks to the health and welfare of offspring (as is suspected in humans). Advanced breeding technologies, especially those that aim to regenerate the rarest species using stem cell reprogramming and artificial gametes, may also lead to unwanted epigenetic modifications. Current knowledge is still incomplete, and therefore ethical decisions about novel breeding methods remain controversial and difficult to resolve.

Quick assessment of DNA damage in cervical epithelial cells using a chromatin dispersion test

PURPOSE

This study was aimed to quantify genomic DNA breakages in the cervical epithelium cells of patients diagnosed with different grades of cervical lesions using a quick test based on chromatin dispersion after controlled protein depletion. The association between the progressive stages of cervical dysplasia and the levels of DNA damage, taking into account the presence of papillomavirus human (HPV) infection, was investigated.

METHODS

A hospital-based unmatched case-control study was conducted during 2018 with a sample of 78 women grouped according to histological diagnosis as follows: 23 women with low grade-squamous intraepithelial lesion (LG-SIL), 34 women with high grade- squamous intraepithelial lesion (HG-SIL), and three women with cervical carcinoma (CC). In parallel, 15 women without cervical lesions were included as a Control cohort. DNA damage levels in cervical epithelial cells were assessed using the chromatin dispersion test (CDT) and controlled in parallel with DNA breakage detection coupled with florescent in situ hybridization (DBD‒FISH) using whole genomic DNA probes.

RESULTS

CDT produces different morphotypes in the cervical epithelium that can be associated with the level of DNA breakage revealed with DBD‒FISH. A significant increase of DNA damage was correlated with the histological progression of the patients and human papillomavirus (HPV) infection.

CONCLUSION

The CDT is a simple, accurate and inexpensive morphological bioassay to identify different levels DNA damage that can be associated with the level of abnormal cells present in the cervical epithelium in patients who commonly present HPV infection.

Characteristics of capercaillie (Tetrao urogallus) semen analysed with flow cytometry combined with fertility results

In order to increase the reproductive indices of capercaillie kept in closed breeding facilities, it is necessary to constantly expand the methods of better understanding the characteristics of sperm and their fertilizing potency. The aim of the study was to analyse selected features of capercaillie sperm using flow cytometry and their connection with fertility results. The study included five males, three of which were kept in a family group with eight females and two were kept alone. For sperm viability, acrosome integrity, mitochondrial potential and DNA defragmentation were assessed. Paternity analyses were performed in order to confirm the paternity of the individual and to link the evaluated semen traits with reproductive success. Analyses carried out in the flow cytometer showed any significant differences between males in sperm characteristics. In the semen of male No. 101, the father of all chicks from the analysed family group, 91.3% of live sperm, 91.5% with intact acrosome, 83.6% with active mitochondria and 2.0% with DNA defragmentation were observed. The average fertility rate was 71.0%, and chick hatchability was 100%. Using flow cytometry in the analysis of capercaillie semen and its connection with the results of natural mating, we were able to obtain deeper knowledge about new sperm characteristics that were not examined before and which in the future may be helpful in selecting males for the reproductive flocks and developing assisted reproduction techniques.

DNA fragmentation index (DFI) as a measure of sperm quality and fertility in mice

Although thousands of genetically modified mouse strains have been cryopreserved by sperm freezing, the likelihood of cryorecovery success cannot be accurately predicted using conventional sperm parameters. The objective of the present study was to assess the extent to which measurement of a sperm DNA fragmentation index (DFI) can predict sperm quality and fertility after cryopreservation. Using a modified TUNEL assay, we measured and correlated the DFI of frozen-thawed sperm from 83 unique mutant mouse strains with sperm count, motility and morphology. We observed a linear inverse correlation between sperm DFI and sperm morphology and motility. Further, sperm DFI was significantly higher from males with low sperm counts compared to males with normal sperm counts (P < 0.0001). Additionally, we found that viable embryos derived using sperm from males with high DFI (62.7 ± 7.2% for IVF and 73.3 ± 8.1% for ICSI) failed to litter after embryo transfer compared to embryos from males with low DFI (20.4 ± 7.9% for IVF and 28.1 ± 10.7 for ICSI). This study reveals that measurement of DFI provides a simple, informative and reliable measure of sperm quality and can accurately predict male mouse fertility.

Adverse effects of in vitro manipulation of spermatozoa

Development of in vitro reproduction techniques has not only offered some infertile couples the possibility to have a child, it also revolutionized animal reproduction. Although in vitro reproduction techniques for humans or domestic and non-domestic animals have been designed to mimic in vivo conditions, modifications due to environmental effects or in vitro manipulation of gametes and embryos are unavoidable. For male gametes, in vitro manipulations include techniques to select spermatozoa, cryopreservation and other incubation procedures, during which spermatozoa may be exposed to oxidative stress and other insults that may damage their functions and DNA. The aim of this review is to provide an overview of key studies reporting sperm damage during in vitro manipulation, with particular focus on effects on DNA integrity, a fundamental factor for fertilization and transmission of paternal genetic information to offspring.

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking.

Challenges associated with the development and transfer of assisted breeding technology in marsupials and monotremes: lessons from the koala, wombat and short-beaked echidna

This reflective review describes how a research model, which was originally established for the successful AI of the koala (Phascolarctos cinereus), is currently being developed and extended to the wombat (Lasiorhinus latifrons and Vombatus ursinus) and short-beaked echidna (Tachyglossus aculeatus). The research model centres around the establishment of an AI program and involves: (1) semen collection, evaluation and preservation, requiring an understanding of male reproductive physiology and gamete biology; (2) timing of insemination, based on a knowledge of oestrous cycle and gestation physiology and oestrous behaviour; and (3) the appropriate placement of semen, which relies on an accurate description of female reproductive anatomy. Published and unpublished studies of assisted breeding technology (ABT) development in all three species of Australian mammals reported in this review (koala, wombat and short-beaked echidna) clearly demonstrate the importance of recognising species-specific variation in reproductive biology. Even in closely related species, such as the koala and wombat, subtle differences in reproductive physiology can hinder the transfer of ABT across species. Significant progress in marsupial and monotreme ABT will also require adequate access to captive wildlife colonies (zoos, university collections and private partners) in sufficient numbers in order to conduct quality science.

Using the Koala (Phascolarctos cinereus) as a Case Study to Illustrate the Development of Artificial Breeding Technology in Marsupials: an Update

The successful development and application of an assisted breeding program in any animal relies primarily on a thorough understanding of the fundamental reproductive biology (anatomy, physiology and behaviour) of the species in question. Surely, the ultimate goal and greatest hallmark of such a program is the efficacious establishment of a series of reliable techniques that facilitate the reproductive and genetic management of fragmented populations, both in captivity and in the wild. Such an achievement is all that more challenging when knowledge of the reproductive biology of that species is essentially rudimentary and without adequate models to compare to. Using the koala (Phascolarctos cinereus) as a case study, this chapter provides insights into the development of a concept that began as small undergraduate student project but that subsequently evolved into the first-ever successful artificial insemination of a marsupial. Apart from this historical perspective, we shall also provide a brief review of the current reproductive biology of the koala, discuss technical elements of current assisted breeding technology of this species, its application to the closely related wombat, and the potential role it might play in helping to conserve wild koala populations in the form of a live koala genome bank. There is little doubt that the unique reproductive biology and tractability of the koala has been a benefit rather than a hindrance to the success of artificial breeding in this species.

Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa

There is growing concern over the effect of sperm cryopreservation on DNA integrity and the subsequent development of offspring generated from this cryopreserved material. In the present study, membrane integrity and DNA stability of Xenopus laevis and Xenopus tropicalis spermatozoa were evaluated in response to cryopreservation with or without activation, a process that happens upon exposure to water to spermatozoa of some aquatic species. A dye exclusion assay revealed that sperm plasma membrane integrity in both species decreased after freezing, more so for X. laevis than X. tropicalis spermatozoa. The sperm chromatin dispersion (SCD) test showed that for both X. tropicalis and X. laevis, activated frozen spermatozoa produced the highest levels of DNA fragmentation compared with all fresh samples and frozen non-activated samples (P<0.05). Understanding the nature of DNA and membrane damage that occurs in cryopreserved spermatozoa from Xenopus species represents the first step in exploiting these powerful model organisms to understand the developmental consequences of fertilising with cryopreservation-damaged spermatozoa.

Reduced sperm DNA longevity is associated with an increased incidence of still born; evidence from a multi-ovulating sequential artificial insemination animal model

PURPOSE

Using a rabbit model, we assessed the influence of sperm DNA longevity on female reproductive outcomes.

METHODS

Semen was collected from 40 bucks, incubated at 38 °C for 24 h, and the rate of sperm DNA fragmentation (rSDF) was determined using the sperm chromatin dispersion assay. Males were allocated into high rSDF (>0.5 units of increase per hour) or low rSDF (<0.5 units of increase per hour) groups. High and low rSDF semen samples were sequentially artificially inseminated into the same doe to reduce female factor variability, and pregnancy outcomes were recorded.

RESULTS

While there was no difference in SDFs between rSDF groups immediately after collection (T0), differences were significant after 2 h of incubation; SDFs determined at collection and rSDF behaved as independent characters (Pearson correlation = 0.099; P = 0.542). Following artificial insemination, the rate of stillborn pups was significantly higher in does inseminated by males with a high rSDF (14/21) compared to those with low rSDF (15/6); (contingency χ(2) 5.19; p = 0.022). The risk of stillborn when low rSDF rabbits were used for insemination was 0.16, but increased to 0.36 when high rSDF animals were used (odds ratio = 2.85; 95 % confidence interval = 1.4-2.7).

CONCLUSION(S)

Dynamic assessment of SDF coupled with natural multiple ovulation, high fecundity of the rabbit and control over female factor influence, provided a useful experimental model to demonstrate the adverse effect of reduced sperm DNA longevity on reproductive outcome.