Intracytoplasmic Sperm Injection in Cattle

Factors affecting the intracytoplasmic sperm cell injection outcomes: A meta-analysis of porcine studies

BACKGROUND

Intracytoplasmic sperm cell injection (ICSI) has the potential to produce gene-edited (GE) pigs for biomedical research, but its success is limited. The factors impeding ICSI in pigs are impractical in-vivo oocyte production, incomplete cytoplasmic maturation of in-vitro matured (IVM) oocytes, inefficient methods for sperm selection and membrane removal, abnormal sperm nucleus decondensation, substandard protocols for oocyte stimulation, suboptimal in-vitro culture (IVC) systems, and high embryonic/fetal losses.

AIM OF REVIEW

The aim of this review is to investigate the effects of interventions in ICSI on oocyte activation, fertilization, cleavage, blastocyst, blastomere count, and live birth by means of robust statistical meta-analytical methods.

KEY SCIENTIFIC CONCEPTS OF REVIEW

A total of 61 studies published between 1905 ∼ 2024 met the inclusion criteria. The results of the meta-analysis suggested that manipulation in the IVM media did not improve oocyte developmental competency to blastocysts but increased the blastomere count, especially with the addition of thiol compounds. Consistently, manipulation with sperm was beneficial only for increasing the cleavage and blastomere count. Exogenous stimulation increased the relative risk (RR) for oocyte activation (10 %), fertilization (33 %), cleavage (18 %), and blastocyst formation (71 %) but did not affect the blastomere count. Chemical stimulation either pre- or post-ICSI was more beneficial than electrical stimulation. Manipulation of the culture increased the RR for oocyte activation (14 %) and fertilization (37 %) but did not benefit cleavage, blastocyst formation, or blastomere count. The subgroup analyses revealed that supplementation with thiol compounds was indeed beneficial. Our network meta-analysis also supported the findings of classical meta-analyses showing that cysteine, cysteamine, epidermal growth factor, amino acid supplementation in maturation and culture media, and Triton treatment of sperm improved blastocyst formation. The overall success rate of live births from total embryos transferred after ICSI was not greater than 2 %. Although, manipulations that were beneficial for ICSI outcomes were identified in this meta-analysis, however, areas where more robust data are needed to reach a conclusive decision are highlighted.

Bovine oocyte activation with bull or human sperm by conventional ICSI and Piezo-ICSI: Its relationship with PLCɀ activity

Background

The intracytoplasmic sperm injection (ICSI) technique has low efficiency in cattle. This has mainly been attributed to the oocyte activation failure due to oocyte and/or sperm factors.

Aim

Our aim was to evaluate the effect of conventional ICSI and Piezo-ICSI with bull or human sperm on bovine oocyte activation and embryo development and to assess its relationship with the phospholipase C zeta (PLCɀ) activity of both species.

Methods

In vitro matured bovine oocytes were randomly divided into five groups and were fertilized as follows: conventional ICSI using bovine sperm with chemical activation (control), conventional ICSI using bovine sperm, Piezo-ICSI using bovine sperm, conventional ICSI using human sperm, and Piezo-ICSI using human sperm. PLCɀ activity was determined in bull and human sperm samples.

Results

Within the groups using bull sperm, the oocytes fertilized by conventional ICSI had the lowest values of 2 pronuclei (PN) formation and cleavage, Piezo-ICSI increased both percentages and ICSI + chemical activation presented the highest 2 PN, cleavage, and blastocyst rates (p < 0.05). Within the groups using human sperm, the oocytes fertilized by Piezo-ICSI presented higher 2 PN and cleavage rates than those activated by conventional ICSI (p < 0.05). Piezo-ICSI with human sperm increased bovine oocyte activation as much as conventional ICSI + chemical activation with bovine sperm (p < 0.05). Higher values of PLCɀ activity were found in human sperm compared with bovine sperm (p < 0.05).

Conclusion

Our results suggest that the higher stability of the bovine sperm in combination with its relatively low content of PLCɀ impairs bovine oocyte activation after ICSI.

Fertility testing of preserved epididymal sperm by microinjection: A model for the rescue and utilization of genetically superior animals

Background

Epididymal sperm preservation is a simple conservation approach that can help prevent the loss of high genetic quality of farm animals. The chance of loss increases, especially during disease outbreaks or other interruptions to normal reproduction function.

Aim

This study looked into the ability of preserved ram epididymal sperm to fertilize oocytes. Due to motility becoming an issue following sperm storage for fertilization, the sperm microinjection known as intracytoplasmic sperm injection approach was employed.

Methods

The study was divided into two parts. First, involved the preservation of epididymal sperm at 5°C for 12 days. During preservation, sperm quality parameters namely motility, viability, intact membrane, acrosome, and Deoxyribonucleic acid (DNA) are evaluated every three days. For the fertility test in the second experiment, matured oocytes were injected with immotile sperm discovered in the last days of preservation. The presence of pronucleus development following in vitro culture is used as an indicator of sperm's ability to activate and fertilize oocytes.

Results

All sperm quality parameters significantly (p < 0.05) declined during preservation time. On day 12, motility was discovered to be 0%, but viable sperm, sperm with intact membrane, acrosome, and DNA remained at 41.86% ± 9.30%, 31.18% ± 5.15%, 21.88% ± 1.93%, and 33.35% ± 8.74%, respectively. On the fertility test, we inject immotile sperm from day 12 of preservation, which has the lowest motility found, into matured oocytes. Those sperms are able to activate (52.05% ± 7.15%) and fertilize (31.37% ± 1.75%) the injected oocytes, but their fertilizing ability is significantly lower (p < 0.05) when compared to the sperm derived from the ejaculate.

Conclusion

In this study, simple preservation of epididymal sperm reduces all sperm quality criteria, particularly motility. Using the microinjection approach preserved sperm which had no motility, still demonstrated its ability to activate and fertilize the oocytes. According to that, this study provides potential approaches and tools for using genetically superior animals that have lost their ability to execute regular fertilization, and also prolong reproduction function.

Phospholipase C Zeta 1 (PLCZ1): The Function and Potential for Fertility Assessment and In Vitro Embryo Production in Cattle and Horses

Phospholipase C Zeta 1 (PLCZ1) is considered a major sperm-borne oocyte activation factor. After gamete fusion, PLCZ1 triggers calcium oscillations in the oocyte, resulting in oocyte activation. In assisted fertilization, oocyte activation failure is a major cause of low fertility. Most cases of oocyte activation failures in humans related to male infertility are associated with gene mutations and/or altered PLCZ1. Consequently, PLCZ1 evaluation could be an effective diagnostic marker and predictor of sperm fertilizing potential for in vivo and in vitro embryo production. The characterization of PLCZ1 has been principally investigated in men and mice, with less known about the PLCZ1 impact on assisted reproduction in other species, such as cattle and horses. In horses, sperm PLCZ1 varies among stallions, and sperm populations with high PLCZ1 are associated with cleavage after intracytoplasmic sperm injection (ICSI). In contrast, bull sperm is less able to initiate calcium oscillations and undergo nuclear remodeling, resulting in poor cleavage after ICSI. Advantageously, injections of PLCZ1 are able to rescue oocyte failure in mouse oocytes after ICSI, promoting full development and birth. However, further research is needed to optimize PLCZ1 diagnostic tests for consistent association with fertility and to determine whether PLCZ1 as an oocyte-activating treatment is a physiological, efficient, and safe method for improving assisted fertilization in cattle and horses.

The mammalian preimplantation embryo: Its role in the environmental programming of postnatal health and performance

During formation of the preimplantation embryo several cellular and molecular milestones take place, making the few cells forming the early embryo vulnerable to environmental stressors than can impair epigenetic reprogramming and controls of gene expression. Although these molecular alterations can result in embryonic death, a significant developmental plasticity is present in the preimplantation embryo that promotes full-term pregnancy. Prenatal epigenetic modifications are inherited during mitosis and can perpetuate specific phenotypes during early postnatal development and adulthood. As such, the preimplantation phase is a developmental window where developmental programming can take place in response to the embryonic microenvironment present in vivo or in vitro. In this review, the relevance of the preimplantation embryo as a developmental stage where offspring health and performance can be programmed is discussed, with emphasis on malnutrition and assisted reproductive technologies; two major environmental insults with important implications for livestock production and human reproductive medicine.

Effect of bovine oocyte vitrification with EGTA and post-warming recovery with resveratrol on meiotic spindle, mitochondrial function, reactive oxygen species, and developmental competence

The present study aimed to determine the effects of the addition of EGTA to vitrification solutions and a post-warming recovery period supplemented with 1 μM resveratrol on meiotic spindle integrity, mitochondrial activity, ATP content, reactive oxygen species (ROS) levels, and developmental potential of partially denuded, vitrified-warmed bovine oocytes. Results of microtubule distribution and chromosomal arrangement indicated that resveratrol supplementation, irrespective to EGTA addition, reduced the incidence of abnormal meiotic spindles to similar levels of the control group. Mitochondrial membrane potential was similar in all groups, but ATP content was negatively affected by the vitrification-warming procedure and failed to recover after 4 h of post-warming culture. Resveratrol caused the reduction of ROS to lower levels of the control group, and showed the lowest ROS levels when combined with EGTA treatment. Oocytes in all vitrification groups presented lower developmental potential when compared to fresh oocytes. However, oocytes that underwent vitrification supplemented with EGTA and post-warming culture along with resveratrol showed higher developmental competence compared with vitrified-warmed oocytes not supplemented with resveratrol. The results of our study indicate that submitting vitrified-warmed, partially denuded bovine oocytes to a post-warming recovery period supplemented with 1 μM resveratrol improves vitrification outcomes. However, the benefits of EGTA on vitrification and warming of bovine oocytes need to be further investigated.

Bovine ICSI: limiting factors, strategies to improve its efficiency and alternative approaches

Intracytoplasmic sperm injection (ICSI) is an assisted reproductive technique mainly used to overcome severe infertility problems associated with the male factor, but in cattle its efficiency is far from optimal. Artificial activation treatments combining ionomycin (Io) with 6-dimethylaminopurine after piezo-ICSI or anisomycin after conventional ICSI have recently increased the blastocyst rate obtained. Compounds to capacitate bovine spermatozoa, such as heparin and methyl-β-cyclodextrin and compounds to destabilize sperm membranes such as NaOH, lysolecithin and Triton X-100, have been assessed, although they have failed to substantially improve post-ICSI embryonic development. Disulfide bond reducing agents, such as dithiothreitol (DTT), dithiobutylamine and reduced glutathione, have been assessed to decondense the hypercondensed head of bovine spermatozoa, the two latter being more efficient than DTT and less harmful. Although piezo-directed ICSI without external activation has generated high fertilization rates and modest rates of early embryo development, other studies have required exogenous activation to improve the results. This manuscript thoroughly reviews the different strategies used in bovine ICSI to improve its efficiency and proposes some alternative approaches, such as the use of extracellular vesicles (EVs) as 'biological methods of oocyte activation' or the incorporation of EVs in the in vitro maturation and/or culture medium as antioxidant defence agents to improve the competence of the ooplasm, as well as a preincubation of the spermatozoa in estrous oviductal fluid to induce physiological capacitation and acrosome reaction before ICSI, and the use of hyaluronate in the sperm immobilization medium.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.