Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Embryo manipulation via assisted reproductive technology and epigenetic asymmetry in mammalian early development

The early stage of mammalian development from fertilization to implantation is a period when global and differential changes in the epigenetic landscape occur in paternally and maternally derived genomes, respectively. The sperm and egg DNA methylation profiles are very different from each other, and just after fertilization, only the paternally derived genome is subjected to genome-wide hydroxylation of 5-methylcytosine, resulting in an epigenetic asymmetry in parentally derived genomes. Although most of these differences are not present by the blastocyst stage, presumably due to passive demethylation, the maintenance of genomic imprinting memory and X chromosome inactivation in this stage are of critical importance for post-implantation development. Zygotic gene activation from paternally or maternally derived genomes also starts around the two-cell stage, presumably in a different manner in each of them. It is during this period that embryo manipulation, including assisted reproductive technology, is normally performed; so it is critically important to determine whether embryo manipulation procedures increase developmental risks by disturbing subsequent gene expression during the embryonic and/or neonatal development stages. In this review, we discuss the effects of various embryo manipulation procedures applied at the fertilization stage in relation to the epigenetic asymmetry in pre-implantation development. In particular, we focus on the effects of intracytoplasmic sperm injection that can result in long-lasting transcriptome disturbances, at least in mice.

Safety, efficacy and efficiency of laser-assisted IVF in subfertile mutant mouse strains

In the present report we studied the safety, efficacy and efficiency of using an infrared laser to facilitate IVF by assessing fertilization, development and birth rates after laser-zona drilling (LZD) in 30 subfertile genetically modified (GM) mouse lines. We determined that LZD increased the fertilization rate four to ten times that of regular IVF, thus facilitating the derivation of 26 of 30 (86.7%) GM mouse lines. Cryopreserved two-cell stage embryos derived by LZD-assisted IVF were recovered and developed to blastocysts in vitro at the same rate as frozen-thawed embryos derived by regular IVF. Surprisingly after surgical transfer to pseudopregnant recipients the birth rate of embryos derived by LZD-assisted IVF was significantly lower than that of embryos derived by regular IVF. However this result could be completely mitigated by the addition of 0.25 M sucrose to the culture medium during LZD which caused the oocyte to shrink in volume relative to the perivitelline space. By increasing the distance from the laser target site on the zona pellucida, we hypothesize that the hyperosmotic effect of sucrose reduced the potential for laser-induced cytotoxic thermal damage to the underlying oocytes. With appropriate preparation and cautious application, our results indicate that LZD-assisted IVF is a safe, efficacious and efficient assisted reproductive technology for deriving mutant mouse lines with male factor infertility and subfertility caused by sperm-zona penetration defects.

Efficient production of transgenic mice by intracytoplasmic injection of streptolysin-O-treated spermatozoa

Many methods for efficient production of transgenic animals for biomedical research have been developed. Despite great improvements in transgenesis rates resulting from the use of intracytoplasmic sperm injection (ICSI), the ICSI-based sperm-mediated gene-transfer (iSMGT) technique is still not optimal in terms of sperm permeabilization efficiency and subsequent development. Here, we demonstrate that streptolysin-O (SLO) can efficiently permeabilize mouse spermatozoa, leading to improved developmental competence and high transgenesis rates in iSMGT embryos and pups. In particular, the most efficient production of iSMGT-transgenic embryos resulted from pretreatment with 5 U/ml SLO for 30 min and co-incubation with 1.0 ng/µl of an EGFP expression vector. By incubating spermatozoa with Cy-3-labelled DNA, we found that fluorescence intensity was prominently detected in the head region of SLO-treated spermatozoa. In addition, blastocyst development rate and blastomere survival were greatly improved by iSMGT using SLO-treated spermatozoa (iSMGT-SLO) as compared to freeze-thawed spermatozoa. Consistent with this, a high proportion of transgenic offspring was obtained by iSMGT-SLO after transfer into foster mothers, reaching 10.6% of the number of oocytes used (42.3% among pups). Together with successful germline transmission of transgenes in all founders analyzed, our data strongly suggest that SLO makes spermatozoa amenable to exogenous DNA uptake, and that the iSMGT-SLO technique is an efficient method for production of transgenic animals for biomedical research.

Sperm capacitation combined with removal of the sperm acrosome and plasma membrane enhances paternal nucleus remodelling and early development of bovine androgenetic embryos

The androgenetic embryo is a useful model for functional analysis of the paternal genome during embryogenesis. However, few studies have focused on the factors involved in the suppressed developmental competence of such embryos or why sperm cloning-derived androgenetic embryos fail to develop beyond the morula stage in large domestic animals. To overcome this developmental failure, we tried to improve sperm decondensation, as well as to enhance embryonic development by sperm capacitation and removal of the acrosome and plasma membrane before injection of the spermatozoa. Before injection of the spermatozoa, we quantified the effects of sperm capacitation combined with sperm pretreatment on the acrosome and plasma membrane status. We also evaluated sperm decondensation potential, sperm viability and chromatin integrity. Immunostaining data showed that the sperm acrosome and plasma membrane could be more efficiently removed after capacitation. Dithiothreitol-induced sperm decondensation potential was improved with capacitation and removal of the acrosome and plasma membrane. Although most spermatozoa lost viability after pretreatment, their chromatin remained integrated. The patterns of paternal chromatin remodelling within uncleaved androgenetic embryos and the nucleus morphology of cleaved embryos indicated that capacitation combined with membrane disruption could make injected spermatozoa decondense synchronously not only with each other, but also with the developmental pace of the ooplasm. We successfully produced androgenetic blastocysts, and efficiency increased with sperm pretreatment. In conclusion, sperm decondensation and the early development of androgenetic embryos were enhanced with sperm capacitation and removal of the acrosome and plasma membrane prior to sperm injection.

Uniparental embryos in the study of genomic imprinting

Nuclear transplantation has been used to study genomic imprinting. Available nuclear transfer methods include pronuclear transfer (PNT), intracytoplasmic sperm injection, and round spermatid injection. By generating uniparental embryos that have exclusively paternal or maternal genomes, it is possible to study the functions of the parental genomes separately. It is possible to compare functions in haploid and diploid states. In addition, nuclear transfer allows the effects of the ooplasm, including mitochondria, to be distinguished from effects of the maternally inherited chromosomes. PNTs can also be used to study epigenetic modifications of the parental genomes by the ooplasm. This chapter reviews the methods employed to generate uniparental embryonic constructs for these purposes.

Sperm pretreatment with dithiothreitol increases male pronucleus formation rates after intracytoplasmic sperm injection (ICSI) in swamp buffalo oocytes

Failure of male pronucleus formation has hampered the success of intracytoplasmic sperm injection (ICSI) in swamp buffalo. The aim of the present study was to improve male pronucleus formation by pretreating sperm with various chemicals before ICSI. In Experiments1 and 2, sperm were treated according to one of the following protocols: (1) 0.1% Triton-X 100 (TX) for 1 min, (2) 10 µM calcium ionophore (CaI) for 20 min, (3) freezing and thawing (FT) without any cryoprotectant, or (4) no treatment (control). These sperm treatment groups then either did or did not receive additional sperm treatment with 5 mM dithiothreitol (DTT) for 20 min. Acrosomal integrity (Experiment 1) and DNA fragmentation (Experiment 2) were evaluated in the sperm before ICSI. In Experiment 3, oocytes matured in vitro were subjected to ICSI using pretreated sperm as described above and then were cultured either with or without activation. The TX- and CaI-treated sperm caused an increase in the number of acrosome-loss sperm, whereas the FT treatment and control increased the proportion of acrosome-reacted sperm (P<0.05). The DNA fragmentation did not differ among treatments (P>0.05). At 18 h post-ICSI, pronucleus (PN) formation was found only in activated oocytes. The majority of the activated ICSI oocytes contained intact sperm heads. Normal fertilization was observed in the CaI and FT treatment groups and control group when sperm were treated with DTT before ICSI. In conclusion, DTT treatment of sperm with reacted acrosomes before ICSI together with activation of the ICSI oocytes is important for successful male pronucleus formation.

Fertilization studies and assisted fertilization in mammals: their development and future

Studies of mammalian fertilization progressed very slowly in the beginning because of difficulties in obtaining a large quantity of fully mature eggs at one time. With progression of techniques to collect and handle eggs and spermatozoa, research in mammalian fertilization advanced rapidly. Today, far more papers are published on mammalian gametes and fertilization than those of all other animals combined. The development of assisted fertilization and related technologies revolutionized basic research as well as human reproductive medicine and animal husbandry. Reproduction is fundamental to human and animal lives. The author lists a few subjects of his personal interest for further development of basic and applied research of gametes and fertilization. Each reader will probably have more exciting subjects of future investigation.

Intracytoplasmic sperm injection (ICSI) in small ruminants

Small ruminants are an important component of the global production systems of meat and wool, and their reproductive biology is well known. However, the incorporation of assisted reproduction techniques (ART) in the production systems of small ruminants is not as well developed as for other domestic species. Normally, production systems that incorporate ARTs are restricted to artificial insemination or in vivo embryo transfer. Intracytoplasmic sperm injection (ICSI) is one of the ARTs techniques reported for small ruminants and consists of the injection of spermatozoa inside an oocyte, bypassing the natural process of sperm-oocyte interaction. In goats and sheep, there are few live births by ICSI reported, with no reports from other species of small ruminants. Currently, there has not been intensive research about ICSI in small ruminants. However, ICSI has potentially important applications in animal production systems, primarily its use with semen of valued animals, with epididymal sperm, in the fertilization of prepubertal or cryopreserved oocytes. Other applications include more advanced techniques, such as transgenic-ICSI or its combination with spermatogonial transplantation. In this article, we review the "state of the art" of this technique in small ruminants including its historical development, research needs for its improvement and future applications.

Generation of genetically modified mice by oocyte injection of androgenetic haploid embryonic stem cells

Haploid cells are amenable for genetic analysis. Recent success in the derivation of mouse haploid embryonic stem cells (haESCs) via parthenogenesis has enabled genetic screening in mammalian cells. However, successful generation of live animals from these haESCs, which is needed to extend the genetic analysis to the organism level, has not been achieved. Here, we report the derivation of haESCs from androgenetic blastocysts. These cells, designated as AG-haESCs, partially maintain paternal imprints, express classical ESC pluripotency markers, and contribute to various tissues, including the germline, upon injection into diploid blastocysts. Strikingly, live mice can be obtained upon injection of AG-haESCs into MII oocytes, and these mice bear haESC-carried genetic traits and develop into fertile adults. Furthermore, gene targeting via homologous recombination is feasible in the AG-haESCs. Our results demonstrate that AG-haESCs can be used as a genetically tractable fertilization agent for the production of live animals via injection into oocytes.

Long-term preservation of freeze-dried mouse spermatozoa

Many genetically engineered mice strains have been generated worldwide and sperm preservation is a valuable method for storing these strains as genetic resources. Freeze-drying is a useful sperm preservation method because it requires neither liquid nitrogen nor dry ice for preservation and transportation. We report here successful long-term preservation at 4 °C of mouse spermatozoa freeze-dried using a simple buffer solution (10mM Tris, 1mM EDTA, pH 8.0). Offspring with fertility were obtained from oocytes fertilized with freeze-dried spermatozoa from C57BL/6 and B6D2F1 mouse strains stored at 4 °C for 3 years. This freeze-drying method is a safe and economical tool for the biobanking of valuable mouse strains.

Cytochalasin B treatment of mouse oocytes during intracytoplasmic sperm injection (ICSI) increases embryo survival without impairment of development

Intracytoplasmic sperm injection (ICSI) is a technique commonly used in clinical and research settings. In mouse oocytes, conventional ICSI has a poor survival rate caused by a high level of lysis. Cytochalasin B (CB) is a toxic microfilament-inhibiting agent that is known to relax the cytoskeleton and enhance the flexibility of oocytes. CB has been used widely in nuclear transfer experiments to improve the success rate of the micromanipulation, however information describing the use of CB in ICSI is limited. Here, we demonstrated that the addition of 5 μg/ml CB to the manipulation medium of ICSI procedure significantly improved the survival rate of the ICSI embryos (80.74% vs. 89.50%, p < 0.05), and that there was no harm for the in vitro or in vivo development. The birth rates and birth weights were not significantly different between the CB-treated and -untreated groups. Interestingly, the microfilaments of the ICSI embryos were almost undetectable immediately after CB treatment; however, they gradually re-appeared and had fully recovered to the normal level 2 h later. Moreover, CB did not disturb spindle rotation, second polar body formation or pronuclei migration, and had no effect on the microtubules. We thus conclude that ICSI manipulation in CB-containing medium results in significantly improved survival rate of mouse ICSI embryos, and that short-term treatment with CB during ICSI manipulation does not have adverse effects on the development of ICSI embryos.

Cat fertilization by mouse sperm injection

Interspecies intracytoplasmic sperm injection has been carried out to understand species-specific differences in oocyte environments and sperm components during fertilization. While sperm aster organization during cat fertilization requires a paternally derived centriole, mouse and hamster fertilization occur within the maternal centrosomal components. To address the questions of where sperm aster assembly occurs and whether complete fertilization is achieved in cat oocytes by interspecies sperm, we studied the fertilization processes of cat oocytes following the injection of cat, mouse, or hamster sperm. Male and female pronuclear formations were not different in the cat oocytes at 6 h following cat, mouse or hamster sperm injection. Microtubule asters were seen in all oocytes following intracytoplasmic injection of cat, mouse or hamster sperm. Immunocytochemical staining with a histone H3-m2K9 antibody revealed that mouse sperm chromatin is incorporated normally with cat egg chromatin, and that the cat eggs fertilized with mouse sperm enter metaphase and become normal 2-cell stage embryos. These results suggest that sperm aster formation is maternally dependent, and that fertilization processes and cleavage occur in a non-species specific manner in cat oocytes.

Pre-treatment of sperm reduces success of ICSI in the pig

In pigs, although ICSI is a feasible fertilization technique, its efficiency is low. In general, injected pig sperm are insufficient to induce oocyte activation and embryonic development. Pretreatments for disrupting sperm membranes have been applied to improve the fertility of ICSI oocytes; however, we hypothesize that such pretreatment(s) may reduce the ability of the sperm to induce oocyte activation. We first evaluated the effects of sperm pretreatments (sonication (SO) to isolate the sperm heads from the tails, Triton X-100 (TX), and three cycles of repeated freezing/thawing (3×-FT) for disrupting sperm membranes) on the rate of pronucleus (PN) formation after ICSI. We found that oocytes injected with control (whole) sperm had higher rates of PN formation than those obtained after subjecting the sperm to SO, TX, and 3×-FT. The amounts of phospholipase Cζ (PLCζ), which is thought to be the oocyte-activating factor in mammalian sperm, in sperm treated by each method was significantly lower than that in whole untreated sperm. Furthermore, using immunofluorescence, it was found that in pig sperm, PLCζ was localized to both the post-acrosomal region and the tail area. Thus we demonstrated for the first time that sperm pretreatment leads to a reduction of oocyte-activating capacity. Our data also show that in addition to its expected localization to the sperm head, PLCζ is also localized in the tail of pig sperm, thus raising the possibility that injection of whole sperm may be required to attain successful activation in pigs.

Birth of normal mice following round spermatid injection without artificial oocyte activation

For fertilization using round spermatid injection (ROSI) in mice, oocytes need to be artificially preactivated because of the lack of oocyte-activating capacity in round spermatids of this species. However, when round spermatids were frozen-thawed before microinjection, 11-71% of injected oocytes developed into 2-cell embryos without any artificial activation. After being transferred into recipient females, 5-27% of these embryos reached term. At least some of the injected oocytes showed intracellular Ca(2+) oscillations, which normally occur after fertilization by mature spermatozoa. Thus, these round spermatids could transmit a sperm-borne oocyte-activating factor, which might have been released from spermatozoa and elongated spermatids in the same suspension by freezing and thawing. This possibility was further supported by activation of intact oocytes following transplantation of the pronuclei from ROSI-generated embryos. Thus, one-step ROSI can be achieved in mice simply by injecting frozen-thawed round spermatids into intact oocytes. Clearly, there is a need for careful interpretation of microinjection experiments when assessing the oocyte-activating capacity of spermatogenic cells, especially when they are derived from frozen-thawed stocks.

What to do when ICSI fails

The refinement of gamete micromanipulation techniques has made conception possible for couples with male factor infertility who otherwise would remain childless. Moreover, intracytoplasmic sperm injection (ICSI) has ensured that such refractory cases can now generate offspring as successfully as in couples that merely require in vitro insemination. However, despite the now sterling record of ICSI it does not assure a successful outcome for every patient. This can be due, for instance, to the inability of the spermatozoon to activate the oocyte, and applies obviously in cases where spermatozoa are absent from the ejaculate or testicular biopsy. In the present paper we describe in detail the reasons for such failure and review the options that may help overcome it. In particular, we outline the treatment protocol for the situation in which spermatozoa are unable to induce oocyte activation. Further, we report on the clinical outcome achieved with spermatozoa retrieved from the testis, and in cases of extreme oligozoospermia we also explore the option of replicating a single spermatozoon while gaining information on its genomic content. For the most extreme situation in which men have no identifiable germ cells, we will discuss the current status of efforts to accomplish neo-gametogenesis through embryonic stem cell differentiation.

DNA synthesis and epigenetic modification during mouse oocyte fertilization by human or hamster sperm injection

PURPOSE

To evaluate DNA synthesis and epigenetic modification in mouse oocytes during the first cell cycle following the injection of human or hamster sperm.

METHODS

Mouse oocytes following the injection of human and hamster sperm and cultured in M16 medium.

RESULTS

Male and female pronucleus formation, DNA synthesis, histone protein modification, and heterochromatin formation were similar in mouse oocytes injected with human or hamster sperm. However, DNA methylation patterns were altered in mouse oocytes following human sperm injection. Immunocytochemical staining with a histone H3-MeK9 antibody revealed that human and hamster sperm chromatin associated normally with female mouse chromatin, then entered into the metaphase and formed normal, two-cell stage embryos.

CONCLUSIONS

Although differences in epigenetic modification of DNA were observed, fertilization and cleavage occurred in a species non-specific manner in mouse oocytes.

Geometric Characterization of Cell Membrane of Mouse Oocytes for ICSI

Intracytoplasmic sperm injection (ICSI) is a broadly utilized assisted reproductive technology. A number of technologies for this procedure have evolved lately, such as the most commonly utilized piezo-assisted ICSI technique (P-ICSI). An important problem with this technique, however, is that it requires a small amount of mercury to stabilize the tip of the penetration micropipette. A completely different and mercury-free injection technology, called the rotationally oscillating drill (Ros-Drill©) (RD-ICSI), was recently developed. It uses microprocessor-controlled rotational oscillations of a spiked micropipette after the pipette deforms the membrane to a certain tension level. Inappropriate selection of this initiation instant typically results in cell damage, which ultimately leads to unsuccessful ICSI. During earlier manual clinical tests of Ros-Drill, the technicians’ expertise determined this instant in an ad hoc fashion. In this paper, we introduce a computer-vision-based tool to mechanize this process with the objective of maintaining the repeatability and introducing potential automation. Computer images are used for monitoring the membrane deformations and curvature variations as the basis for decision making. The main contribution of this paper is in the specifics of the computer logic to perform the monitoring. These new tools are expected to provide a practicable means for automating the Ros-Drill-assisted ICSI operation.

The effect on intracytoplasmic sperm injection outcome of genotype, male germ cell stage and freeze-thawing in mice

Background

Intracytoplasmic sperm injection (ICSI) has been widely used to study the mechanisms of mammalian fertilization and to rescue male-factor infertility in humans and animals. However, very few systematic analyses have been conducted to define factors affecting the efficiency of ICSI. In this study, we undertook a large-scale series of ICSI experiments in mice to define the factors that might affect outcomes.

Methodology/Principal Findings

We used a 5×3×2 factorial design with the following factors: mouse genotype (ICR, C57BL/6, DBA/2, C3H/He, and 129/Sv strains), type of male germ cells (epididymal sperm, elongated or round spermatids), and their freeze–thawing treatment. The efficiencies (parameters) of each developmental step were analyzed by three-way ANOVA (significance level P<0.01). The type of male germ cells affected all the four parameters observed: oocyte survival after injection, cleavage of oocytes, implantation, and birth of offspring. Genotype affected the oocyte survival, cleavage and birth rates, whereas freeze–thawing had no effects on any of the parameters. There were significant genotype/cell type interactions for oocyte survival and cleavage, indicating that they were determined by a combination of strain and germ cell maturity. Multiple comparisons revealed that spermatozoa and elongated spermatids gave better implantation and birth rates than did round spermatids, while spermatozoa and elongated spermatozoa were indistinguishable in their ability to support embryonic development. The best overall efficiency (birth rate per oocytes injected) was obtained with frozen–thawed DBA/2 strain elongated spermatids (23.2±4.2%).

Conclusions/Significance

The present study provides the first comprehensive information on ICSI using the mouse as a model and will contribute to the efficient use of materials, time, and efforts in biomedical research and clinics involving ICSI.

Medaka fish stem cells and their applications

Stem cells are present in developing embryos and adult tissues of multicellular organisms. Owing to their unique features, stem cells provide excellent opportunities for experimental analyses of basic developmental processes such as pluripotency control and cell fate decision and for regenerative medicine by stem cell-based therapy. Stem cell cultures have been best studied in 3 vertebrate organisms. These are the mouse, human and a small laboratory fish called medaka. Specifically, medaka has given rise to the first embryonic stem (ES) cells besides the mouse, the first adult testis-derived male stem cells spermatogonia capable of test-tube sperm production, and most recently, even haploid ES cells capable of producing Holly, a semi-cloned fertile female medaka from a mosaic oocyte created by microinjecting a haploid ES cell nucleus directly into a normal oocyte. These breakthroughs make medaka a favoring vertebrate model for stem cell research, the topic of this review.

Glucose parameters are altered in mouse offspring produced by assisted reproductive technologies and somatic cell nuclear transfer

Fortunately, the majority of children conceived through assisted reproductive technologies (ARTs) appear healthy; however, metabolic abnormalities, including elevated glucose and increased and altered adipose tissue deposition, have been reported in adolescents. To parse out factors that may be responsible, we investigated the effects of two different ARTs--in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI)--as well as somatic cell nuclear transfer (SCNT) on glucose clearance, body weight, and body composition of young adult mice. Female and male mice generated through ART weighed more than control (naturally conceived [STOCK]) mice at birth. No differences in body weight were observed in males up to 8 wk of age. ART females took longer than control mice to clear a glucose bolus, with glucose clearance most impaired in SCNT females. IVF females secreted more insulin and had a higher insulin peak 15 min after glucose injection compared with all other groups. Male mice exhibited no differences in glucose clearance, but IVF males required more insulin to do so. SCNT females weighed more than IVF, ICSI, and STOCK females, and they had higher fat content than ICSI females and higher leptin levels than all other groups. These results show that glucose parameters are altered in young adult mice conceived through techniques associated with ART before onset of obesity and may be responsible for its development later in life. The present study suggests that more investigation regarding the long-term effects of manipulations associated with ART is warranted.

Kinetics of human male pronuclear development in a heterologous ICSI model

PURPOSE

To evaluate human sperm nuclear chromatin decondensation in a heterologous ICSI system using hamster ova injected with human sperm.

MATERIALS AND METHODS

Frozen hamster oocytes were injected with Triton X-100 treated sperm and fixed at different time points post ICSI. Oocytes injected with non-treated sperm served as controls. Male pronuclear decondensation was evaluated after staining with DAPI.

RESULTS

Sperm cells with partially destroyed membranes and depletion of the acrosome decondense more rapidly and to a greater extent than membrane/acrosome intact cells. Marked variability in pronuclear size was observed for any time point post ICSI, which most probably reflects the heterogeneity in the mature human sperm population.

CONCLUSION

Remodeling of male gamete nuclei in this heterologous ICSI mimics events that occur during natural fertilization in humans and therefore this approach may be used for studies of human sperm chromosomes transformations.

Fertilizability, developmental competence, and chromosomal integrity of oocytes microinjected with pre-treated spermatozoa in mice

The aim of the present study was to investigate the safety of sperm pre-treatment during the ICSI procedure using a mouse model. Mouse spermatozoa were treated with methyl-β-cyclodextrin, lysolecithin, Triton X-100, and dithiothreitol (DTT), and injected into mouse oocytes. The injected oocytes were monitored for chromosomal integrity and pre- and post-implantation development. The chromosomal integrity of the injected oocytes was impaired by in vitro incubation and chemical antagonism. Particularly in the 60-min DTT group, severe chromosome damage increased. Despite the chromosomal damage, the resultant embryos frequently developed to the blastocyst stage. However, the embryos in the 60-min DTT group had significantly higher chromosomal damage and decreased developmental competence to live fetuses. These results indicate that excessive sperm pre-treatment such as DTT for 60 min generates severe chromosome damage in injected oocytes, and that the damage decreases developmental competence to live fetuses but not to blastocysts.

Medaka haploid embryonic stem cells

The appearance of diploidy, the presence of two genomes or chromosome sets, is a fundamental hallmark of eukaryotic evolution and bisexual reproduction, because diploidy offers the basis for the bisexual life cycle, allowing for oscillation between diploid and haploid phases. Meiosis produces haploid gametes. At fertilization, male and female gametes fuse to restore diploidy in a zygote, which develops into a new life. At sex maturation, diploid cells enter into meiosis, culminating in the production of haploid gametes. Therefore, diploidy ensures pluripotency, cell proliferation, and functions, whereas haploidy is restricted only to the post-meiotic gamete phase of germline development and represents the end point of cell growth. Diploidy is advantageous for evolution. Haploidy is ideal for genetic analyses, because any recessive mutations of essential genes will show a clear phenotype in the absence of a second gene copy. Recently, my laboratory succeeded in the generation of medaka haploid embryonic stem (ES) cells capable of whole animal production. Therefore, haploidy in a vertebrate is able to support stable cell culture and pluripotency. This finding anticipates the possibility to generate haploid ES cells in other vertebrate species such as zebrafish. These medaka haploid ES cells elegantly combine haploidy and pluripotency, offering a unique yeast-like system for in vitro genetic analyses of molecular, cellular, and developmental events in various cell lineages. This chapter is aimed to describe the strategy of haploid ES cell derivation and their characteristics, and illustrate the perspectives of haploid ES cells for infertility treatment, genetic screens, and analyses.

Generation of medaka fish haploid embryonic stem cells

Haploid embryonic stem (ES) cells combine haploidy and pluripotency, enabling direct genetic analyses of recessive phenotypes in vertebrate cells. Haploid cells have been elusive for culture, due to their inferior growth and genomic instability. Here, we generated gynogenetic medaka embryos and obtained three haploid ES cell lines that retained pluripotency and competitive growth. Upon nuclear transfer into unfertilized oocytes, the haploid ES cells, even after genetic engineering, generated viable offspring capable of germline transmission. Hence, haploid medaka ES cells stably maintain normal growth, pluripotency, and genomic integrity. Mosaic oocytes created by combining a mitotic nucleus and a meiotic nucleus can generate fertile fish offspring. Haploid ES cells may offer a yeast-like system for analyzing recessive phenotypes in numerous cell lineages of vertebrates in vitro.

An efficient method for generating transgenic mice using NaOH-treated spermatozoa

Transgenic (Tg) animals are widely used in researching the characteristics of exogenous genes. Intracytoplasmic sperm injection (ICSI)-mediated transgenesis (ICSI-Tr) has been a useful method for generating Tg animals, especially in the mouse. However, the original methods using freeze-thawed spermatozoa showed severe chromosomal damage and low offspring rates after embryo transfer. Herein, we describe an improved method to generate Tg mice efficiently using a simple pretreatment of spermatozoa with 10 mM NaOH. These spermatozoa lost their plasma membrane and tail, while still maintaining nuclear integrity. Sperm heads were mixed with 0.5-5 ng/microl of the transgene for enhanced green fluorescent protein (EGFP) for 3 min to 1 h at room temperature and were then microinjected into oocytes by ICSI. The best results were obtained when treated spermatozoa were incubated with 2 ng/microl of EGFP for 10 min; 55.6% of injected embryos developed to the blastocyst stage, and more than half (56.9%) of them displayed EGFP fluorescence. Under these conditions, 12 pups of 34 offspring were positive for the transgene after transfer at the 2-cell stage into pseudopregnant recipient mice (a high rate [10.2%] from manipulated embryos). This method was found to be suitable for hybrid and inbred strains of mouse such as C57BL/6 and 129X1/Sv. Thus, a simple sperm pretreatment with NaOH before ICSI-Tr resulted in an efficient insertion of an exogenous gene into the host genome. This method allows for easy production of Tg mice, requiring fewer oocytes for micromanipulation than classical methods.

The role of centrosomes in mammalian fertilization and its significance for ICSI

Centrosome integrity is critically important for successful fertilization and embryo development. In humans, the sperm contributes the dominant centrosomal material containing centrioles and centrosomal components onto which oocyte centrosomal proteins assemble after sperm incorporation to form the sperm aster that is essential for uniting sperm and oocyte pronuclei. Increasingly, dysfunctional sperm centrosomes have been identified as a factor for sperm-derived infertility and heterologous Intracytoplasmic Sperm Injection (ICSI) has been used to assess centrosome and sperm aster formation and clearly established a relationship between infertility and sperm centrosomal dysfunction. ICSI has been used successfully to provide novel treatment to overcome male factor infertility and it may open up new possibilities to correct specific sperm-related centrosome dysfunctions at molecular levels. New data indicate that it is now possible to replace dysfunctional centrosomes with functional donor sperm centrosomes which may provide new treatment for couples in which infertility is a result of centrosome-related sperm dysfunctions.

Possible causal factors of structural chromosome aberrations in intracytoplasmic sperm injection of the mouse

Incidence of structural chromosome aberrations in mouse one-cell embryos produced by intracytoplasmic sperm injection (ICSI) with mature epididymal spermatozoa were influenced by sperm incubation medium and time. When spermatozoa were incubated in bicarbonate-buffered TYH for ≤0.5 h, the embryo aberration rates were significantly higher than in vitro fertilization (IVF) embryos. However, after the incubation of spermatozoa in the same medium for ≥2 h, the aberration rates were close to the IVF embryo level. When spermatozoa were incubated in bicarbonate-buffered mCZB, hepes-buffered H-TYH and H-mCZB, and phosphate-buffered PB1, the increased incidences of aberrations were observed at any incubation time. In the case of sperm incubation in H-TYH, H-mCZB and PB1, the aberration rates increased in a time-dependent manner. Chromosome aberrations generated by ICSI were transmissible to offspring. On the other hand, the aberration rate in embryos derived from testicular spermatozoa was independent of the medium type and incubation time. Thus, the incubation media appears to have no effect on sperm chromatin. TYH can effectively induce capacitation and acrosome reaction, while H-TYH, H-mCZB and PB1 never induce these spermatozoal events. It is probable that the cholesterol-rich plasma membrane and intact acrosome injected into the ooplasm affect sperm chromatin remodeling, thus resulting in the generation of chromosome damage in ICSI embryos.

Assessment of three generations of mice derived by ICSI using freeze-dried sperm

Although the derivation of mice by intracytoplasmic sperm injection (ICSI) using freeze-dried sperm has been demonstrated previously, a comprehensive analysis of their viability, health, and fertility has not. The purpose of the present study was to determine the extent to which ICSI using freeze-dried sperm stored at 4 degrees C for 1-2 months from mice on either an inbred (C57BL/6J) or hybrid (B6D2F1/J) genetic background results in genomic instability and/or phenotypic abnormality in mice and two generations of their progeny. Fertilization rates (number of 2-cells per injected oocytes) using ICSI of fresh and freeze-dried sperm were similar within and between mouse strains, although fewer freeze-dried sperm-derived embryos than fresh sperm-derived embryos developed to blastocysts in vitro (C57BL/6J and B6D2F1/J) and liveborn pups in vivo (B6D2F1/J only). Nevertheless, once born, mice derived by ICSI using freeze-dried sperm in both mouse strains were healthy and reproductively sound. No major differences in litter size, weaning rate, and sex ratio were noted in the two generations of progeny (F2 and F3) of ICSI-derived offspring using freeze-dried sperm compared with that in the natural mating (control) group. Further, there was no evidence that either ICSI or freeze drying induced genomic instability, as determined by microsatellite analysis of the derived mice and subsequent generations when compared with both parental genotypes, nor were there differences in the number or types of pathological changes in any of the three generations of progeny. We conclude that viable, healthy and genomically stable mice can be derived by ICSI using freeze-dried mouse sperm stored in the refrigerator for at least 2 months. Further, because freeze drying is a simpler and more economical technique compared with embryo and sperm cryopreservation, the results of this study justify additional research to continue to develop and enhance the technique for the preservation, storage, and sharing of genetically altered mice.

Production of normal mice from spermatozoa denatured with high alkali treatment before ICSI

In mammals, ICSI is now a very important tool for both assisted reproductive technology and studying the mechanisms of fertilization. In the latter experiments, it is important to use spermatozoa that have lost their oocyte activation capacity but still retain their developmental potential. In this study, we used high-concentration NaOH to remove oocyte activation potential from spermatozoa, and examined whether normal offspring could be generated from these spermatozoa after ICSI. The spermatozoa were treated with different concentrations of NaOH (1–100 mM) for 1 h and then neutralized with equal amounts of same concentration of HCl. In 10 mM NaOH-treated spermatozoa, the cell membrane was broken and most of them failed to activate oocytes after their injection into the oocytes. However, these spermatozoa did not show strong damage, and after artificial activation with SrCl2, all of the zygotes were judged as normal by immunostaining to check the methylation status of histone H3 lysine 9, low chromosome damage by karyotype assay and staining with DNA double-strand breaks marker, γH2AX. Moreover, after transferring those embryos into recipient females, 106 (36.7%) live and healthy offspring were delivered, which is similar to the rate in the fresh control group. By contrast, spermatozoa treated with lower NaOH concentrations retained their oocyte activation capacity and those treated with higher concentrations lost their developmental potential. This suggests that 10 mM NaOH for 1 h is the best treatment to completely destroy the cell membrane and activation capacity of spermatozoa without injuring their developmental potential.

The oocyte activation and Ca2+ oscillation-inducing abilities of mouse and human dead (sonicated) spermatozoa

In ICSI procedures, it is well known that the selection of viable (live) spermatozoa and certain types of immobilization prior to injection is very important for obtaining successful results, but unfortunately there are rare situations when only immotile spermatozoa are available (such as in severe asthenozoospermia or necrozoospermia). In such cases, failure of oocyte activation after ICSI often occurs and may be due to the lack of SOAF (sperm-borne oocyte activating factor) activity. In order to investigate the SOAF activities of dead spermatozoa, mouse and human spermatozoa were immobilized (killed by sonication), maintained in THF medium for varying time intervals (up to 72 h) and then injected into mature unfertilized mouse oocytes. Injected mouse oocytes were examined for their activation, development into blastocysts and Ca2+ responses by imaging and confocal laser scanning microscope. The rates of oocyte activation, blastocyst development and normal patterns of Ca2+ oscillation from the killed-sperm-injected oocytes decreased gradually in accordance with the maintenance interval between sonication and injection. For injection with mouse sonicated spermatozoa, the rate of normal Ca2+ oscillations declined first (after a 3 h maintenance interval) and then blastocyst development was gradually obstructed (after approx. 10 h). The oocyte activation-inducing ability of dead spermatozoa was maintained for a relatively long period, but began to decline after 20 h. The activation rates and Ca2+ response of the oocytes that were injected with human sonicated spermatozoa decreased earlier than those injected with mouse spermatozoa. Although the oocyte activation-inducing ability was maintained for a relatively long time after the death of the spermatozoa, embryo development into blastocysts and the rate of normal Ca2+ oscillations declined after a short maintenance interval between sonication and injection. The Ca2+ response seemed to be the most sensitive indicator for the evaluating the SOAF activity of dead (killed) spermatozoa.

Use of intracytoplasmic sperm injection (ICSI) to generate transgenic animals

Even though intracytoplasmic sperm injection (ICSI) has been widely used for the production of offspring in human infertility clinics and in reproductive research laboratories using mice, many researchers engaged in animal transgenesis still consider it somewhat cumbersome. The greatest advantage of ICSI-mediated transgenesis is that it allows introduction of very large DNA transgenes (e.g., yeast artificial chromosomes), with relatively high efficiency into the genomes of hosts, as compared to pronuclear injection. Recently, we have developed an active form of intracytoplasmic sperm injection-mediated transgenesis (ICSI-Tr) with fresh sperm utilizing transposons. The transgenic efficiencies rival all transgenic techniques except that of lentiviral methods.

Presence and release of bovine sperm histone H1 during chromatin decondensation by heparin-glutathione

During spermatogenesis, changes in sperm nuclear morphology are associated with the replacement of core somatic histones by protamines. Although protamines are the major nucleoproteins of mature sperm, not all species totally replace the histones. Histone H1, along with protamines, mediates chromatin condensation into an insoluble complex that is transcriptionally inactive. In vitro, heparin-reduced glutathione causes sperm decondensation, and the structures formed are morphologically similar to the in vivo male pronucleus. To study the participation of histone H1 in bovine sperm chromatin remodelling, we measured the presence and release of histone H1 by immunofluorescence, acetic acid-urea-triton-polyacrylamide gel electrophoresis, and immunoblotting. Nuclear decondensation was induced by 80 microM heparin and 15.0 mM reduced glutathione (GSH) for 7, 14, and 21 h at 37 degrees C. Additionally, nucleons, composed of nuclei isolated from the sperm, were decondensed with 20.0 microM heparin and 5.0 mM GSH for 4.0 h at 37 degrees C. Controls were incubated in buffer for similar periods of time. Immunofluorescent localization of histone H1 was carried out with mouse monoclonal antibody, and DNA localization was visualized by 0.001% quinacrine staining. Chromatin decondensation was accompanied by increased sperm nuclei and nucleon surface area. We observed that histone H1 was localized exclusively in the nuclei of intact sperm and nucleons. Histone H1 immunofluorescent intensity did not change in control samples but decreased over time in samples treated with heparin-GSH. There was a negative correlation between the surface area of sperm nuclei and immunohistochemical intensity of histone H1 (P < 0.05). Nucleon decondensation showed a similar relationship. By electrophoresis and immunoblotting, we verified the loss of histone H1 from the sperm and nucleons and its release into the incubation media. Based on these results, we propose that histone H1 is present in the bovine sperm nuclei. H1 depletion may participate in chromatin decondensation and nuclear swelling induced by heparin-GSH.

Rotationally oscillating drill (Ros-Drill) for mouse ICSI without using mercury

Intracytoplasmic sperm injection (ICSI) is an important assisted reproductive technology (ART). Due to deployment difficulties and low efficiency of the earlier (conventional) version of ICSI, especially in the mouse, a piezo-assisted ICSI technique had evolved as a popular ART methodology in recent years. An important and remaining problem with this technique, however, is that it requires small amounts of mercury to stabilize the pipette tip when piezoelectric force pulses are applied. To eliminate this problem we developed and tested a completely different and mercury-free technology, called the "Ros-Drill" (rotationally oscillating drill). The technique uses microprocessor-controlled rotational oscillations on a spiked micropipette without mercury or piezo. Preliminary experimental results show that this new microinjection technology gives high survival rate (>70% of the injected oocytes) and fertilization rate (>80% of the survived oocytes), and blastocyst formation rates in early trials (approximately 50% of the survived oocytes). Blastocysts created by Ros-Drill ICSI were transferred into the uteruses of pseudopregnant surrogate mothers and healthy pups were born and weaned. The Ros-Drill ICSI technique is automated and therefore; it requires a very short preliminary training for the specialists, as evidenced in many successful biological trials. These advantages of Ros-Drill ICSI over conventional and piezo-assisted ICSI are clearly demonstrated and it appears to have resolved an important problem in reproductive biology.

Biofluid mechanics of the human reproductive process: modelling of the complex interaction and pathway to the oocytes

Recent revelations in the human reproductive process have fuelled much interest in this field of study. In particular, the once prevailing view of large numbers of ejaculated sperms racing towards the egg has been refuted recently. This is opposed to the current views derived from numerous clinical findings that state that only a very small number of sperms will ever enter the oviduct. It is believed that these few sperms must have been guided to make the long, tedious and obstructed journey to the egg. For a mature spermatozoon, its hyperactivated swimming motility upon capacitation plays an important role in the fertilization of a mature egg. Likewise, the female genital tract also provides guiding mechanisms to complement the survival of normal hydrodynamic profile sperms and thus promotes an eventual sperm–egg interaction. Understanding these mechanisms can be essential for the derivation of assisted conception techniques especially those in vitro. With the aid of computational models and simulation, suitability and effectiveness of novel assisted conception methodology can be assessed, particularly for those yet to be ready for clinical trials. This review discusses the possible bioengineering models and the mechanisms by which human spermatozoa are guided to the egg.