Euthanasia via CO2 inhalation causes premature cortical granule exocytosis in mouse oocytes and influences in vitro fertilization and embryo development

Generation of high quality mouse metaphase II oocytes is an integral part for efficient in vitro fertilization (IVF), and subsequent embryo production for reproductive studies and genome banking. The main objectives of this study were to investigate the impact of various euthanasia methods on IVF, embryo development, and subcellular structures of MII mouse oocytes. Following superovulation regimen, female mice were euthanized by high flow CO₂ (H CO₂ ), low flow CO₂ (L CO₂ ), or cervical dislocation (CD). The MII oocytes obtained from these mice were evaluated for subcellular integrity by assessing their cortical granules and F-actin. Furthermore, fertilization and subsequent embryonic development competence up to blastocyst stage were also evaluated in vitro. The oocytes collected from females euthanized by CD resulted in significantly higher two-cell development rates (p = 0.028) and subsequently lead to in higher embryo development rates (p = 0.027) compared with oocytes from females euthanized by L CO₂ . The cortical granule integrity analysis revealed significantly higher rate of premature cortical granules exocytosis (PCGE) for L CO₂ group compared with CD and H CO₂ groups (p < 0.001). These data collectively suggest that CO₂ associated PCGE during euthanasia procedure is the main cause of decreased IVF rates and CD is the optimal euthanasia method for the purpose of obtaining good quality MII oocytes for mouse IVF and other reproductive studies.

Intergenerational transmission of the positive effects of physical exercise on brain and cognition

Physical exercise has positive effects on cognition, but very little is known about the inheritance of these effects to sedentary offspring and the mechanisms involved. Here, we use a patrilineal design in mice to test the transmission of effects from the same father (before or after training) and from different fathers to compare sedentary- and runner-father progenies. Behavioral, stereological, and whole-genome sequence analyses reveal that paternal cognition improvement is inherited by the offspring, along with increased adult neurogenesis, greater mitochondrial citrate synthase activity, and modulation of the adult hippocampal gene expression profile. These results demonstrate the inheritance of exercise-induced cognition enhancement through the germline, pointing to paternal physical activity as a direct factor driving offspring's brain physiology and cognitive behavior.

Preclinical evaluation of a new cryopreservation container for a limited number of human spermatozoa

The aim of this study was to develop a new container for cryopreservation of a limited number of spermatozoa. To evaluate the efficacy and safety of this new container, we performed preclinical evaluations using human sperm or mouse oocytes and sperm. First, using human sperm that was frozen and then thawed, we demonstrated that the sperm recovery rate using the new container was 96.7% (58/60), which was significantly higher (P < 0.05) than the recovery rate of 21.2% (11/52) when using the Cryotop^®. Sperm motility rates were 19.2% (10/52) using the Cryotop^® and 35.0% (21/60) using the new container. Second, murine epididymal spermatozoa were divided into three groups: fresh spermatozoa, spermatozoa frozen using a straw, and spermatozoa frozen using the new container. Sperm motility, sperm membrane and DNA integrity, in vitro development of fertilized eggs, and offspring development after embryo transfer were assessed. The motility of freeze-thawed sperm was lower in spermatozoa that were frozen using the new container than in fresh spermatozoa or those that were frozen using a straw. After intracytoplasmic sperm injection, the survival rate was 96.7% (145/150), the 2-cell development rate was 90.3% (131/145), and the blastocyst development rate was 77.2% (112/145), when using the new container. There were no differences in the sperm membrane, DNA integrity, or in the embryo development rates to the blastocyst stage among the different frozen groups. Six offspring were derived from spermatozoa freeze-thawed in the new container, and they developed normally. Thus, the new container allows easy handling of a small number of sperms and minimizes sperm loss during cryopreservation.

Cryopreservation disrupts lipid rafts and heat shock proteins in yellow catfish sperm

Lipid rafts and associated membrane proteins (flotillin, caveolin) play important roles in cell signaling and sperm fertilization while heat shock proteins (Hsp) ensure properly protein folding to fulfill their physiological functions. The markedly reduced fertility in thawed sperm after cryopreservation could result from disrupted membrane lipid rafts and these proteins. To explore the effect of sperm cryopreservation on lipid rafts and heat shock proteins, we compared lipid raft integrity, and the expression levels of lipid raft associated proteins (Flot-1, Flot-2, Cav-1) as well as heat shock proteins (Hsp90, Hsp70) in fresh and thawed sperm cryopreserved under different scenarios in yellow catfish. We found higher lipid raft integrity, higher protein expression levels of Flot-1, Flot-2, Cav-1, Hsp90, and Hsp70 in fresh sperm samples than in thawed sperm samples, in thawed sperm samples cryopreserved with optimal cooling rate than those cryopreserved with sub-optimal cooling rate, and in thawed sperm samples cryopreserved with extenders supplemented with cholesterol than those supplemented with methyl-β-cyclodextrin (for cholesterol removal). Our findings indicate that lipid raft integrity, and expression levels of Flot-1, Flot-2, Cav-1, Hsp90, and Hsp70 are clearly associated with sperm quality, and together they may play a cumulative role in reduced fertility associated with thawed sperm in aquatic species.

Dimethyl sulfoxide and quercetin prolong the survival, motility, and fertility of cold-stored mouse sperm for 10 days

Technology for preserving sperm is useful for disseminating valuable male genetic traits. Cold storage is suitable for easily transporting sperm as an alternative to the shipment of live animals. However, there is a technical limitation in that the fertility of cold-stored sperm declines within 3 days. To overcome this problem, we examined the protective effects of quercetin and dimethyl sulfoxide (DMSO). DMSO and quercetin maintained the fertility and motility of cold-stored sperm for 10 days. In addition, quercetin attenuated the reduction of mitochondrial membrane potential of cold-stored sperm during sperm preincubation, allowing the induction of capacitation, and it localized to the midpiece of sperm. Furthermore, DMSO and quercetin enhanced the level of tyrosine phosphorylation of cold-stored sperm. DMSO and quercetin have life-prolonging effects on sperm during cold storage. Cold storage using DMSO and quercetin will provide a robust system for internationally transporting valuable sperm samples.

MRL/MpJ mice produce more oocytes and exhibit impaired fertilisation and accelerated luteinisation after superovulation treatment

MRL/MpJ mice exhibit distinct phenotypes in several biological processes, including wound healing. Herein we report two unique phenotypes in the female reproductive system of MRL/MpJ mice that affect ovulation and luteinisation. We found that superovulation treatment resulted in the production of significantly more oocytes in MRL/MpJ than C57BL/6 mice (71.0±13.4 vs 26.8±2.8 respectively). However, no exon mutations were detected in genes coding for female reproductive hormones or their receptors in MRL/MpJ mice. In addition, the fertilisation rate was lower for ovulated oocytes from MRL/MpJ than C57BL/6 mice, with most of the fertilised oocytes showing abnormal morphology, characterised by deformation and cytolysis. Histological tracing of luteinisation showed that MRL/MpJ mice formed corpora lutea within 36h after ovulation, whereas C57BL/6 mice were still at the corpora haemorrhagica formation stage after 36h. The balance between the expression of matrix metalloproteinases and their tissue inhibitors shifted towards the former earlier after ovulation in MRL/MpJ than C57BL/6 mice. This result indicates a possible link between accelerated extracellular matrix remodelling in the ovulated or ruptured follicles and luteinisation in MRL/MpJ mice. Together, these findings reveal novel phenotypes in MRL/MpJ mice that provide novel insights into reproductive biology.

The CARD Method for Mouse Sperm Cryopreservation and In Vitro Fertilization Using Frozen-Thawed Sperm

In the last few years sperm cryopreservation was rapidly established as the technique to efficiently manage production, preservation, and transportation of genetically engineered mice. However, occasionally, the reduced fertility of the frozen-thawed mouse sperm can make it difficult to revitalize the mouse by in vitro fertilization (IVF). In particular, the frozen-thawed sperm of C57BL/6 mice, widely used as the background of choice for genetically engineered strains, show very low fertility after freezing and thawing. To overcome this problem, we have developed a new protocol for sperm cryopreservation and IVF with frozen-thawed C57BL/6 sperm as well as other mouse strains. This protocol has the following three modifications: (1) addition of L-glutamine to the sperm cryoprotectant, (2) addition of methyl-β-cyclodextrin to the sperm preincubation medium, and (3) addition of reduced glutathione to the fertilization medium. These modifications greatly enhanced the fertility of frozen-thawed C57BL/6 sperm, resulting in a stable fertilization rate >80% in IVF. Our results indicate that this robust protocol for sperm cryopreservation may improve the archiving and distributing system for genetically engineered mice.

Effect of Lepidium meyenii on in vitro fertilization via improvement in acrosome reaction and motility of mouse and human sperm

PURPOSE

The direct effects of Lepidium meyenii (Maca) on sperm remain unclear. Herein, we examined the direct effect of Maca on in vitro fertilization.

METHODS

We examined the fertilization rate in a mouse model and the rate of acrosome reaction in sperm from transgenic mice expressing enhanced green fluorescent protein (EGFP) in a Maca extract-containing human tubal fluid (HTF) medium. Using human sperm, we assessed acrosome status via fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA) staining and performed detailed analysis using a sperm motility analysis system (SMAS).

RESULTS

In the mouse model, the fertilization rate in the Maca extract-containing HTF was significantly higher than that in the control medium. The acrosome reaction rate in sperm from transgenic mice expressing EGFP was also significantly higher in the Maca extract-containing HTF than that in the control medium. Similarly, a high acrosome reaction rate, identified via FITC-PNA staining of human sperm samples, was found in the Maca extract-containing HTF compared with that in the control medium. Human sperm motility in the Maca extract-containing HTF was also increased compared with that in the control medium as measured using an SMAS.

CONCLUSIONS

Maca improved in vitro fertilization rates by inducing an acrosome reaction and increasing sperm motility.

Risk of chromosomal aberration in spermatozoa during intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) has become critical for the treatment of severe male infertility. The principal feature of ICSI is the direct injection of spermatozoon into an oocyte, which facilitates the production of fertilized embryos regardless of semen characteristics, such as sperm concentration and motility. However, the chromosomal integrity of ICSI zygotes is degraded compared to that of zygotes obtained via in vitro fertilization. This chromosomal damage may occur due to the injection of non-capacitated, acrosome-intact spermatozoa, which never enter the oocytes under natural fertilization. Furthermore, it is possible that the in vitro incubation and pre-treatment of spermatozoa during ICSI results in DNA damage. Chromosomal aberrations in embryos induce early pregnancy losses. However, these issues may be overcome by embryo production using gametes with guaranteed chromosomal integrity. Because conventional chromosome analysis requires fixing cells to obtain the chromosome spreads, embryos cannot be produced using the nucleus that has been analyzed. On the other hand, genome cloning using androgenic or gynogenic embryos provides an additional nucleus for chromosome analysis following embryo production. Thus, this review aims to highlight the hazardous nature of chromosomal aberrations in sperm during ICSI and to introduce a method for the prezygotic examination for chromosomal aberrations.

Electroporation-mediated genome editing in vitrified/warmed mouse zygotes created by IVF via ultra-superovulation

Recently, genome editing in mouse zygotes has become convenient and scalable, in association with various technological developments and improvements such as novel nuclease tools, alternative delivery methods, and contemporary reproductive engineering techniques. We have so far demonstrated the applicability of ultra-superovulation, in vitro fertilization (IVF), and vitrification/warming of zygotes in microinjection-mediated mouse genome editing. Moreover, an electroporation-mediated method has rapidly become established for simple gene knockout and small precise modifications including single amino acid substitutions. Here, we present an updated example of an application coupling the following three latest technologies: 1) CRISPR-Cas9 ribonucleoprotein as the most convenient genome-editing reagent, 2) electroporation as the most effortless delivery method, and 3) cryopreserved oocytes created by IVF via ultra-superovulation as the most animal welfare- and user-friendly strategy. We successfully created gene knockout and knock-in mice carrying insertion/deletion mutations and single amino acid substitutions, respectively, using the streamlined production system of mouse genome editing described above, referred to as the CREATRE (CARD-based Reproductive Engineering-Assisted Technology for RNP Electroporation) system. Owing to its accessibility, robustness, and high efficiency, we believe that our CREATRE protocol will become widely used globally for the production of genome-edited mice.

A new, simple and efficient liquid nitrogen free method to cryopreserve mouse spermatozoa at -80 °C

The mouse is widely used for biomedical research and an increasing number of genetically altered models are currently generated, therefore centralized repositories are essentials to secure the important mouse strains that have been developed. We have previously reported that spermatozoa of wild type and mutant strains frozen using standard laboratory protocols can be transported in dry ice (-79 °C) for 7 days and safely stored in a -80 °C freezer for up to two years. The objective of this new study was to compare the effects of the freezing techniques using LN₂ or -80 °C freezer on fertility of frozen-thawed mouse spermatozoa. After thawing, sperm fertility was comparable (P > 0,05) between the LN₂ and the -80 °C samples for at least 1 year. Furthermore, we showed that it is possible to freeze and store mouse semen directly at -80 °C and eventually transfer it to LN₂ irrespective of storage time. This study is relevant because it shows for the first time that mouse spermatozoa can be efficiently frozen and stored at -80 °C with no use of liquid nitrogen for a long period of time. A new, simple, efficient and flexible, liquid nitrogen free, method was developed for freezing and maintaining spermatozoa of wild type and mutant C57BL/6N lines. Lines on this genetic background are used in collaborative research infrastructures for systematic phenotyping, e.g. the International Mouse Phenotyping Consortium (IMPC) and therefore largely cryopreserved in repositories like EMMA/Infrafrontier. The importance of this finding will be especially useful for small laboratories with no or limited access to liquid nitrogen and for laboratories generating many mouse mutant lines by CRISPR/Cas9 who do not want to saturate the limited space of a LN₂ tank, using a more accessible -80 °C freezer. This study underlines, once more, that mouse spermatozoa are very resistant and can be frozen, transported, shared and stored at -80 °C for a long time without a significant loss of viability. This new approach simplifies the freezing process and facilitates the long term storage of mouse spermatozoa at -80 °C, always allowing the transfer to LN₂ for indefinite storage without noticeable detrimental effects.

In Vitro Fertilization in Mice

The success of in vitro fertilization is strongly influenced by genetic background, handling of sperm and oocytes, and culture conditions. This protocol promotes enhanced rates of fertilization by using preincubation medium for sperm containing methyl-β-cyclodextrin (MBCD) and fertilization medium with high calcium and reduced glutathione (GSH).

Mouse Sperm Cryopreservation Using Cryoprotectant Containing l-Glutamine

Efforts to advance sperm cryopreservation are ongoing and include modifications in the cryoprotective agents. The addition of l-glutamine maintains post-thaw motility and reduces plasma membrane damage to sperm.

History of cryobiology, with special emphasis in evolution of mouse sperm cryopreservation

Confucius said study the past if you would define the future and a popular statement says that history depends on who writes it. To talk about history it is necessary to find and define a milestone where to start the narration. The intention of this quick review is to take the reader through moments and selected publications; part and pieces of memories showing how the concept of cryopreservation, specifically for mouse sperm, was conceived and sustained as we know it today. Beginning with the development of the microscope (1677) and continuing through the 17th century with the first documented observation by L. Spallanzani describing that sperm could maintain the motility under cold conditions. As J. Sherman suggested, we divide the cryopreservation evolution into two sequences, previous to and after 1949 when Polge, Smith and Parkes discovered the property of glycerol as cryoprotectant. Later, in 1972, D. Whittingham, S. Leibo, and P. Mazur applying a slow freezing process achieved the first embryo freezing (mouse). During that time many theories were scientifically confirmed. Among those, Peter Mazur demonstrated the relation between the speed of freezing and intracellular ice formation, and Stanley Leibo that each cell type has their unique freezing curve. In 1950, after the discovery of the protective aspect of glycerol, sperm from many mammals were frozen, except from the mouse. It was in the early 90's when the mouse sperm freezing becomes important and it was a real challenge for many groups, nevertheless, the technique using skim milk and raffinose modified by Dr Nakagata was the beginning of a different story ….

Supramolecular Pharmaceutical Sciences: A Novel Concept Combining Pharmaceutical Sciences and Supramolecular Chemistry with a Focus on Cyclodextrin-Based Supermolecules

Supramolecular chemistry is an extremely useful and important domain for understanding pharmaceutical sciences because various physiological reactions and drug activities are based on supramolecular chemistry. However, it is not a major domain in the pharmaceutical field. In this review, we propose a new concept in pharmaceutical sciences termed "supramolecular pharmaceutical sciences," which combines pharmaceutical sciences and supramolecular chemistry. This concept could be useful for developing new ideas, methods, hypotheses, strategies, materials, and mechanisms in pharmaceutical sciences. Herein, we focus on cyclodextrin (CyD)-based supermolecules, because CyDs have been used not only as pharmaceutical excipients or active pharmaceutical ingredients but also as components of supermolecules.

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

Macromolecular crowded conditions strengthen contacts between mouse oocytes and companion granulosa cells during in vitro growth

Macromolecular crowded culture medium formed by addition of polyvinylpyrrolidone (PVP; molecular weight = 360 000), positively influences the viability, growth, and development of bovine oocytes. Owing to its apparently various effects, uncovering the specific mechanisms of crowding responsible for these outcomes is important. The present study was conducted to determine the effects of crowding on oocytes with a particular focus on the intimacy of contacts between oocyte and cumulus/granulosa cells. Growing mouse oocyte-granulosa cell complexes were cultured for 10 days in a modified α-minimum essential medium, supplemented with PVP at a concentration of 0%, 1%, 2%, or 3% (w/v). Although the complexes developed in all groups, 2% and 3% PVP medium induced a substantial morphological modification, and a larger proportion of oocytes associated with cumulus cells survived in 3% PVP medium than in the 0% or 1% PVP medium. No significant difference was found in the frequencies of polar body extrusion (78–88%) and blastocyst formation (approximately 40%) after in vitro fertilization among the experimental groups. Confocal laser scanning microscopy indicated a higher number of transzonal processes reaching the oocyte from cumulus cells in 2% PVP medium than in 0% PVP medium. Transmission electron microscopy depicted close adhesion of the oocyte with cumulus cells in 2% PVP medium —bearing a resemblance to their in vivo counterparts— and loose adhesion in 0% PVP medium. In conclusion, we found that a mechanism for the action of crowded conditions involves the strengthening of contacts and communication between oocytes and companion cumulus/granulosa cells.

Identification of quantitative trait loci associated with the susceptibility of mouse spermatozoa to cryopreservation

Although it is known that the susceptibility of mouse spermatozoa to freezing-thawing varies greatly with genetic background, the underlying mechanisms remain to be elucidated. In this study, to map genetic regions responsible for the susceptibility of spermatozoa to freezing-thawing, we performed in vitro fertilization using spermatozoa from recombinant inbred mice derived from the C57BL/6J and DBA/2J strains, whose spermatozoa showed distinct fertilization abilities after freezing. Genome-wide interval mapping identified two suggestive quantitative trait loci (QTL) associated with fertilization on chromosomes 1 and 11. The strongest QTL on chromosome 11 included 70 genes at 59.237260-61.324742 Mb and another QTL on chromosome 1 included 43 genes at 153.969506-158.217850 Mb. These regions included at least 15 genes involved with testicular expression and possibly with capacitation or sperm motility. Specifically, the Abl2 gene on chromosome 1, which may affect subcellular actin distribution, had polymorphisms between C57BL/6J and DBA/2J that caused at least three amino acid substitutions. A correlation analysis using recombinant inbred strains revealed that the fertilization rate was strongly correlated with the capacitation rate of frozen-thawed spermatozoa after preincubation. This result is consistent with the fact that C57BL/6J frozen-thawed spermatozoa recover their fertilization capacity following treatment with methyl-β-cyclodextrin to enhance sperm capacitation. Thus, our data provide important clues to the molecular mechanisms underlying cryodamage to mouse spermatozoa.

In Vitro Fertilization in Mice

In vitro fertilization (IVF) involves fertilization of mature oocytes with capacitated sperm in a tissue culture dish. This technique can generate large numbers of cleavage-stage embryos without using a significant number of single-caged stud males for mating. In addition, sperm penetration is synchronous during incubation with mature oocytes, leading to synchronous development, unlike fertilization in vivo, when natural ovulation is usually spread over time. These embryos can be used for a variety of applications including rapid strain expansion and generation of age-matched experimental cohorts as well as cryopreservation at the two-cell stage (speed cryo). Another use of IVF is to generate offspring from cryopreserved sperm and from mice that, for one reason or another, will not mate or carry litters to term, that is, strain rescue. The method described here was refined at The Jackson Laboratory and has been in use for several years. There are many published alternative approaches and/or modifications, but this method, which can be used for both fresh and cryorecovered sperm, is relatively simple and effective for a wide variety of strains, although embryo yield varies considerably among strains as a function of response to superovulation and fertilization rate. Optimal results are dependent on practice and attention to detail.

Efficient and scheduled production of pseudopregnant female mice for embryo transfer by estrous cycle synchronization

In embryo transfer experiments in mice, pseudopregnant females as recipients are prepared by sterile mating with vasectomized males. Because only females at the proestrus stage accept males, such females are selected from a stock of animals based on the appearance of their external genital tract. Therefore, the efficiency of preparing pseudopregnant females largely depends on the size of female colonies and the skill of the operators who select females for sterile mating. In this study, we examined whether the efficiency of preparing pseudopregnant females could be improved by applying an estrous cycle synchronization method by progesterone (P4) pretreatment, which significantly enhances the superovulation outcome in mice. We confirmed that after two daily injections of P4 (designated Days 1 and 2) in randomly selected females, the estrous cycles of most females (about 85%) were synchronized at metestrus on Day 3. When P4-treated females were paired with vasectomized males for 4 days (Days 4–8), a vaginal plug was found in 63% (20/32) of the females on Day 7. After the transfer of vitrified-warmed embryos into their oviducts, 52% (73/140) of the embryos successfully developed into offspring, the rate being comparable to that of the conventional embryo transfer procedure. Similarly, 77% (24/31) of females became pregnant by fertile mating with intact males for 3 days, which allowed the scheduled preparation of foster mothers. Thus, our estrous cycle synchronization method may omit the conventional experience-based process of visually observing the vagina to choose females for embryo transfer. Furthermore, it is expected that the size of female stocks for recipients can be reduced to less than 20%, which could be a great advantage for facilities/laboratories undertaking mouse-assisted reproductive technology.

Sperm capacitation pretreatment positively impacts bovine intracytoplasmic sperm injection

The efficiency of intracytoplasmic sperm injection (ICSI) in bovines is low compared to other species due in part to inadequate egg activation and sperm nucleus decondensation after injection. We hypothesized that this low efficiency is due to the lack of complete sperm capacitation, so we evaluated the effects of isobutylmethylxanthine (IBMX) and methyl-β-cyclodextrin (MβCD) on bovine sperm capacitation and on the preimplantation developmental potential of bovine embryos generated by ICSI. Treatment with IBMX and MβCD decreased sperm viability (between 13-30%); nevertheless, 0.4 mM IBMX and 1 mM MβCD increased (p < 0.05) capacitation metrics-that is, acrosome exocytosis, intracellular calcium level, plasma membrane fluidity, and tyrosine phosphorylation-compared to the control. After ICSI, embryos injected with IBMX- and MβCD-treated sperm showed similar cleavage to the untreated group (range 82-88%). Pronucleus formation rate was higher with MβCD-pretreatment (54%) compared to the control group (25%), and blastocyst rate was significantly improved with MβCD-pretreatment (24%) compared to the IBMX (18%) and control (17%) groups. Importantly, embryo quality-as assessed by the total number of cells, cell allocation, and apoptotic cell index-was not affected by the sperm treatments. In conclusion, MβCD pretreatment of sperm improved the efficiency of blastocyst production in bovine ICSI.

Lipid raft dynamics linked to sperm competency for fertilization in mice

It is well known that mammalian sperm acquires fertilization ability after several maturation processes, particularly within the female reproductive tract. In a previous study, we found that both glycosylphosphatidylinositol (GPI)-anchored protein (GPI-AP) release and lipid raft movement occur during the sperm maturation process. In several genetic studies, release of GPI-AP is a crucial step for sperm fertilization ability in the mouse. Here, we show that lipid raft movement is also fundamental for sperm to be competent for fertilization by comparing the sperm maturation process of two mouse inbred strains, C57BL/6 and BALB/c. We found that ganglioside GM1 movement was exclusively reduced in BALB/c compared with C57BL/6 among other examined sperm maturation parameters, such as GPI-AP release, sperm migration to the oviduct, cholesterol efflux, protein tyrosine phosphorylation and acrosome reaction, and was strongly linked to sperm fertility phenotype. The relationship between GM1 movement and in vitro fertilization ability was confirmed in other mouse strains, suggesting that lipid raft movement is one of the important steps for completing the sperm maturation process.

Potential Use of Cyclodextrins as Drug Carriers and Active Pharmaceutical Ingredients

Cyclodextrins (CyDs) are extensively used in various fields, and especially have been widely utilized as pharmaceutical excipients and drug carriers in the pharmaceutical field. Owing to the multi-functional and biocompatible characteristics, CyDs can improve the undesirable properties of drug molecules. This review outlines the current application of CyDs in pharmaceutical formulations, focusing on their use as CyD-based drug carriers for several kinds of drugs. Additionally, CyDs have great potential as active pharmaceutical ingredients against various diseases with few side effects.

Severe damage to the placental fetal capillary network causes mid- to late fetal lethality and reduction in placental size in Peg11/Rtl1 KO mice

Paternally expressed 11/Retrotransposon-like 1 (Peg11/Rtl1) knockout (KO) mice show mid- to late fetal lethality or late fetal growth retardation associated with frequent neonatal lethality. The lethal phenotype is largely dependent on genetic background and becomes more severe with each succeeding generation in the course of backcross experiments to C57BL/6 (B6). We previously suggested that these lethal and growth phenotypes in the fetal stages were due to severe defects in placental fetal capillaries in the labyrinth layer. In this study, we re-examined KO fetuses and placentas and confirmed that the severe clogging of fetal capillaries was associated with KO fetuses showing mid-fetal lethality with internal bleeding. Importantly, the basal region of the fetal capillary network was specifically damaged, also leading to poor expansion of the labyrinth layer and placental size reduction in the later stage. An apparent down-regulation of transmembrane protein 100 (Tmem100), mesenchyme homeobox 2 (Meox2) and lymphatic vessel endothelial hyaluronan receptor 1 (Lyve1) expression were observed in earlier stage placentas even before apparent size reduction became, suggesting that these genes are involved in the maintenance of fetal capillaries associated with Peg11/Rtl1 during development.

Successful in vitro fertilization and generation of transgenics in Black and Tan Brachyury (BTBR) mice

The Black and Tan Brachyury (BTBR) mouse strain is a valuable model for the study of long-term complications from obesity-induced type 2 diabetes mellitus and autism spectrum disorder. Due to technical difficulties with assisted reproduction, genetically modified animals on this background have previously been generated through extensive backcrossing, which is expensive and time-consuming. We successfully generated two separate transgenic mouse lines after direct zygote microinjection into this background strain. Additionally, we developed in vitro fertilization (IVF) methods for the BTBR mouse. We found low rates of fertilization and implantation in this strain, and identified the BTBR oocyte as the primary culprit of low success with BTBR IVF. We achieved an increase in live born pups from 5.9 to 35.6 % with IVF in the BTBR strain by use of BTBR females at a younger age (18-25 days), collection of oocytes 15-17 h after superovulation, and the use of supplemented fertilization media. This method eliminates the need for time consuming assisted embryo manipulations that are otherwise required for success with BTBR oocytes. This advancement provides an exciting opportunity to directly generate BTBR transgenics and gene-edited mice using both traditional and emerging genomic editing techniques, such as CRISPR/Cas9. These methods also allow effective colony preservation and rederivation with these strains. To our knowledge, this is the first report describing embryo manipulations in BTBR mice.

Immunotherapy using inhibin antiserum enhanced the efficacy of equine chorionic gonadotropin on superovulation in major inbred and outbred mice strains

Improvement of the superovulation technique will help to enhance the efficiency of embryo and animal production. Blocking inhibin using inhibin antiserum (IAS) is known to promote follicular development by increasing the level of FSH. Previously, we reported that coadministration of IAS and eCG produced more than 100 oocytes from a single female C57BL/6 mouse at 4 weeks old. The oocytes derived from the IAS + eCG (IASe) treatment were able to fertilize and develop normally into offspring. In this study, we examined the effect of IASe treatment on the numbers of ovulated oocytes in major inbred (A/J, BALB/cByJ, C3HeJ, DBA/2J, and FVB/NJ) and outbred (CD1) mice strains at 4 weeks old. We confirmed the fertilization and developmental ability of the IASe-derived oocytes. IASe treatment ovulated 1.5 to 3.2 times higher numbers of oocytes than eCG treatment alone. The fertilization rate of IASe-derived oocytes was similar to that of eCG-derived oocytes. In vitro and in vivo developmental rates of the embryos derived from IASe were similar to the rates of embryos derived from eCG. We have shown that superovulation by IASe is very effective in obtaining high numbers of ovulated oocytes from small numbers of oocyte donor in a number of mice strains. The superovulation technique will contribute to the archiving of cryopreserved embryos of genetically engineered mice using small numbers of donors and has the potential to produce more live animals for rederivation of the archived mouse lines in mouse repositories.

Mechanisms of fertilization elucidated by gene-manipulated animals

Capacitation and the acrosome reaction are key phenomena in mammalian fertilization. These phenomena were found more than 60 years ago. However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved. Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications. Today, although in vitro fertilization systems remain our central research tool, the importance of in vivo observations must be revisited. Here, primarily focusing on our own research, I summarize how in vivo observations using gene-manipulated animals have elucidated new concepts in the mechanisms of fertilization.

Cryorecovery of Mouse Sperm by Different IVF Methods Using MBCD and GSH

Different protocols incorporating methyl-β-cyclodextrin (MBCD) and reduced glutathione (GSH) have been reported to improve IVF recovery of cryopreserved mouse sperm on a C57BL/6 (J and N) genetic background. However, it is not clear which IVF protocol is most appropriate when using the various methods to cryorecover sperm with different sperm quality and sample volumes. Therefore, in the present study we correlated sperm motility with fertilization rate and compared the efficiency of different IVF methods using various sperm samples so as to establish general guidelines for mouse sperm cryorecovery by IVF. High linear correlation between sperm fertilization rate and progressive motility was found, R² was 0.9623 and 0.9993 for pre-freezing and post-thaw progressive motility, respectively. High amounts of cryoprotective agent (CPA) were observed to impair both sperm capacitation and fertilization. Moreover, the presence of a large number of immotile sperm in the sperm-oocyte co-incubation drop was found to reduce IVF success which could be partially reversed by supplementation using monothioglycerol (MTG) during centrifugation. It was concluded that the efficiency of IVF using cryorecovered mouse sperm in media containing MBCD and GSH can be predicted from sperm progressive motility. High concentrations of CPA and immotile sperm should be mitigated prior to IVF. The optimum IVF method should be selected based on sperm sample volume and sperm parameters.

DNA Scaffolded Silver Clusters: A Critical Study

Fluorescent silver nanoclusters (Ag-NCs) are in prominence as novel sensing materials due to their biocompatibility, photostability, and molecule-like optical properties. The present work is carried out on an array (17 sequences) of 16 bases long cytosine rich, single stranded DNA templates 5′-C₃X_iC₃X_iiC₃X_iiiC₃X_iv-3′ where i, ii, iii, iv correspond to T/G/C deoxynucleobases (with default base A). Among all the oligonucleotides, a sequence C₃AC₃AC₃TC₃G (3T4G) has been identified, which grows three different near-infrared-emitting NC species with absorption/emission maxima at ~620/700 (species I), 730/800 (species II), and 830 (Species III) nm, respectively. The nature of the spectral profiles, along with relevant parameters namely absorption maximum (λabsmax), emission maximum (λemmax), anisotropy (r), lifetime (τ), circular dichroism spectral data are used to understand the microenvironments of the fluorescent NC species I, II, and III. DNA:Ag stiochiometric, pH and solvent dependent studies proved that i-motif scaffolds with different folding topologies are associated with the growth of these three species and a certain concentration of silver and H⁺ favor the growth of species III. Size exclusion chromatographic measurements provided similar indications that a folded, more compact, classic i-motif template is associated with the formation of the longer NIR (~830 nm) absorbing species. This study provides a more definitive approach to design and obtain a targeted DNA templated Ag-NC with required emission properties for biophysical and cellular applications.

Two activators of in vitro fertilization in mice from licorice

Systems for artificial insemination have been established in some animals. However, due to limited availability of sperm and oocytes, more effective treatment methodologies are required. Recently, it was demonstrated that the rate of in vitro fertilization (IVF) in mice was improved by adding a water extract of licorice (Glycyrrhiza uralensis), but not glycyrrhizic acid, to the artificial insemination culture medium. In this study, we examined licorice extract for active compounds using bioassay-guided separation. The results indicated that isoliquiritigenin and formononetin were the active molecules in licorice that contributed to the improved rate of IVF.

Superovulation using the combined administration of inhibin antiserum and equine chorionic gonadotropin increases the number of ovulated oocytes in C57BL/6 female mice

Superovulation is a reproductive technique generally used to produce genetically engineered mice. Superovulation in mice involves the administration of equine chorionic gonadotropin (eCG) to promote follicle growth and then that of human chorionic gonadotropin (hCG) to induce ovulation. Previously, some published studies reported that inhibin antiserum (IAS) increased the number of ovulated oocytes in ddY and wild-derived strains of mice. However, the effect of IAS on the C57BL/6 strain, which is the most widely used inbred strain for the production of genetically engineered mice, has not been investigated. In addition, the combined effect of IAS and eCG (IASe) on the number of ovulated oocytes in superovulation treatment has not been examined. In this study, we examined the effect of IAS and eCG on the number of ovulated oocytes in immature female mice of the C57BL/6 strain in superovulation treatment. Furthermore, we evaluated the quality of obtained oocytes produced by superovulation using IASe by in vitro fertilization (IVF) with sperm from C57BL/6 or genetically engineered mice. The developmental ability of fresh or cryopreserved embryos was examined by embryo transfer. The administration of IAS or eCG had a similar effect on the number of ovulated oocytes in C57BL/6 female mice. The number of ovulated oocytes increased to about 3-fold by the administration of IASe than by the administration of IAS or eCG alone. Oocytes derived from superovulation using IASe normally developed into 2-cell embryos by IVF using sperm from C57BL/6 mice. Fresh or cryopreserved 2-cell embryos produced by IVF between oocytes of C57BL/6 mice and sperm from genetically engineered mice normally developed into live pups following embryo transfer. In summary, a novel technique of superovulation using IASe is extremely useful for producing a great number of oocytes and offspring from genetically engineered mice.

Cysteine analogs with a free thiol group promote fertilization by reducing disulfide bonds in the zona pellucida of mice

Archives of cryopreserved sperm harvested from genetically engineered mice, in mouse resource centers, are a readily accessible genetic resource for the scientific community. We previously reported that exposure of oocytes to reduced glutathione (GSH) greatly improves the fertilization rate of frozen-thawed mouse sperm. Application of GSH to in vitro fertilization techniques is widely accepted as a standard protocol to produce sufficient numbers of mice from cryopreserved sperm. However, the detailed mechanism of the enhancement of fertilization mediated by GSH in vitro is not fully understood. Here we focused on the chemical by determining the effects of its amino acid constituents and cysteine analogs on the fertilization of oocytes by frozen-thawed sperm. Furthermore, we determined the stability of these compounds in aqueous solution. We show here that l-cysteine (l-Cys), d-cysteine (d-Cys), or N-acetyl-l-cysteine (NAC) increased the rate of fertilization when added to the medium but did not adversely affect embryo development in vitro or in vivo. The levels of thiol groups of proteins in the zona pellucida (ZP) and the expansion of the ZP were increased by l-Cys, d-Cys, and NAC. These effects were abrogated by the methylation of the thiol group of l-Cys. NAC was the most stable of these compounds in the fertilization medium at 4°C. These results suggest that the thiol groups of cysteine analogs markedly enhance the fertilization rate of mouse oocytes.

Distinct pathways of cholesterol biosynthesis impact on insulin secretion

Results from previous investigations have indicated that glucose-stimulated insulin secretion (GSIS) is affected by changes in cholesterol and its intermediates, but the precise link between secretion and cholesterol has not been thoroughly investigated. In this study, we show the contribution of both protein isoprenylation and cholesterol-dependent plasma membrane structural integrity to insulin secretion in INS-1E cells and mouse islets. Acute (2 h) inhibition of hydroxyl-methylglutaryl-CoA reductase by simvastatin (SIM) resulted in inhibition of GSIS without reduction in total cellular cholesterol content. This effect was prevented by cell loading with the isoprenyl molecule geranylgeranyl pyrophosphate. Chronic (24 h) inhibition of cholesterol biosynthesis resulted in inhibition of GSIS with a significant reduction in total cellular cholesterol content, which was also observed after the inhibition of cholesterol biosynthesis downstream of isoprenoid formation. Electron paramagnetic resonance analyses of INS-1E cells showed that the SIM-induced reduction in cholesterol increased plasma membrane fluidity. Thus, the blockade of cholesterol biosynthesis resulted in the reduction of availability of isoprenoids, followed by a reduction in the total cholesterol content associated with an increase in plasma membrane fluidity. Herein, we show the different contributions of cholesterol biosynthesis to GSIS, and propose that isoprenoid molecules and cholesterol-dependent signaling are dual regulators of proper β-cell function.

Spermatozoa from mice deficient in Niemann-Pick disease type C2 (NPC2) protein have defective cholesterol content and reduced in vitro fertilising ability

The cholesterol content of the sperm membrane is regulated during both maturation in the epididymis and capacitation in the female tract, two processes required for the spermatozoa to acquire their fertilising ability. Because Niemann-Pick disease, type C2 (NPC2) protein is one of the most abundant components of the epididymal fluid and contains a functional cholesterol-binding site that can transfer cholesterol between membranes, it has been suggested for years that NPC2 could be involved in the regulation of cholesterol levels in spermatozoa during epididymal maturation. In the present study, western blot and immunohistochemistry analyses demonstrated significant levels of NPC2 in the mouse epididymal epithelium. Epididymal spermatozoa obtained from NPC2(-/-) mice were morphologically normal and had normal motility parameters, but had a reduced cholesterol content compared with that of wild-type (WT) spermatozoa, as determined by both biochemical and by flow cytometry analyses. These results suggest that NPC2 could be involved in regulating cholesterol levels in spermatozoa during epididymal maturation. To understand the relevance of epididymal NPC2 for sperm function, the ability of spermatozoa to undergo events influenced by epididymal maturation, such as capacitation and fertilisation, were compared between WT and NPC2(-/-) mice. Capacitated NPC2(-/-) spermatozoa exhibited defective tyrosine phosphorylation patterns and a reduced ability to fertilise cumulus-oocyte complexes compared with WT spermatozoa, supporting the relevance of mouse epididymal NPC2 for male fertility.

Devising assisted reproductive technologies for wild-derived strains of mice: 37 strains from five subspecies of Mus musculus

Wild-derived mice have long offered invaluable experimental models for mouse genetics because of their high evolutionary divergence from laboratory mice. A number of wild-derived strains are available from the RIKEN BioResource Center (BRC), but they have been maintained as living stocks because of the unavailability of assisted reproductive technology (ART). In this study, we sought to devise ART for 37 wild-derived strains from five subspecies of Mus musculus maintained at the BRC. Superovulation of females was effective (more than 15 oocytes per female) for 34 out of 37 strains by treatment with either equine chorionic gonadotropin or anti-inhibin serum, depending on their genetic background (subspecies). The collected oocytes could be fertilized in vitro at mean rates of 79.0% and 54.6% by the optimized protocol using fresh or frozen-thawed spermatozoa, respectively. They were cryopreserved at the 2-cell stage by vitrification with an ethylene glycol-based solution. In total, 94.6% of cryopreserved embryos survived the vitrification procedure and restored their normal morphology after warming. A conventional embryo transfer protocol could be applied to 25 out of the 35 strains tested. In the remaining 10 strains, live offspring could be obtained by a modified embryo transfer protocol using cyclosporin A treatment and co-transfer of ICR (laboratory mouse strain) embryos. Thus, ART for 37 wild-derived strains was devised successfully and is now routinely used for their preservation and transportation. The information provided here might facilitate broader use and wider distribution of wild-derived mice for biomedical research.

Prolonged exposure to hyaluronidase decreases the fertilization and development rates of fresh and cryopreserved mouse oocytes

Hyaluronidase is generally used to remove cumulus cells from mouse oocytes before oocyte cryopreservation, intracytoplasmic sperm injection or DNA injection. In general, use of cumulus-free mouse oocytes decreases in vitro fertilizing ability compared with cumulus-surrounded oocytes. The effect of hyaluronidase exposure on the quality of mouse oocytes is not fully understood. Here, we investigated the effect of hyaluronidase exposure time on the fertilization rate of fresh and vitrified mouse oocytes and their subsequent developmental ability in vitro. We found that the fertilization rate decreased with hyaluronidase treatments. This reduction in the fertilization rate following treatment with hyaluronidase was fully reversed by removal of the zona pellucida. In addition, oocytes treated with hyaluronidase for 5 min or longer had a reduced capacity to develop to the morula and blastocyst stage. The survival, fertilization, and developmental rates of vitrified-warmed oocytes were also reduced by longer exposure to hyaluronidase. In conclusion, these results suggest that prolonged exposure to hyaluronidase decreases the quality of mouse oocytes and shorter hyaluronidase treatment times may help achieve a stable and high fertilization rate in fresh and cryopreserved oocytes.

Contemporary techniques for freezing mouse spermatozoa

Each year, thousands of new mouse models are generated around the world to further biomedical research. Unfortunately, the cost of maintaining mouse colonies makes it uneconomical to keep strains on the shelf that are not part of active research programs. Ideally, these retired strains should be archived. If this is not done and the line is simply killed off, the genetics are lost to future generations of scientists. Traditionally, embryo freezing has been used to cryopreserve mice, but this is expensive, time consuming, requires large numbers of donor females, and usually involves invasive superovulation procedures. Sperm freezing circumvents all of these disadvantages and is rapidly becoming the technique of choice for many repositories. This has been made possible through the use of refined cryoprotective agents and the development of improved in vitro fertilization techniques. This article describes two popular sperm freezing techniques employed by mouse repositories to archive spermatozoa using cryoprotective agents supplemented with either L-glutamine or monothioglycerol.

Microdroplet in vitro fertilization can reduce the number of spermatozoa necessary for fertilizing oocytes

Successful in vitro fertilization (IVF) in mice has been achieved using spermatozoa at concentrations specifically optimized for the experimental conditions, such as species and source of spermatozoa. Although IVF in mice is mostly performed using about 80–500 µl drops, it is expected that the number of spermatozoa used for insemination can be reduced by decreasing the size of the IVF drops. The present study was undertaken to examine the extent to which the number of spermatozoa used for IVF could be reduced by using small droplets (1 µl). We devised the experimental parameters using frozen–thawed spermatozoa from C57BL/6 mice in anticipation of broader applications to other mouse facilities. We found that as few as 5 spermatozoa per droplet could fertilize oocytes (1 or 3 oocytes per droplet), although the fertilization rates were low (13–15%). Practical fertilization rates (> 40%) could be achieved with frozen-thawed C57BL/6J spermatozoa, which are sensitive to cryopreservation, when 20 sperm per droplet were used to inseminate 3 oocytes. Even with spermatozoa from a very poor quality suspension (10% motility), about 25% of oocytes were fertilized. Our calculations indicate that the number of inseminated spermatozoa per oocyte can be reduced to 1/96–1/240 by this method. In two separate embryo transfer experiments, 60% and 47%, respectively, of embryos developed to term. Our microdroplet IVF method may be particularly advantageous when only a limited number of motile spermatozoa are available because of inadequate freezing-thawing or genetic reasons.

Rescue in vitro fertilization method for legacy stock of frozen mouse sperm

Sperm cryopreservation has been widely adopted for maintenance of the genetically engineered mouse (GEM). The cryopreserved sperm are being exchanged among many institutes worldwide. However, the recipients are not always able to obtain high fertilization rates with the frozen sperm shipped from senders. In this study, we cryopreserved mouse sperm via various methods and performed in vitro fertilization (IVF) in which the combination of methyl-beta-cyclodextrin for sperm preincubation and reduced glutathione for insemination was used (the MBCD-GSH IVF). In addition, frozen sperm sent from the Jackson Laboratory (USA) were thawed and used for IVF in the same manner. The fertilization rates of both the sperm cryopreserved via the methods applied in some countries and the cryopreserved GEM sperm improved when used with the MBCD-GSH IVF method. Therefore, we strongly believe that the MBCD-GSH IVF method brings about relatively high fertilization rates with any strain of frozen mouse sperm.

Rapid conversion of EUCOMM/KOMP-CSD alleles in mouse embryos using a cell-permeable Cre recombinase

We describe here use of a cell-permeable Cre to efficiently convert the EUCOMM/KOMP-CSD tm1a allele to the tm1b form in preimplantation mouse embryos in a high-throughput manner, consistent with the requirements of the International Mouse Phenotyping Consortium-affiliated NIH KOMP2 project. This method results in rapid allele conversion and minimizes the use of experimental animals when compared to conventional Cre transgenic mouse breeding, resulting in a significant reduction in costs and time with increased welfare benefits.