Fundamental cryobiology of reproductive cells and tissues

Cryopreservation and revival of mesenchymal stromal cells

Over the past few years, the pace of preclinical stem cell research is astonishing and adult stem cells have become the subject of intense research. Due to the presence of promising supporting preclinical data, human clinical trials for stem cell regenerative treatment of various diseases have been initiated. As there has been a precedent for the use of bone marrow stem cells in the treatment of hematological malignancies and ischemic heart diseases through randomized clinical safety and efficacy trials, the development of new therapies based on culture-expanded human mesenchymal stromal cells (MSCs) opens up new possibilities for cell therapy. To facilitate these applications, cryopreservation and long-term storage of MSCs becomes an absolute necessity. As a result, optimization of this cryopreservation protocol is absolutely critical. The major challenge during cellular cryopreservation is the lethality associated with the cooling and thawing processes. The major objective is to minimize damage to cells during low temperature freezing and storage and the use of a suitable cryoprotectant. The detrimental effects of cellular cryopreservation can be minimized by controlling the cooling rate, using better cryoprotective agents, maintaining appropriate storage temperatures, and controlling the cell thawing rate. As is described in this chapter, human MSCs can either be frozen in cryovials or in freezing bags together with cryopreserve solutions containing dimethyl sulfoxide (DMSO).

Frozen-thawed rhesus sperm retain normal morphology and highly progressive motility but exhibit sharply reduced efficiency in penetrating cervical mucus and hyaluronic acid gel

The preservation of the genetic diversity of captive populations of rhesus monkeys is critical to the future of biomedical research. Cryopreservation of rhesus macaque sperm is relatively simple to perform, yields high post-thaw motility, and theoretically, provides via artificial insemination (AI) a way to easily transfer genetics among colonies of animals. In the interest of optimizing semen cryopreservation methods for use with vaginal AI, we evaluated the ability of frozen-thawed rhesus sperm to penetrate periovulatory cervical mucus (CM). Motile sperm concentration of pre-freeze ("fresh") and post-thawed ("thawed") samples from five different males were normalized for both computer assisted sperm motion analysis and CM penetration experiments. Sperm samples were deposited into slide chambers containing CM or gel composed of hyaluronic acid (HA) as a surrogate for CM and numbers of sperm were recorded as they entered a video field a preset distance from the sperm suspension-CM (or HA) interface. Fresh and thawed sperm were dried on glass slides, "Pap"-stained, and assessed for changes in head dimensions and head and flagellar shape. While retaining better than 80% of fresh sperm progressive motility, thawed sperm from the same ejaculate retained on average only 18.6% of the CM penetration ability. Experiments using HA gel yielded similar results only with reduced experimental error and thus improved detection of treatment differences. Neither the percentage of abnormal forms nor head dimensions differed between fresh and thawed sperm. While findings suggests that sperm-CM interaction is a prominent factor in previous failures of vaginal AI with cryopreserved macaque sperm, neither sperm motility nor morphology appears to account for changes in the ability of cryopreserved sperm to penetrate CM. Our data points to a previously unidentified manifestation of cryodamage which may have implications for assessment of sperm function beyond the cervix and across mammalian species.

Effect of cryopreservation on fish sperm subpopulations

The evaluation of the motility data obtained with a CASA system, applying a Two-Step Cluster analysis, identified in seabream sperm 3 different sperm subpopulations that correlated differently with embryo hatching rates. Hence, we designed an experiment to understand the effect of the application of different cryopreservation protocols in these sperm motility-based subpopulations. We analyzed Sparus aurata frozen/thawed semen motility 15, 30, 45 and 60s after activation, using CASA software. Different protocols were applied for cryopreservation: three different cryoprotectants (Dimethyl Sulfoxide (Me(2)SO), Ethylene Glycol (EG) and Propylene Glycol (PG)) each at two different concentrations and two packaging volumes (0.5ml straws, and 1.8ml cryovials) were tested. Different freezing rates were evaluated corresponding to 1, 2, 3, 4 and 8cm above the liquid nitrogen surface for the straws and 1, 2 and 4cm for the cryovials. Motility parameters rendered by CASA were treated with a Two-Step Cluster analysis. Three different subpopulations were obtained: SP1 - slow non-linear spermatozoa, SP2 - slow linear spermatozoa and SP3 - fast linear spermatozoa. We considered SP3 as the subpopulation of interest and focused further analyses on it. Generally, SP3 was the best represented subpopulation 15s after activation and was also the one showing a greater decrease in time, being the least represented after 60s. According to the applied univariate general linear model, samples frozen in straws with 5% Me(2)SO and in cryovials with 10% Me(2)SO at 2 and 1cm from the LN(2,) respectively, produced the best results (closer to the control). Clustering analysis allowed the detection of fish sperm subpopulations according to their motility pattern and showed that sperm composition in terms of subpopulations was differentially affected by the cryopreservation protocol depending on the cryoprotectant used, freezing rates and packaging systems.

Cryopreservation of Mammalian oocyte for conservation of animal genetics

The preservation of the female portion of livestock genetics has become an international priority; however, in situ conservation strategies are extremely expensive. Therefore, efforts are increasingly focusing on the development of a reliable cryopreservation method for oocytes, in order to establish ova banks. Slow freezing, a common method for cryopreservation of oocytes, causes osmotic shock (solution effect) and intracellular ice crystallization leading to cell damage. Vitrification is an alternative method for cryopreservation in which cells are exposed to a higher concentration of cryoprotectants and frozen with an ultra rapid freezing velocity, resulting in an ice crystal free, solid glass-like structure. Presently, vitrification is a popular method for cryopreservation of embryos. However, vitrification of oocytes is still challenging due to their complex structure and sensitivity to chilling.

Cryopreservation and oxidative stress in reproductive cells

In spite of the optimisation of cryopreservation protocols, post-thawing trauma to mammalian gametes cannot be completely avoided. Based on recent literature, cellular cryodamage in reproductive cells has been extensively characterised in terms of changes in the cell structure, whereas biochemical alterations have been poorly investigated. The present paper reviews the current knowledge about the involvement of oxidative stress in frozen-thawed cells by considering the most relevant studies in sperm and oocytes. Recognising that spermatozoa are highly susceptible to oxidative damage induced by cryopreservation, the need for further research is highlighted in order to understand whether changes in the redox state have a role in the reduced developmental potential of cryopreserved human reproductive cells.

A new method for cryopreserving adipose-derived stem cells: an attractive and suitable large-scale and long-term cell banking technology

Recent studies have shown potential ways for improving stem cell cryopreservation. The major need for autologous stem cell use is a long-term storage: this arises from the humans' hope of future use of their own cells. Therefore, it is important to evaluate the cell potential of vitality and differentiation before and after cryopreservation. Although several studies have shown a long-term preservation of adipose tissue, a few of them focused their attention to stem cells. The aim of this study was to evaluate the fate of cryopreserved stem cells collected from adipose tissue and stored at low a temperature in liquid nitrogen through an optimal cryopreservation solution (using slowly cooling in 6% threalose, 4% dimethyl sulfoxide, and 10% fetal bovine serum) and to develop a novel approach to efficiently preserve adipose-derived stem cells (ASCs) for future clinical applications. Results showed that stem cells, after being thawed, are still capable of differentiation and express all surface antigens detected before storage, confirming the integrity of their biology. In particular, ASCs differentiated into adipocytes, showed diffuse positivity for PPARgamma and adiponectin, and were also able to differentiate into endothelial cells without addition of angiogenic factors. Therefore, ASCs can be long-term cryopreserved, and this, due to their great numbers, is an attractive tool for clinical applications as well as of impact for the derived market.

Rat strain repositories

More than 500 inbred rat strains have been developed during the past 100 years for a wide range of biomedical applications. In addition to these traditionally bred strains, many induced mutants and several thousand mutagenized sperm samples have recently been generated. At present this huge number of strains is mainly managed by two rat resource centers, the National Bio Resource Project for the Rat in Japan (NBRP-Rat) and the US based Rat Resource and Research Center (RRRC). These resource centers not only collect, maintain and distribute rat strains as animals or cryopreserved embryos and spermatozoa, but also perform additional tasks such as phenotypic and genetic characterization as well as microbiological cleaning. Furthermore, they support researchers through informative databases in the selection of rat strains for specific research purposes. These global rat resource centers are essential for successful and sustainable research using the rat as a model species.

Soy lecithin replaces egg yolk for cryopreservation of human sperm without adversely affecting postthaw motility, morphology, sperm DNA integrity, or sperm binding to hyaluronate

Semen specimens (one ejaculate from each of 20 consenting study participants) were subjected to routine semen analysis, an in vitro sperm binding assay (HBA), and a sperm chromatin dispersion assay (HaloSperm), both before and after cryopreservation using cryoprotectant media supplemented with either egg yolk or soy lecithin. Comparing the equivalency of the two phospholipid cryopreservation supplements with regard to postthaw functional parameters demonstrated that there were no statistically significant differences between the two supplements for [1] recovery of motile sperm, [2] maintenance of sperm cell morphology, [3] maintenance of the ability of sperm to bind to hyaluronate in vitro, or [4] maintenance of sperm DNA integrity.

Collection, cryopreservation, and characterization of human dental pulp-derived mesenchymal stem cells for banking and clinical use

Recent studies have shown that mesenchymal stem cells (MSC) with the potential for cell-mediated therapies and tissue engineering applications can be isolated from extracted dental tissues. Here, we investigated the collection, processing, and cryobiological characteristics of MSC from human teeth processed under current good tissue practices (cGTP). Viable dental pulp-derived MSC (DPSC) cultures were isolated from 31 of 40 teeth examined. Of eight DPSC cultures examined more thoroughly, all expressed appropriate cell surface markers and underwent osteogenic, adipogenic, and chondrogenic differentiation in appropriate differentiation medium, thus meeting criteria to be called MSC. Viable DPSC were obtained up to 120 h postextraction. Efficient recovery of DPSC from cryopreserved intact teeth and second-passage DPSC cultures was achieved. These studies indicate that DPSC isolation is feasible for at least 5 days after tooth extraction, and imply that processing immediately after extraction may not be required for successful banking of DPSC. Further, the recovery of viable DPSC after cryopreservation of intact teeth suggests that minimal processing may be needed for the banking of samples with no immediate plans for expansion and use. These initial studies will facilitate the development of future cGTP protocols for the clinical banking of MSC.

Individual variability in post-thaw sperm survival in a captive koala population

This study documented the extent of individual animal variation with respect to two proven methods of sperm cryopreservation in a captive population of 22 koalas. Semen samples were collected by electroejaculation, diluted in Tris-citrate glucose and equilibrated to 4 degrees C before being further diluted and frozen in media containing a final concentration of either 14% (v/v) glycerol or 12.5% (v/v) dimethylacetamide (DMA). There were significant differences in post-thaw survival of spermatozoa from different animals that were independent of pre-freeze semen quality. Glycerol proved to be a better cryoprotectant than DMA in terms of maintaining motility, plasma membrane integrity and high mitochondrial membrane potential; however, there was no difference between cryoprotectants with regards to their ability to prevent chromatin relaxation. While a positive correlation was observed between motility and mitochondrial membrane potential, both before and after cryopreservation, the slopes of the pre-freeze regression lines of these relationships were significantly altered following cryopreservation, suggesting that the efficiency of energy generation by the mitochondria was lowered by the freeze-thaw process. Based on a cluster analysis of the post-thaw semen viability parameters, the koalas in this study could be divided into two distinct groups; Cluster 1 had significantly higher sperm viability compared to the other cluster, regardless of the cryoprotectant used. The unpredictability of assessing post-thaw survival from pre-freeze koala semen parameters requires further investigation but is likely to be associated with variation in ejaculate composition or inherent genetic differences between animals.

Effects of estrous cycle stage and transport temperature of ovaries on in vitro maturation of canine oocytes

Unlike other domestic animals, in vitro maturation (IVM) of canine oocytes still has limited success. The present study investigated the effects of estrous cycle stage and transport temperature of ovaries on in vitro maturation of canine oocytes. The donor bitches were categorized into three groups based on stage of estrus cycle: follicular (proestrus or estrous), luteal (diestrus) and anestrus. One ovary of each pair collected from 39 mature bitches was transported in Phosphate Buffer Saline (PBS) at 4 degrees C while the other was transported at 37 degrees C. A total of 1138 Grade I COCs obtained from all ovaries were grouped and matured in modified synthetic oviduct fluid (mSOF) supplemented with follicle stimulating hormone (FSH), luteinizing hormone (LH), essential and non-essential amino acids at 38.5 degrees C in a humidified 5% CO(2), 5% O(2), and 90% N(2) atmosphere for 72 h. The nuclear maturation rates were evaluated by aceto-orcein staining. Oocytes harvested from follicular and luteal ovaries have a significantly higher maturation rates (MI+MII) than the oocytes from anestrual ovaries in the 37 degrees C group (p<0.05). However, oocytes harvested from anestrual ovaries transported at 4 degrees C had the highest maturation (MI+MII) rate, and the difference between anestrual and luteal ovary groups was significant (p<0.05). The oocytes from anestrual ovaries transported at 4 degrees C have significantly higher maturation rates than those transported at 37 degrees C (p<0.0001). However, the transport temperature (37 or 4 degrees C) did not significantly affect the maturation (MI+MII) rates of oocytes harvested from the luteal (p=0.61) and follicular (p=0.48) stage ovaries. It can be concluded from this study that (1) both transport temperature and transport temperaturexestrus cycle stage interaction effected the maturation rates, while estrus cycle stage alone did not, and (2) transporting canine ovaries at 4 degrees C can improve in vitro maturation rates in oocytes harvested from anestrous ovaries.

Developmental competence of domestic cat oocytes from ovaries stored at various durations at 4 degrees C temperature

Temporal storage of ovaries can provide opportunity to rescue oocytes from ovaries of endangered felids. The objective of the study was to examine the effect of different storage periods (2, 24 and 48h) of ovaries at 4 degrees C for maturation of cat oocytes in vitro. Ovaries were collected from 25 domestic cats at various stages of the estrous cycle by routine ovariohysterectomy following anesthesia at different local veterinary clinics, and maintained in physiological saline at 4 degrees C for 2, 24 or 48h until oocytes recovery. Selected COCs were maturated at 38 degrees C for 48h in four-well petri dishes, which included 500microL modified synthetic oviduct fluid (mSOF) medium under mineral oil in a humidified 5% CO(2), 5% O(2), and 90% N(2) atmosphere incubator. After the in vitro maturation period, there were no differences between the rate of oocytes matured at MII stages in 2 and 24h storage groups (50.7% and 48.2% respectively, p>0.05). However, the same result for the 48h group was significantly lower than the 2 and 24h groups (28.0%, p<0.001). Our results suggest that while 2 or 24h storage of ovaries at 4 degrees C does not affect the meiotic competence of oocytes in vitro, 48h storage of ovaries decrease the results dramatically.

Effects of methyl-beta-cyclodextrin and cholesterol on cryosurvival of spermatozoa from C57BL/6 mouse

MBCD and Cholesterol-Loaded-Cyclodextrin (CLC) were examined for their abilities to increase the cryosurvival of C57BL/6 mouse sperm, the main strain of genetically engineered mice. The intactness of acrosome and motility of frozen/thawed spermatozoa were used to monitor cryosurvival. In this experimental study, male mice were randomly divided in 6 groups: control 1, experimental 1, experimental 2, control 2, experimental 3 and experimental 4. In experimental groups 1 and 2 spermatozoa were exposed to 0.75 and 1 mM MBCD and in experimental groups 3 and 4 were exposed to two different concentrations of CLC (1 and 2 mg mL(-1)) over a period of 1 h and were subsequently cryopreserved. Spermatozoa in control 1 group were frozen without any exposure to CLC or MBCD and in control 2 (vehicle), sperms were incubated with 4 mM MBCD. The post-thaw sperms were evaluated for their motility and acrosomal status. The values of the intact acrosome and motility increased significantly with concentration of CLC compared to controls and MBCD experimental groups (p<0.05). These results indicate that cryosurvival of C57BL/6 mouse spermatozoa is enhanced by exposure to MBCD which loaded with cholesterol (CLC) before freezing and MBCD alone can not protect sperm from freeze-thaw damage efficiently compare to CLC.

Vitrification: an effective new approach to oocyte banking and preserving fertility in cancer patients

INTRODUCTION

Oocyte cryopreservation is a useful tool for preserving the fertility of cancer patients at risk of losing ovarian function due to undergoing potentially sterilising therapies. Results obtained with different cryopreservation protocols have been disappointing, particularly those obtained with slow cooling procedures. The efficacy of vitrification as an application in clinical practice has recently been demonstrated. The aim of this study is to report results obtained with the Cryotop method of oocyte vitrification in a population of healthy women and to point out its potential usefulness for fertility preservation in oncological patients.

MATERIALS AND METHODS

The study population consisting of non-oncological patients included 47 oocyte donors and 57 recipients undergoing an oocyte donation cycle of assisted reproductive technology (ART). A total of 693 mature metaphase II oocytes were collected following ovarian stimulation using long protocol down-regulation plus gonadotropin administration. Vitrification was carried out by means of the Cryotop method. Oocytes were donated to a compatible recipient after endometrial preparation.

RESULTS

Of the 693 oocytes, 666 (96.1%) survived. A total of 487 (73.1%) were fertilised successfully. One hundred and seventeen embryos were transferred to 57 recipients. Pregnancy rate per transfer and implantation rates were 63.2% and 38.5% respectively. Twenty-eight healthy babies were later born.

CONCLUSIONS

Oocyte cryo-banking by means of the Cryotop vitrification method represents a viable option for healthy women, producing excellent survival rates and a clinical outcome similar to that obtained with fresh oocytes. This approach could potentially be used in cancer patients who want to safeguard their fertility. Cancer patients could potentially benefit from this approach by storing their oocytes before the onset of the oncological therapy.

Reversible disassembly of the actin cytoskeleton improves the survival rate and developmental competence of cryopreserved mouse oocytes

Effective cryopreservation of oocytes is critically needed in many areas of human reproductive medicine and basic science, such as stem cell research. Currently, oocyte cryopreservation has a low success rate. The goal of this study was to understand the mechanisms associated with oocyte cryopreservation through biophysical means using a mouse model. Specifically, we experimentally investigated the biomechanical properties of the ooplasm prior and after cryopreservation as well as the consequences of reversible dismantling of the F-actin network in mouse oocytes prior to freezing. The study was complemented with the evaluation of post-thaw developmental competence of oocytes after in vitro fertilization. Our results show that the freezing-thawing process markedly alters the physiological viscoelastic properties of the actin cytoskeleton. The reversible depolymerization of the F-actin network prior to freezing preserves normal ooplasm viscoelastic properties, results in high post-thaw survival and significantly improves developmental competence. These findings provide new information on the biophysical characteristics of mammalian oocytes, identify a pathophysiological mechanism underlying cryodamage and suggest a novel cryopreservation method.

Challenge from the simple: some caveats in linearization of the Boyle-van't Hoff and Arrhenius plots

Some aspects of proper linearization of the Boyle-van't Hoff (BVH) relationship for calculation of the osmotically inactive volume v(b), and Arrhenius plot (AP) for the activation energy E(a) are discussed. It is shown that the commonly used determination of the slope and the intercept (v(b)), which are presumed to be independent from each other, is invalid if the initial intracellular molality m(0) is known. Instead, the linear regression with only one independent parameter (v(b)) or the Least Square Method (LSM) with v(b) as the only fitting LSM parameter must be applied. The slope can then be calculated from the BVH relationship as the function of v(b). In case of unknown m(0) (for example, if cells are preloaded with trehalose, or electroporation caused ion leakage, etc.), it is considered as the second independent statistical parameter to be found. In this (and only) scenario, all three methods give the same results for v(b) and m(0). AP can be linearized only for water hydraulic conductivity (L(p)) and solute mobility (omega(s)) while water and solute permeabilities P(w) identical withL(p)RT and P(s) identical withomega(s)RT cannot be linearized because they have pre-exponential factor (RT) that depends on the temperature T.

Successful vitrification of human amnion-derived mesenchymal stem cells

BACKGROUND

A cryopreservation protocol for human amnion-derived mesenchymal stem cells (HAMs) is required because these cells cannot survive for long periods in culture. The aim of this study was to determine whether vitrification is a useful freezing method for storage of HAMs.

METHODS

HAMs were cryopreserved using vitrification method. The morphology and viability of thawed HAMs was evaluated by Trypan Blue staining. The expression of several embryonic stem cell (ESC) markers was evaluated using flow cytometry, RT-PCR and immunocytochemistry. Von Kossa, Oil Red O and Alcian Blue staining were used to asses the differentiation potential of thawed HAMs.

RESULTS

The post-thawing viability of HAMs was 84.3 +/- 3.2% (Mean +/- SD, n = 10). The thawed HAMs showed morphological characteristics indistinguishable from the non-vitrified fresh HAMs. The expression of surface antigens (strong positive for CD44, CD49d, CD59, CD90, CD105 and HLA-ABC; weak positive for HLA-G; negative for CD31, CD34, CD45, CD106, CD117 and HLA-DR) and the expression of ESC markers [CK18, fibroblast growth factor-5, GATA-4, neural cell adhesion molecule, Nestin, Oct-4, stem cell factor, HLA-ABC, Vimentin, bone morphogenetic protein (BMP) 4, hepatocyte nuclear factor 4 alpha (HNF-4 alpha), Pax-6, alpha-fetoprotein, Brachyury, BMP-2, TRA-1-60, stage-specific embryonic antigen (SSEA-3, SSEA-4)] were maintained in the vitrified-thawed HAMs. The thawed HAMs retained ability to differentiate into osteoblasts, adipocytes and chondrocytes under appropriate culture conditions.

CONCLUSIONS

Our results suggest that vitrification is a reliable and effective method for cryopreservation of HAMs.

Open-pulled straw (OPS) vitrification of in vitro fertilised mouse embryos at various stages

The present study was designed to investigate the cryotolerance of in vitro fertilised (IVF) mouse embryos at various preimplantation developmental stages. IVF mouse embryos were vitrified by the open-pulled straw (OPS) method. After warming, embryos were morphologically evaluated and assessed by their development to blastocysts, hatched blastocysts or term. The results showed that a high proportion (93.3-100.0%) of vitrified embryos at all developmental stages were morphologically normal after recovery. The developmental rate of vitrified 1-cell embryos to blastocyst (40.0%) or hatched blastocyst (32.7%) or term (9.3%) was significantly lower than that from other stages (P < 0.05). Vitrified embryos from 2-cell to early blastocyst stage showed similar blastocyst (71.8-89.5%) and hatched blastocyst rates (61.1-69.6%) and could develop to term without a significant loss of survival compared with those of fresh embryos (P > 0.05). Vitrified 2-cell embryos showed the highest survival rate in vivo (50.6%, 88/174), compared with that from other stages (9.3-30.5%, P < 0.05). The data demonstrate that the OPS method is suitable for the cryopreservation of IVF mouse embryos from 2-cell stage to early blastocyst stage without a significant loss of survival. Embryos at the 2-cell stage had the best tolerance for cryopreservation in the present study.

Investigations on the heat transport capability of a cryogenic oscillating heat pipe and its application in achieving ultra-fast cooling rates for cell vitrification cryopreservation

Theoretically, direct vitrification of cell suspensions with relatively low concentrations ( approximately 1 M) of permeating cryoprotective agents (CPA) is suitable for cryopreservation of almost all cell types and can be accomplished by ultra-fast cooling rates that are on the order of 10(6-7) K/min. However, the methods and devices currently available for cell cryopreservation cannot achieve such high cooling rates. In this study, we constructed a novel cryogenic oscillating heat pipe (COHP) using liquid nitrogen as its working fluid and investigated its heat transport capability to assess its application for achieving ultra-fast cooling rates for cell cryopreservation. The experimental results showed that the apparent heat transfer coefficient of the COHP can reach 2 x 10(5) W/m(2).K, which is two orders of the magnitude higher than traditional heat pipes. Theoretical analyzes showed that the average local heat transfer coefficient in the thin film evaporation region of the COHP can reach 1.2 x 10(6) W/m(2).K, which is approximately 10(3) times higher than that achievable with standard pool-boiling approaches. Based on these results, a novel device design applying the COHP and microfabrication techniques is proposed and its efficiency for cell vitrification is demonstrated through numerical simulation. The estimated average cooling rates achieved through this approach is 10(6-7)K/min, which is much faster than the currently available methods and sufficient for achieving vitrification with relatively low concentrations of CPA.

An improved cryopreservation method for a mouse embryonic stem cell line

Embryonic stem (ES) cell lines including the C57BL/6 genetic background are central to projects such as the Knock-Out Mouse Project, North American Conditional Mouse Mutagenesis Program, and European Conditional Mouse Mutagenesis Program, which seek to create thousands of mutant mouse strains using ES cells for the production of human disease models in biomedical research. Crucial to the success of these programs is the ability to efficiently cryopreserve these mutant cell lines for storage and transport. Although the ability to successfully cryopreserve mouse ES cells is often assumed to be adequate, the percent post-thaw recovery of viable cells varies greatly among genetic backgrounds and individual cell lines within a genetic background. Therefore, there is a need to improve the efficiency and reduce the variability of current mouse ES cell cryopreservation methods. To address this need, we employed the principles of fundamental cryobiology to improve the cryopreservation protocol of a C57BL/6 mouse ES cell line by characterizing the membrane permeability characteristics and osmotic tolerance limits. These values were used to predict optimal cooling rates, warming rates, and type of cryoprotectant, which were then verified experimentally. The resulting protocol, generated through this hypothesis-driven approach, resulted in a 2-fold increase in percent post-thaw recovery of membrane-intact ES cells as compared to the standard freezing protocol, as measured by propidium iodide exclusion. Additionally, our fundamental cryobiological approach to improving cryopreservation protocols provides a model system by which additional cryopreservation protocols may be improved in future research for both mouse and human ES cell lines.

[Procedures for fertility preservation in female cancer patients]

Improving survival rates and quality of life following modern combined cancer treatments have resulted a growing number of patients requesting maintenance of reproductive functions. Several methods are currently available to maintain fertility during oncotherapy. Even though most of them are still experimental and their efficacy and safety have not been determined, the future for fertility preservation in women with cancer is promising. In vitro fertilization with embryo cryopreservation offers an established method, but time to delay cancer treatment could be risky regarding the progression of several cancer types. Moreover, exposure to a high oestrogen milieu during ovarian stimulation is undesirable when patients have estrogen-sensitive malignant tumours. Cryopreservation of mature oocytes following in vitro fertilization and intracytoplasmatic sperm injection offers advantages, but it is still limited due to its low success rate. Emerging techniques of ovarian tissue cryopreservation followed by autotransplantation have been clinically explored. Novel technologies of tissue freezing and thawing promise improving results. However, only one live birth following autotransplanted frozen-thawed ovarian tissue has been established. This procedure can be offered in the future for prepubertal girls before cancer treatment to maintain future fertility. Gonadal tissue cryopreservation and transplantation should be considered experimental in humans for the present time until greater evidence regarding efficacy and safety is accrued.

Virtues and limitations of the preimplantation mouse embryo as a model system

The mouse is the most widely used model of preimplantation embryo development, but is it a good model? Its small size, prolificacy and ease of handling make the mouse a relatively low cost, readily available and attractive alternative when embryos from other species are difficult or expensive to obtain. However, the real power of the mouse as a model lies in mouse genetics. The development of inbred mouse strains facilitated gene discovery as well as our understanding of gene function and regulation while the development of tools to introduce precise genetic modifications uniquely positioned the mouse as a powerful model system for uncovering gene function. However, all models have limitations; the small size of the mouse limits tissue availability and manipulations that can be performed and differences in physiology among species may make it inappropriate to extrapolate from the mouse to other species. Thus, rather than extrapolating directly from the mouse to other species, it may be more useful to use the mouse as a model system for developing and refining hypotheses to be tested directly in species of interest. In this brief review, the value of the preimplantation mouse embryo as a model is considered, both as a model for other species and as a model for the mouse, as understanding the virtues and limitations of the mouse as a model system is essential to its appropriate use.

Development of a cryopreservation protocol for long-term storage of black tiger shrimp (Penaeus monodon) spermatophores

The objectives of this study were to determine the effect of cryoprotectants on sperm viability and develop a freezing protocol for long-term storage of P. monodon spermatophores. Spermatophores suspended for 30 min in calcium-free saline (Ca-F saline) containing the cryoprotectants dimethyl sulfoxide (DMSO), ethylene glycol (EG), 1,2-propylene glycol (PG), formamide, and methanol at concentrations of 5, 10, 15, or 20% were studied using a modified eosin-nigrosin staining technique. The smallest reductions in apparent sperm viability occurred with DMSO; therefore, a freezing protocol was developed using Ca-F saline containing 5% DMSO. Spermatophores were cryopreserved using three protocols; cooling to a final temperature of -30, -80 or -80 degrees C and immediately stored in liquid nitrogen (cooling rates of -2, -4, -6, -8, -10, -12, -14 or -16 degrees C/min). Frozen spermatophores were thawed (2 min) at 30, 60, 70, or 90 degrees C. Successful cryopreservation of spermatophores in liquid nitrogen was achieved by a one-step cooling rate of -2 degrees C/min between 25 and -80 degrees C before storing in liquid nitrogen. Optimal thawing was in a 30 degrees C water bath for 2 min; this yielded live sperm after storage in liquid nitrogen for 210 days. Average sperm viability for fresh (97.8+/-2.9%) and cryopreserved spermatophores held for less than 60 days (87.3+/-4.1%) did not differ (P>0.05); however, that for spermatophores stored in liquid nitrogen between 90 and 210 days were lower (P<0.05) and varied from 27.3+/-3.4 to 53.3+/-4.3%. Thawed spermatophores previously held in liquid nitrogen for less than 62 days fertilized eggs (fertilization and hatching rates of 71.6-72.2% and 63.6-64.1%, respectively) at rates comparable to fresh spermatophores (70.8-78.2% and 66.3-67.8%, respectively). In conclusion, sperm within cryopreserved spermatophores stored in liquid nitrogen retained their viability for up to 210 days.

A perspective on the role of emerging technologies for the propagation of companion animals, non-domestic and endangered species

Assisted reproductive technologies (ART) have been used successfully in humans, domestic and laboratory species for many years. In contrast, our limited knowledge of basic reproductive physiology has restricted the application of ART in companion animal, non-domestic and endangered species (CANDES). Although there are numerous benefits, and in some cases a necessity, for applying ART for the reproductive and genetic management of CANDES, the challenges encountered with even the most basic procedures have limited the rate of progress. In this foreword we discuss the status of conventional ART, such as artificial insemination and in vitro fertilisation, as well as their benefits and inherent difficulties when applied to CANDES. It is upon these techniques, and ultimately our knowledge of basic reproductive physiology, that the success of emerging technologies, such as those described in this special issue, are dependent for success.

Advanced methods of isolation and identification of porcine primordial follicles

An effective isolation and identification method of primordial follicles would greatly benefit the animal production practice, transgenic animal production and endangered species conservation in the future. This study has not only advanced the isolation method but also developed an identification marker of primordial follicles. After enzymatic digestion, Percoll gradient centrifugation and mesh filtrations, the obtained follicular separations were then subjected to a cell sorter in order to collect primordial follicles. The study greatly improved the yield of primordial follicles (from about 1.85 x 10(5) to 7.79 x 10(5) per prepubertal ovary) by means of increasing cell layer number from 1 ml to 2.5 ml after Percoll gradient centrifugation. Based on traditional morphological criteria, the purity of recovered primordial follicles was averagely about 82.43+/-9.41% (n=5) because of their similar size and appearance with somatic cells. To further exactly appreciate the purity of sorted primordial follicles, a germ cell-specific protein, MSY2, was used to recognize the oocytes of primordial follicles. The results of repeat experiments showed that about 98.31+/-0.73% (n=4) of the primordial follicles cluster was MSY2-positive, which indicated the identification method of primordial follicles was more effective and high-yielded than the previous methods because of its higher purity.

Production of offspring from cryopreserved chicken testicular tissue

Cryopreservation of avian germplasm provides a means of genetic banking for future needs in biological research and animal production. The sperm of birds can be cryopreserved and used to fertilize eggs. However, the fertility of frozen-thawed avian semen is generally much lower than that of mammalian semen and varies among species or among lines, reducing the value of semen for the preservation of genetic resources. In the present study, a simple freezing protocol was used to cryopreserve testicular tissue of day-old chicks, and after subsequent transplantation, the frozen-thawed testicular tissue developed functional seminiferous tubules that produced sufficient sperm to fertilize eggs, resulting in donor-derived offspring. This study provides an alternative to semen cryopreservation for storage of the male germline in birds.

Male-to-male differences in post-thaw motility of rhesus spermatozoa after cryopreservation of replicate ejaculates

BACKGROUND

The efficiency of controlled propagation to produce rhesus monkeys of particular genotypes can be maximized by use of cryopreserved spermatozoa collected from specific males to inseminate appropriate females. But this assumes that semen from males with different genotypes can be cryopreserved with equal effectiveness.

METHODS

To investigate whether spermatozoa from different Macaca mulatta males can be effectively cryopreserved when frozen under identical conditions, we collected and froze semen specimens from 13 adult, fertile males maintained at three primate research centers.

RESULTS

Survival, based on post-thaw motility normalized to the pre-freeze value, was assayed within 30 minutes after thawing; it varied from 50% to 70% but declined thereafter. To examine the response of semen from individual males, we collected and froze three to six ejaculates per male from each of seven males.

CONCLUSIONS

In general, semen from a given male responded reproducibly to freezing, but there were significant differences among males. The cause of these differences among M. mulatta males in post-thaw sperm survival remains unidentified.

Effect of cryopreservation on viability, activation and growth of in situ and isolated ovine early-stage follicles

Isolated or cortical tissue-enclosed (in situ) sheep early-stage follicles were exposed to 1.5 M dimethyl sulfoxide (DMSO), ethylene glycol (EG) or unexposed, or frozen/thawed in the presence of these cryoprotectants and then cultured for 5 days in enriched minimal essential medium (MEM) or not cultured. Cultured and uncultured follicles were classified as non-viable/viable when they were stained/not stained with trypan blue, respectively. Follicular diameter was measured and the percentages of primordial and developing follicles calculated. Exposure of isolated or in situ follicles to DMSO or EG led to a marked decrease in the percentage of viable follicles. The percentage of viable isolated and in situ follicles further decreased when they were in vitro-cultured for 5 days, EG-exposed follicles generally showing a more damaging effect than DMSO-exposed follicles. Cultured follicles, both isolated and in situ, which were exposed to EG and DMSO, as well as in situ follicles, which had been frozen/thawed in the presence of one of these cryoprotectants, showed similar growth rates as cultured, untreated follicles, while in these groups significantly lower percentages of primordial follicles and higher percentages of more advanced follicular stages were observed. Among the treated groups, the highest percentage (71-75%) of developing follicles was observed after culturing cryoprotectant-exposed isolated follicles. In contrast, when cryopreserved, isolated follicles were cultured, they did not increase in diameter and did not develop into more advanced stages. In conclusion, exposure to or cryopreservation in the presence of EG and DMSO, as well as their further in vitro culture, negatively affected the viability of ovine isolated and in situ early-stage follicles. In vitro growth of early-stage follicles and activation of primordial follicles were better maintained when follicles had been frozen/thawed and cultured in situ.