A CompetitiveIn VitroAssay of Human Sperm Fertilizing Ability Utilizing Contrasting Fluorescent Sperm Markers

Successful selection of mouse sperm with high viability and fertility using microfluidics chip cell sorter

Cell sorting via flow cytometry is a powerful tool to select subpopulations of cells in many biological fields. Selection of fertilisation-prone sperm is a critical step to ensure a stable and high fertilisation rate in in vitro fertilisation (IVF). However, a combination of conventional cell sorting and IVF system has not been established because of severe mechanical damages to the sperm during the sorting process. A cell sorter with microfluidics chip technology that lessens cell damage during cell sorting may address this problem. We evaluated the effects of microfluidics chip cell sorting on the sperm using the parameters, such as motility and fertility, and found this cell sorting method had minimal harmful effect on the sperm. Then, sperm were selected by a marker for acrosome reaction and showed higher fertilisation rate than that of the population of acrosome-intact sperm. Embryo derived from these sperm developed normally. These results indicated that microfluidics chip cell sorting can select fertile sperm to improve IVF technique.

Diagnostic significance of sperm-zona pellucida interaction

Spermatozoa binding to the zona pellucida is an early, critical event leading to fertilization and early pre-embryo development. Fertilization involves a complex and orderly sequence of events that is completed at syngamy, which is defined as the union of the two sets of haploid chromosomes to form a new diploid fertilized ovum (zygote). In order to be able to fertilize an oocyte, spermatozoa need to undergo a process called ‘capacitation’, which is usually defined as a series of changes that renders the sperm cells capable of undergoing the acrosome reaction. This process that naturally occurs within the female genital tract is possible under in vitro conditions. However, capacitation is not the only process spermatozoa must undergo to fertilize the oocytes successfully. To fertilize an oocyte, spermatozoa must also be at least highly motile, as well as being capable of undergoing the acrosome reaction timely, penetrating through the oocyte investments and fusing with the oocyte plasma membrane properly.

The application of in vitro sperm competition test to evaluate the impact of ZP-derived peptides on fertilization capacity of cat sperm

The present study aimed to establish a sensitive in vitro assay to assess the binding capacity of cat spermatozoa. Cat oocytes and epididymal sperm cells were isolated from gonads and cultured for in vitro fertilization. Before fertilization, the sperm cells were incubated either in 10 microM green dye Fluo-3-AM or 10 microM orange dye CellTracker Orange CMTMR (Molecular Probes), respectively. After removing the dyes by washing, sperm cells stained with each dye were added to medium drops containing oocytes in various proportions and cultured for 16 h at 37 degrees C, 5% CO(2). The oocytes were examined using fluorescence microscopy. Sperm bound to oocytes, and stained with different colors, were counted. When fresh epididymal sperm were mixed in at a specific proportion, the number of sperm bound to the zona pellucida (ZP) of oocytes reflected the proportion of differently colored sperm in the medium. This indicated that neither dye influenced the binding capacity of cat sperm. Mixing fresh and cryopreserved sperm, however, resulted in a higher number of fresh sperm bound to the oocyte surface in comparison to frozen-thawed sperm. Also, the pre-incubation of cat sperm cells with ZP derived peptide reduced the sperm binding capacity by 40%. In conclusion, the presented sperm competition assay allows assessment of fertilizing capacity of cat spermatozoa in vitro when a mixture of two different populations is used. The applied supravital fluorescence dyes do not affect motility and binding capacity of sperm cells and were clearly distinguishable under fluorescence microscopy. We demonstrate that the assay can be used to study the impact of sperm treatment, such as cryopreservation or pre-incubation in bioactive peptides, on fertilizing capacity.

Identification of embryo paternity using polymorphic DNA markers to assess fertilizing capacity of spermatozoa after heterospermic insemination in boars

Differences in sperm fertilizing capacity of males often remain undetected by routine semen parameters. Heterospermic insemination with equal numbers of spermatozoa from 2 males is an accurate method for assessing differences in fertility. Use of heterospermic insemination depends on a reliable, efficient assay to identify paternity of conceptuses or offspring. In this study, polymorphic DNA markers amplified by PCR were tested to determine paternity of Day 5 to 6 embryos. The fertilizing capacity of 2 boars (A and B) with similar semen parameters was compared after homospermic (n=14 gilts) and heterospermic (n=11 gilts) insemination. Single AI's were performed under suboptimal conditions using 1 x 10(9) spermatozoa at 12 to 24 h before ovulation to prompt differences in fertilization and to stimulate sperm competition. The fertilization rate and the number of accessory spermatozoa were determined in Day 5 to 6 embryos. Using 5 different polymorphic DNA markers, paternity could be determined in 95.8% of the embryos. Boar B sired significantly (P<0.05) more offspring than Boar A after insemination with pooled semen, and this was reflected by a significantly (P<0.05) higher number of accessory spermatozoa following homospermic insemination with semen from Boar B, although fertilization rates did not differ between the 2 boars after homospermic insemination. The results suggest that the viability of spermatozoa in the female reproductive tract contributes to differences in fertility rates of males with similar in vitro sperm quality parameters. The number of accessory spermatozoa is a more sensitive measure of boar fertility than the fertilization rate. Polymorphic DNA markers are suitable for verification of parentage even at a very early stage of embryonic development.

Assessment of the viability and fertilizing potential of cryopreserved bovine spermatozoa using dual fluorescent staining and two-flow cytometric systems

A dual fluorescent staining system utilizing 5 (and-6)-carboxy-4',5'-dimethyl fluorescein diacetate (CDMFDA) and Hydroethidine (HED) was developed to provide quantifiable information reflective of spermatozoal viability and fertilizing potential. Cryopreserved spermatozoa from ten bulls on which there was fertilizing capacity information were incubated for 1.5, and 3 hr at 39 degrees C prior to fluorogenic staining. Spermatozoa were analyzed using both a FACS Analyzer and an EPICS V flow cytometer to determine if a particular fluorescence pattern was due to an instrumental artifact or cellular processes. Five fluorescent cellular populations were identified by the FACS Analyzer and three populations by the EPICS V. Spermatozoa were quantified after each incubation time for red (HED) and green (CDMFDA) fluorescence. Viable spermatozoa retained the greatest amount of both green and red fluorescence. Dead or moribund spermatozoa had a decrease in over-all fluorescence. The number of viable cells at 0 hr plus the number of dead or morbid cells at any time period were identified by the FACS Analyzer as important in estimating the potential fertility of a bull. The EPICS V identified the number of dead or moribund cells as being related to nonreturn rates. Incubation of samples decreased cellular viability, which resulted in reduced levels of both green and red fluorescence. Similarities between data obtained with both flow cytometers illustrated that cellular processes, not instrumental artifacts, were responsible for the decrease in over-all fluorescence when viability declined, the relationship between the number of cells with specific fluorescence levels and nonreturn rates, and the incubative-induced changes in fluorescence patterns.

A human sperm-zona pellucida binding test using oocytes that failed to fertilize in vitro

A test for human sperm binding to the zona pellucida (ZP) was developed using oocytes which failed to fertilize in vitro. Heterospermic insemination with equal numbers of test and fertile donor sperm differentially labeled with fluorescein isothiocyanate or tetra-methylrhodamine B isothiocyanate controlled for variability in ZP-sperm binding capacity. The number of sperm bound to the ZP was independent of previous sperm binding in in vitro fertilization (IVF), preservation of the ZP in salt solution, and fluorochrome labeling but increased linearly with time and sperm concentration. Sperm from men who had one or more failed attempts at IVF with no or few oocytes fertilized usually displayed very low ZP binding ratios of test to normal sperm. This test may predict the ability of sperm to fertilize human oocytes in vitro and should be useful in studies of human gamete interaction.

Capacitation and acrosome reactions in human spermatozoa monitored by a chlortetracycline fluorescence assay

Human spermatozoa were incubated in culture medium containing human serum albumin (HSA) to promote capacitation, which was monitored by a rapid chlortetracycline (CTC) fluorescence assay. Four CTC fluorescence patterns were readily distinguished, one of which appeared to be correlated with capacitated sperm. When capacitated sperm were treated with either ionophore A23187 or acid-solubilized mouse zonae pellucidae to induce the acrosome reaction, the CTC assay identified acrosome-reacted sperm by lack of fluorescence on the head. Fresh sperm would not undergo the induced acrosome reaction. The percentages of acrosome-reacted sperm identified by the CTC assay in induced and control populations were the same as those identified by the presently used indirect immunofluorescence and triple stain assays.

Homospermic versus heterospermic insemination of zona-free hamster eggs to assess fertility of fluorochrome-labeled acrosome-reacted bull spermatozoa

Fresh spermatozoa from six bulls, with fertility ranging from 64% to 78%, (based upon 59-day nonreturn rates for 159,448 cows inseminated) were mixed with zona-free hamster eggs in 15 heterospermic pair inseminations. Five of the bulls were used in homospermic insemination studies. Prior to incubation, spermatozoa from each bull were labeled with contrasting fluorescent stains pretested for effects on spermatozoa. Equal numbers of spermatozoa were mixed and treated with liposomes of dilauroylphosphatidylcholine to induce the acrosome reaction. Spermatozoa from split ejaculates within a male competed against each other equally in the hamster egg test, indicating that the staining procedure did not affect egg penetration rates. Bulls differed in their egg penetration rates when their sperm were inseminated either homospermically or heterospermically, but the differences in the homospermic inseminations were not significantly correlated with sire fertility. The number and percentage of sperm which penetrated eggs, and the number of eggs penetrated in the heterospermic competitive tests were highly correlated with fertility (r greater than or equal to 0.86). Therefore, egg penetration rates from heterospermic inseminations appear to be valuable indicators of fertility and much more sensitive predictors than results from homospermic inseminations.

In vitro fertilization and embryo transfer in domestic animals: applications in animals and implications for humans

Extensive research has been conducted in domestic animals, particularly in cattle, in the reproductive technologies of sperm handling, capacitation, and acrosome reaction, superovulation, and embryo handling, sexing, bisection, cryopreservation, and transfer. Because of the economic importance of cattle these technologies have been tested and improved under clinical conditions. The results of employing these procedures are available on tens of thousands of pregnancies and offspring. This information has implications in applying some of the same technologies in human reproduction. The large number of normal progeny produced in cattle after a long prenatal development period, similar to humans, provides some assurance that these technologies, carefully applied, are safe. The basis for these conclusions is documented in the publications cited in this review.

Human sperm function in the ejaculate following vasectomy

Semen specimens were obtained for analysis from nine men immediately before vasectomy and 3 days following the vasectomy procedure. After vasectomy there was a significant decrease in seminal sperm concentration, percentage of sperm motility, and mean swimming speed. In seven of nine cases the spermatozoa did not survive overnight incubation in capacitation media, and in no case was penetration of zonafree hamster oocytes observed 3 days after vasectomy.

What functions of the sperm cell are measured by in vitro fertilization of zona-free hamster eggs?

Human spermatozoa were capacitated in media containing either high concentrations (3.5%) of human serum albumin (HSA) or low concentrations (0.3%) of bovine serum albumin (BSA). The effects of both capacitation media were assessed immediately and after overnight preincubation (18 to 24 hours) by adding a mixture of nonliving human oocytes and living zona-free hamster eggs to the sperm suspension. Overnight preincubation of sperm in media containing 3.5% HSA enhanced sperm fusion with hamster vitelli, but the capacity for zona penetration was lost. These effects could be attributed to the concentration of HSA rather than a general effect of albumin concentration, because overnight preincubation in 3.5% BSA did not interfere with zona penetration. During overnight incubation in 3.5% HSA, the percentage of acrosome reactions increased, as did alterations in the equatorial segment of the acrosome-reacted sperm. The percentage of motile sperm remained high after overnight incubation in 3.5% HSA, but both the mean swimming speed and flagellar activity on the zona surface declined. The sperm also lost their ability for strong zona binding after overnight incubation in 3.5% HSA.

Heterologous ovum penetration test and seminal parameters in fertile and infertile men

Sperm penetration rates in the heterologous ovum penetration test were correlated with results of routine semen analysis in 30 fertile and 50 infertile men. There was no difference in penetration rates when comparing infertile men with normal and abnormal seminal parameters, nor was any difference seen between fertile (15-83%) and infertile men (8-83%). Of the 22 infertile men with normal seminal characteristics, seven had partners with no discernible reproductive dysfunction. The penetration rates of these men (38-81%) did not differ from those of fertile men. Stepwise regression analysis of seminal characteristics, with penetration as the dependent variable, indicated that sperm count and morphology are the most important seminal parameters for fertility assessment. Discrimination analysis revealed that sperm numbers and morphologic variables provide significant information for discriminating between fertile men and infertile men with normal or abnormal seminal characteristics. Sperm penetration and motility were not indicated as important factors. The present data suggest that, in unselected male patients seeking reproductive evaluation, the sperm penetration assay did not yield any additional information on the cause of infertility.

Human sperm penetration of zona-free hamster eggs after storage of the semen for 48 hours at 2 degrees C to 5 degrees C

The motility of human spermatozoa and their ability to penetrate zona-free hamster eggs were examined after dilution of the semen with TES-Tris (TEST) yolk buffer and storage for 48 hours at 2 degrees C to 5 degrees C. Semen samples from 10 fertile donors and 19 infertility patients were studied. More than 65% of the spermatozoa which were initially motile in the TEST yolk buffer remained active after storage. During storage, the mean swimming speed of the sperm declined to approximately 60% of the prestorage value. The percentage of zona-free hamster eggs that were penetrated by spermatozoa from patients and donors increased significantly following 48 hours of storage at 2 degrees C to 5 degrees C. Normal semen and abnormal semen were equally preserved by this storage method. This procedure may be used to ship semen samples by commercial transportation to specialized laboratories for testing. Low temperature storage in the TEST yolk buffer appears to enhance the fertilizing capacity of human spermatozoa in vitro.