Hoechst staining and exposure to UV laser during flow cytometric sorting does not affect the frequency of detected endogenous DNA nicks in abnormal and normal human spermatozoa

Recombinant Staphylococcal Enterotoxin Type A Stimulate Antitumoral Cytokines

BACKGROUND

About 20 different types of staphylococcal enterotoxins are produced by Staphylococcus aureus, in which type A is more common in food poisoning syndrome. Also staphylococcal enterotoxin A superantigen is a potent inducer of cytotoxic T lymphocyte activity and cytokine production and could stimulate T cells containing T-cell receptor beta chain domains when binding to major histocompatibility complex class II molecules. Hence, it is an important reagent in cancer immunotherapy.

METHODS

For the construction of pET-21a/ entA cassette, the staphylococcal enterotoxin type A gene was isolated from S aureus strain HN2, cloned into pET-21a, and introduced into Escherichia coli strain BL-21(DE3). Consequently, Western blot analysis showed pET-21a/ entA cassette expression inserted entA gene successfully. It is the first prompt using a pET-21a as a cloning vector for entA gene and expression of construct in BL-21(DE3). In addition, this study examined the ability of standard staphylococcal enterotoxin A and cloned staphylococcal enterotoxin A to activate T cells in vitro. Lymphocyte cells derived from lymph node BALB/c mice were exposed to standard staphylococcal enterotoxin A and cloned staphylococcal enterotoxin (1.10, 102,103, and 104 ng/µL) in order to evaluate the magnitude of proliferation, activation, and apoptosis of lymphocyte cells based on MTT and apoptosis assays, respectively.

RESULTS

Our investigation showed that the function of cloned staphylococcal enterotoxin A was same as standard staphylococcal enterotoxin A, and the optimal concentration for the activation of lymphocyte cells and induction of apoptosis was 100 ng/µL and 1000 ng/µL ( P < .05), respectively. Quantification of cytokines clearly showed that lymphocyte cells exposed to standard staphylococcal enterotoxin A and cloned staphylococcal enterotoxin A significantly secreted higher interferon γ and tumor necrosis factor α compared to control.

CONCLUSION

According to our results, the biological activity of standard staphylococcal enterotoxin A and cloned staphylococcal enterotoxin A is identical; therefore, these procedures may be approved as an efficient method to express and purify this protein in a large scale.

High-resolution melt analysis does not reveal mutagenic risk in sexed sperm and in vitro-derived bovine embryos

The objectives of the present work were to verify whether simultaneous exposure to Hoechst 33342 and UV irradiation during sorting by flow cytometry may induce gene point mutations in bovine sperm and to assess whether the dye incorporated in the sperm may imply a mutagenic effect during the embryonic development. To this aim, high-resolution melt analysis (HRMA) was used to discriminate variations of single nucleotides in sexed vs. non-sexed control samples. Three batches of sorted and non-sorted commercial semen of seven bulls (42 samples) were subjected to HRMA. A set of 139 genes located on all the chromosomes was selected, and 407 regions of the genome covering a total of 83 907 bases were analyzed. Thereafter, sperm of one sexed and one non-sexed batch of each bull was used in in vitro fertilization, and the derived embryos were analyzed (n = 560). One hundred and thirty-three regions of the bovine genome, located in 40 genes, were screened for a total coverage of 23 397 bases. The comparison between the frequencies of variations, with respect to the sequences deposited, observed in the sexed and non-sexed sperm (843 vs. 770) and embryos (246 vs. 212) showed no significant differences (P > 0.05), as measured by chi-square tests. It can be concluded that staining with Hoechst 33342 and exposure to UV during sorting does not lead to significant changes in the frequencies of variants in the commercial sexed semen and in embryos produced in vitro with the same treated sperm.

Developmental kinetics and gene expression in male and female bovine embryos produced in vitro with sex-sorted spermatozoa

Using bovine embryos generated in vitro from IVF with X-sorted, Y-sorted and unsorted spermatozoa, we compared the kinetics of male and female embryo development and gene expression between male and female blastocysts. Bovine in vitro-matured oocytes (n = 8858) were fertilised with spermatozoa from each of three different bulls (X-sorted, Y-sorted or unsorted spermatozoa depending on the experiment). The cleavage rate was assessed 24, 27, 30, 33, 36, 40, 44 and 48 h post insemination (h.p.i.) and blastocyst development was recorded on Days 6-9. The relative mRNA abundance of nine genes (GSTM3, DNTM3A, PGRMC1, TP53, BAX, COX2, IGF2R, AKR1B1 and PLAC8) was analysed in male and female Day 7 blastocysts produced with sorted and unsorted spermatozoa from one bull. Cumulative cleavage rate and blastocyst yield were significantly higher in the unsorted group compared with the X- or Y-sorted group from the same bull (P < or = 0.05). Although differences existed between bulls in terms of cleavage rate, no differences were observed in cleavage rate between X- and Y-sorted spermatozoa within a bull. The blastocyst yield was significantly higher only for Bull 3 when the Y-sorted spermatozoa were used (27.1+2.8 v. 19.1+1.4 for Y- and X-sorted spermatozoa, respectively; P < 0.05). There were no differences in the mRNA abundance of the nine genes analysed between embryos of the same sex produced with sorted or unsorted spermatozoa. However, significant differences in polyA mRNA abundance were observed between male and female blastocysts for three genes (GSTM3, DNMT3A and PGRMC1; P < or = 0.05). In conclusion, the use of sorted rather than unsorted spermatozoa in IVF significantly delays the onset of first cleavage. Differences were noted between bulls, but not between X- and Y-sorted spermatozoa, and although no differences were found in terms of the mRNA abundance of the nine genes tested between sorted and unsorted spermatozoa, sex-related differences were found in the case of three genes.

Improved quality of sex-sorted sperm: a prerequisite for wider commercial application

To date the only successful method to sort sperm into X- and Y-chromosome-bearing populations is the Beltsville Sperm Sexing Technology. Fertility results continue to be variable even though the technology has been used in a commercial setting for nearly a decade. This is at least partly due to the reduced lifespan of sperm after sorting and freezing. Several technical and biological factors are responsible for this problem. Furthermore, to meet economic demands, only 10-15% of the number of sperm (compared to unsexed semen) are loaded in each straw, further limiting the chances for fertilization. A new protocol for preservation of bull sperm, utilizing Sexcess shows promise in extending the lifespan of sorted bull sperm. Motility and acrosome integrity are significantly increased using Sexcess. Conception rates achieved with heifers for those bulls tested with Sexcess and using a standard AI regime give results that do not differ from results achieved using regular AI. In addition to the improvements of the sorting technology itself, we recommend a thorough pre-selection of bulls. A reliable prediction method to determine whether a bull is suitable for a sex-sorting program still does not exist. Such a test is needed, especially for "custom sorting" programs. Currently, test sorts are the only means of obtaining information about the sorting efficiency of semen from a particular bull.

Effects of cryopreservation on semen quality and the expression of sperm membrane hexose transporters in the spermatozoa of Iberian pigs

This study evaluated the effects of cooling, freezing and thawing on the plasma membrane integrity, kinetics and expression of two sugar transporters glucose transporter-3 and -5 (GLUT-3 and GLUT-5) in spermatozoa from Iberian boars. Semen samples were collected twice weekly from eight young, fertile Iberian boars of the 'Entrepelado' and 'Lampiño' breeds. The samples were suspended in a commercial extender and refrigerated to 17 degrees C for transport to the laboratory (step A), where they were further extended with a lactose-egg yolk-based extender and chilled to 5 degrees C (step B) prior to freezing in the presence of glycerol (3%). Spermatozoa were assessed for plasma membrane integrity and sperm motility at each of the steps, including post-thaw (step C). Aliquots were also prepared for immunocytochemical localisation of the sugar transporters (fixed and thin smears for transmission and scanning electron microscopy levels respectively) and for SDS-PAGE electrophoresis and subsequent western blotting, using the same antibodies (rabbit anti-GLUT-3 and anti-GLUT-5 polyclonal antibodies). The results showed lower percentages of progressively motile spermatozoa at step C in both breeds, while the percentage of live spermatozoa was significantly lower only in the 'Entrepelado' breed. The results obtained from electron microscopy clearly showed that Iberian boar spermatozoa expressed the hexose transporters, GLUT-3 and GLUT-5. The pattern of expression, in terms of location and concentration, was characteristic in each case but, in the case of isoform GLUT-5, it remained constant during the different steps of freezing-thawing protocol. These results indicate that cryopreservation affects the status of sperm cells of Iberian boars by altering the distribution of some membrane receptors and decreasing the percentage values of parameters linked to sperm quality.

Altered mRNA expression patterns in bovine blastocysts after fertilisation in vitro using flow-cytometrically sex-sorted sperm

Sperm-sexing has been used to produce embryos and offspring of a pre-determined sex in a number of species. However, the fertility of sex-sorted sperm is reduced and the full effects of sperm-sexing remain to be elucidated. The purpose of the present study was to investigate the potential effects of sex-sorted sperm on mRNA expression patterns of developmentally important genes employing in vitro produced bovine embryos. Bovine embryos were produced in vitro with unsorted and sex-sorted sperm and mRNA expression patterns were determined for glucose-3 transporter (Glut-3), glucose-6-phosphate dehydrogenase (G6PD), X-inactive specific transcript (X-ist) and Heat shock protein 70.1 (Hsp) using semi-quantitative endpoint reverse transcriptase-PCR in male and female, day-7 and 8 embryos. The relative abundance (RA) of Glut-3 was higher for day-7 male than female embryos, and day-7 embryos derived from unsorted compared with sex-sorted sperm. The RA of G6PD was higher for embryos derived from unsorted than sex-sorted sperm, and for day-8 female compared with male embryos. The RA of Xist was higher for female than male embryos, and for day-7 female embryos derived from unsorted than sex-sorted sperm. Hsp RA was higher for female compared with male embryos, was similar for day-7 and 8 embryos, and unsorted and sex-sorted sperm derived embryos. These results demonstrate differential expression of developmentally important genes between male and female embryos, and embryos derived from unsorted and sex-sorted sperm.

Challenges facing sex preselection of stallion spermatozoa

Since the production of the first live offspring from sex-sorted spermatozoa in 1989, there have been many developments in the fluorescence-activated cell separation (FACS) procedures to preselect X- and Y-chromosome bearing spermatozoa prior to insemination. During this time, FACS technology has been applied to a range of species and has resulted in offspring from rabbits, cattle, sheep, elk and horses. In horses, satisfactory fertility rates have been achieved after hysteroscopic insemination of 20 x 10(6) fresh or stored, sex-sorted spermatozoa. However, many of the sperm processing protocols are still based on the original protocol and components of these procedures may not necessarily be suitable for the stallion. This review examines the details of FACS protocols that have resulted in the production of live offspring and makes comparisons with the published stallion protocols in an attempt to determine how best to improve the fertility of sorted, frozen-thawed stallion spermatozoa.

DNA integrity in sexed bull sperm assessed by neutral Comet assay and sperm chromatin structure assay

During the production of sex-sorted spermatozoa from bull semen, the cells are exposed to a number of potential hazards including: dilution, centrifugation, incubation, exposure to DNA stains and laser light. These factors may affect the survival capacity and fertilization potential of the sperm. The objective of this study was to determine whether sex-sorted bull spermatozoa have more DNA damage than sperm from conventional processed bull semen. Two methods were used to determine DNA integrity: the neutral Comet assay (NCA) and the sperm chromatin structure assay (SCSA). The NCA showed that the conventional samples had a higher tail moment (TM) (P < 0.017) than the sorted samples and that there was no difference between the samples in tail length (TL) (P = 0.36). The SCSA showed that the DNA fragmentation index (DFI) was higher for conventional than the sorted samples (P = 0.011), but the standard deviation of DFI (SD-DFI) was higher for the sorted samples (P < 0.001). We conclude that the NCA and SCSA can be used in assessing DNA integrity in bovine sperm and that cell sorting by flow cytometry improves the integrity of the sperm cell population. Additionally the results from the SCSA indicated that the sex-sorted sperm had less homogenous sperm chromatin. In the future assessment of sperm DNA integrity may be used to select bulls for sperm sex sorting and optimizing sperm sex sorting procedures.

Flow cytometric evaluation of sperm parameters in relation to fertility potential

Most laboratory methods used to evaluate semen quality have not correlated highly with fertilizing capacity. The discovery of a variety of fluorochromes and compounds conjugated to fluorescent probes has enabled a more widespread analysis of sperm attributes, and in conjunction with the flow cytometer, permit the evaluation of a large number of spermatozoa. A number of characteristics of sperm integrity, viability and function can be assessed by flow cytometry. The DNA status of spermatozoa has been determined using the metachromatic properties of acridine orange (AO). AO staining, when used in the sperm chromatin structure assay (SCSA), correlates with fertility in a number of species. DNA fragmentation can also be assessed using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, which identifies DNA strand breaks by labeling free 3'-OH termini with modified nucleotides. The status of the sperm acrosome can be determined using fluorescently labeled lectins and LysoTracker Green DND-26, a fluorescent acidotropic probe. Capacitation status has been observed through calcium-mediated changes using chlortetracycline (CTC) or by changes in membrane fluidity monitored by the binding of the fluorescent amphiphilic probe, Merocyanine 540. Fluorescently labeled annexin-V, C6NBD and Ro-09-0198 can also be used to detect changes in membrane phospholipid distribution. Cell viability can be determined using the propensity of propidium iodide (PI), ethidium homodimer-1 (EthD-1) or Yo-Pro-1 to permeate damaged membranes. These are generally more adaptable to clinical flow cytometry than the bisbenzimide membrane impermeable stain, Hoechst 33258, which excites in the ultraviolet range and requires UV laser equipment. Mitochondrial function can be determined using rhodamine 123 (R123) and MitoTracker Green FM (MITO) and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1). Flow cytometry is a tool that may be used in the future to monitor many new potential markers of sperm function.

Integration of sperm sexing technology into the ART toolbox

Sex-sorting of mammalian spermatozoa has applications for genetic improvement of farm animals, in humans for the control of sex-linked disease, and in wildlife as a captive management strategy and for the re-population of endangered species. Considerable research has been undertaken worldwide on the Beltsville sperm sexing technology, the only effective method for pre-selection of sex of offspring. The combination of this method with assisted reproductive technologies has resulted in the birth of offspring in a wide range of animals, including cattle, the only livestock species in which sperm sexing is used commercially. Major improvements in the efficiency of sorting, in particular the development of high speed sorting (15 million X and Y spermatozoa per hour) have led to the production of offspring using conventional and low dose AI and the successful cryopreservation of sorted spermatozoa in cattle, sheep, horses and elk. A major limitation remains the short viable lifespan of sorted spermatozoa in the female genital tract, in most species necessitating sperm deposition deep in the uterus, and close to the expected time of ovulation, for acceptable fertility after in vivo insemination. Special deep uterine insemination technology has been employed to produce offspring in pigs and horses using low sperm doses. Considerable attention has been paid to reduction of the damage and capacitation-like changes to spermatozoa that result from flow cytometric sorting and from freezing and thawing. However, high-purity sorting of liquid-stored or frozen-thawed spermatozoa for immediate use, or re-cryopreservation for later use, does not reduce its fertilizing capacity in vitro, allowing its combination with in vitro fertilization or juvenile in vitro embryo transfer to produce blastocysts, and offspring in sheep and cattle after embryo transfer. Further research into sorting and preservation methods that incorporate strategies to prevent destabilization of sperm membranes may improve the fertilizing lifespan of flow cytometrically sorted spermatozoa. With continued improvement in sorting instrumentation and biological handling, sorting efficiency should reach a point where commercially acceptable pregnancy rates may be achieved in a number of species after conventional or deep uterine insemination.

Preservation and artificial insemination of sexed semen in sheep

Sperm-sexing technology using flow cytometry is in advanced stages of development for the sperm of several species. The sorting process could compromise sperm viability and sperm require specific handling procedures both before and after sorting to maintain the integrity and function of the sorted sperm. Standard freezing protocols have been modified for post-sorting cryopreservation of sperm and frozen sperm have been successfully thawed, sorted, refrozen and subsequently used to produce offspring. The relatively low numbers of available sorted sperm have, in some cases, led to modification of artificial insemination techniques to maximise efficiency of use. Multiple ovulation and embryo transfer, or in vitro fertilisation and associated technology, may lead to the more efficient use of sexed sperm.

Cross-linking of histone proteins to DNA by UV illumination of chromatin stained with Hoechst 33342

The photochemical effects of near-UV light on chromatin labeled with the vital DNA dye Hoechst 33342 (H33342) are studied. Several types of experiments demonstrate that illumination at both 365 and 410 nm results in significant cross-linking of proteins with the DNA. Fluorescence microscopy of dye-stained Xenopus XTC-2 nuclei shows that UV illumination has effects similar to chemical fixation by formaldehyde. At 365 nm a dose of approximately 70 J/cm2 results in 50% of the DNA being cross-linked, as measured by chloroform-sodium dodecyl sulfate extraction. At 410 nm the efficiency of cross-linking was smaller by a factor of 3. Gel electrophoresis of the cross-linked proteins shows them to be predominantly core histones. The implications of these results for experiments on live cells stained with H33342, for example, fluorescence microscopy of nuclear dynamics or cell sorting, are discussed.

In vitro and in vivo assessment of functional capacity of flow cytometrically sorted ram spermatozoa after freezing and thawing

The effect of sex sorting and freeze–thawing on the viability and fertility of ram spermatozoa was investigated in the present study. Non-sorted (control) frozen–thawed spermatozoa had a higher motility and forwards progressive motility (FPM) than sorted frozen–thawed spermatozoa (60.9 ± 2.9% v. 57.0 ± 3.3% and 4.0 ± 0.1 v. 3.5 ± 0.1 FPM, respectively; P < 0.001) after incubation (6 h at 37°C). Sorted and non-sorted (control) frozen–thawed spermatozoa had similar acrosome integrity (73.7 ± 1.8% v. 75.2 ± 2.1%, respectively) after thawing and incubation. A greater proportion of sorted spermatozoa displayed chlortetracycline staining patterns that were characteristic of capacitation (22.0 ± 2.8%; P < 0.05) than non-sorted (control) spermatozoa (15.4 ± 2.6% B pattern) before freezing. Overall, more sorted frozen–thawed spermatozoa showed patterns characteristic of being acrosome reacted (12.8 ± 0.7%; P < 0.01) and less were uncapacitated (35.5 ± 0.6%; P < 0.05) than non-sorted (control) frozen–thawed spermatozoa (7.7 ± 0.8% and 38.6 ± 0.6% for AR and F pattern, respectively). Similar numbers of non-sorted (control) and sorted frozen–thawed spermatozoa migrated through artificial cervical mucus after 1 h (76.4 ± 11.9 v. 73.9 ± 11.9 spermatozoa, respectively). The distance travelled by the vanguard spermatozoon was also similar (56.9 ± 7.8 v. 38.6 ± 5.8 mm for control and sorted spermatozoa, respectively). Sorted and control frozen–thawed spermatozoa displayed a similar pattern of binding to, and release from, an oviduct epithelial cell monolayer (OECM), but sorted frozen–thawed spermatozoa were released more rapidly (P < 0.05) than non-sorted (control) frozen–thawed spermatozoa. The pregnancy rate was higher for ewes inseminated with 100 × 106 (commercial control) frozen–thawed spermatozoa (59%) than for 5, 10, 20 and 40 × 106 total sorted frozen–thawed spermatozoa (41% overall; P < 0.001). Insemination of 16 × 106 resulted in a higher pregnancy rate (31%) than 106 (17%; P < 0.05), but was similar to ewes that received 4 × 106 sorted frozen–thawed spermatozoa (24%). Time of insemination (54, 58 and 62 h after sponge removal) had no effect on pregnancy rate. Pregnancy in gonadotrophin-releasing hormone-treated ewes was affected by insemination dose (P < 0.05) but not sperm type (sorted and non-sorted) or ram. Pregnancy was higher after insemination of 40 × 106 than 5 or 20 × 106 non-sorted (control) or sorted frozen–thawed spermatozoa (70%, 33% and 35%, respectively; P < 0.05). Sorted frozen–thawed spermatozoa may have a shorter viability within the female tract than non-sorted frozen–thawed spermatozoa.

Motility characteristics and fertilizing capacity of boar spermatozoa stained with Hoechst 33342

Flow cytometry sorting of spermatozoa using fluorescence dye Hoechst 33342 is the only effective sex selection methodology validated in numerous laboratories. This study was carried out to determine the effect of Hoechst 33342 on the motility and fertility of stained boar spermatozoa. Experiment 1 evaluated motility parameters (percentage of motile spermatozoa, velocity, angularity and oscillation) of boar spermatozoa stained with Hoechst 33342 by a computer-aided sperm analysis (CASA) instrument. Spermatozoa (30 million/ml) were divided into five treatment groups and stained during 1 h at 35 degrees C with 9, 18, 27, 60 and 90 microM of H33342. There were no differences in sperm motility patterns nor percentages of motile spermatozoa incubated in the presence of 9, 18 or 27 microM. Percentage of motile spermatozoa and motility parameters decreased significantly (p < 0.05) at 60 microM of Hoechst 33342. Spermatozoa were immotile at concentration of 90 microM. In experiment 2, pregnancy rates, farrowing rates and litter size from sows (n = 275) artificially inseminated (AI) with either Hoechst 33342 stained (27 microM) or unstained (control) spermatozoa were determined. Sows inseminated with stained spermatozoa had no significant lower pregnancy rate (88.33%) as compared with controls (90.32%). Staining neither affected farrowing rates (85.0 vs 87.7%) nor total number of piglets born (10.56 +/- 0.32 vs 10.47 +/- 0.24, stained and controls, respectively). No phenotypical abnormalities were registered among the newborn piglets. The data suggest that incubating spermatozoa with Hoechst 33342 at levels required for X- and Y-bearing chromosome sperm sorting, does not impair sperm viability or their fertility after AI.

Gender selection: ethical, scientific, legal, and practical issues

PURPOSE

This work offers an overview of the technology available and assisted reproductive technology (ART) practitioner attitudes to human reproductive sex preselection in either sperm with the use of flow cytometry (FC) or in embryos by means of preimplantational genetic diagnose (PGD) together with an analysis of Spanish legal environment.

METHODS

A review of the legal, ethical and technical literature of the methods to select the sex in the offspring is performed.

RESULTS

Sex selection in humans has different utilities to be employed depending on each country's law. Moreover, different ethical concerns are raised depending on the type of sex selection, in sperm or embryos. Both methodologies to pre-select the sex are trustworthy, with a high predictive power in the determination of the sex, but nevertheless, PGD is better than FC selection in this aspect.

CONCLUSIONS

After a careful analysis of ethical, legal, and scientific features of gender selection, FC combined with PGD appears to be the most acceptable way to select the sex of the progeny whatever the circumstances are.

Cryopreservation of flow-sorted bovine spermatozoa

Experiments were designed to maximize sperm viability after sorting by flow cytometry and cryopreservation. Experiments concerned staining sperm with Hoechst 33342 dye, subsequent dilution, interrogation with laser light, and postsort concentration of sperm. Concentrating sorted sperm by centrifugation to 10 to 20 x 10(6) sperm/ml reduced adverse effects of dilution. Exposing sperm to 150 mW of laser light resulted in lower percentages of progressively motile sperm after thawing than did 100 mW. Sorted sperm extended in a TRIS-based medium had higher postthaw sperm motility after incubation for 1 or 2 h than sperm extended in egg-yolk citrate (EYC) or TEST media, and equilibrating sperm at 5 degrees C for 3 or 6 h prior to freezing was superior to an equilibration time of 18 h. For sorting sperm 4 to 7 h postcollection, it was best to hold semen at 22 degrees C neat instead of at 400 x 10(6)/ml in a TALP buffer with Hoechst 33342. Current procedures for sexing sperm using flow cytometry result in slightly lower postthaw motility and acrosomal integrity compared to control sperm. However, this damage is minor compared to that caused by routine cryopreservation. Fertilizing capacity of flow-sorted sperm is quite acceptable as predicted by simple laboratory assays, and sexed bovine sperm for commercial AI may be available within 2 years.