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We previously established that levels of the sperm membrane protein, SP22, are highly correlated with the fertility of sperm from the cauda epididymidis of rats exposed to both epididymal and testicular toxicants, and that a testis-specific SP22 transcript is expressed in postmeiotic germ cells. In this study, polyclonal and monoclonal antibodies were generated to study the expression of SP22 in the testis and epididymis, and to determine whether SP22 plays a coincidental or causal role in fertility. Polyclonal antiserum was raised in sheep against full-length recombinant rat SP22 (rSP22). Hybridoma clones were generated from mice immunized with rSP22 and boosted with native SP22; positive clones were used for ascites production. Immunoblots indicated that affinity-purified anti-rSP22 immunoglobulin (Ig) and ascites Ig recognized denatured and native SP22, respectively. Linear epitope mapping of the 189-amino acid SP22 sequence revealed 3 distinct peptide sequences recognized by anti-rSP22 Ig, and 1 sequence recognized by ascites Ig. Cytoplasm of round spermatids and heads of elongating/elongated spermatids immunostained with both anti-rSP22 and ascites antibodies. Isolated rete testis sperm revealed discrete staining over the cytoplasmic droplet, whereas staining was apparent over the equatorial segment of the head by the time sperm reached the caput epididymidis. Clear cells were, interestingly, immunostained along the length of the epididymis. Ascites Ig and anti-SP22 Ig each recognized the equatorial segment of sperm heads from rat, hamster, bull, rabbit, and human. Ascites Ig and affinity-purified anti-rSP22 Ig each significantly inhibited the fertility of cauda epididymal sperm from the rat in vivo, as well as the fertilization rates of cauda epididymal sperm in vitro. Moreover, affinity-purified anti-rSP22 significantly inhibited in vitro fertilization of both zona-intact and zona-free hamster oocytes, suggesting that SP22 may play a role in both the zona penetration and membrane fusion steps of fertilization.

We report 2 novel approaches using flow cytometry to measure intracellular calcium concentration and plasma membrane potential in human spermatozoa. Both approaches have the potential to measure different responses in subpopulations of cells, which is particularly useful when studying heterogeneous populations such as human spermatozoa. Intracellular calcium concentration ([Ca2+]i) was measured using the probe indo-1/AM. This allowed measurements to be made that were independent of variation in cell size and dye loading. It also enabled dead cells to be directly identified and excluded from the analyses without the need for counterstaining. Mean basal [Ca2+]i was determined as 50 nM (25-75 nM range) and, in response to the agonist progesterone (20 microM), this increased transiently to 195 nM (125-285 nM range) before declining to approximately half the maximal level within 2 minutes (values in parentheses correspond to the range of values typically found within a sperm population from 1 sample). These results are comparable with previously published data on whole sperm populations. Sperm membrane potential (VM) was assayed using the probe DiOC6(3). In carefully controlled experiments, a marked depolarization of the plasma membrane potential of capacitated spermatozoa was observed in response to progesterone (20 microM). Following in vitro capacitation, the sperm plasma membrane potential became hyperpolarized compared with the noncapacitated state. Therefore, this technique may be used to assay for sperm capacitation in vitro.

Two fertility trials were undertaken to evaluate the relationship between boar semen quality and fertility (conception rate and litter size) after on-farm artificial insemination (AI). Trial 1 included 98 ejaculates from 27 boars, and trial 2 included 72 ejaculates from 26 boars. The semen quality was measured by computer-assisted semen analysis (CASA) using the Hobson Sperm Tracker. Boar semen was diluted in a standard extender (Beltsville Thawing Solution, BTS), dispensed into 75 ml allquots each containing 1.5 x 10(9) spermatozoa and dispatched to farms by overnight mail for use by their normal AI procedures. Randomly selected 75 ml aliquots of semen from each boar were also sent to the institute of Zoology for CASA measurement. Prior to CASA analysis, the spermatozoa were recovered from the BTS using Percoll gradients, resuspended in trisbuffered saline media containing 40 mM Ca++, and incubated at 39 degrees C. Parameters of sperm motion were measured after 0, 2, 4, and 6 hours of incubation. Various multiple regression models based on measured motion parameters could account for up to 24% of the variation in litter size. Using logistic regression, highly significant (P < 0.0001) models explaining conception rate in terms of sperm motion were derived for trial 2 only. The change in sperm velocity during the first 2 hours of incubation and the magnitude of the velocity parameters after 2 hours were identified as the most consistent indicators of fertility. Other attributes of sperm quality, i.e., frequency of spontaneous acrosome reactions (AR) and ARs induced by ionophore A23187 or solubilized pig zona pellucida, were also examined. When the "within-trial" median litter size was used as a way of allocating ejaculates to "high" or "low" litter-size groups, higher litter size was associated with lower frequency of both spontaneous and induced AR. These results demonstrate that fertility information can be derived from the CASA analysis of boar semen provided it is combined with a period of incubation in capacitating conditions.

Cryomicroscopy has enabled direct observation of freezing and thawing of human spermatozoa. When used with a fluorescent viability kit, sperm membrane damage was not apparent down to temperatures of -5 degrees C, but significant damage occurred after thawing (55% of spermatozoa had damaged membranes). Semen samples were cooled or frozen to temperatures (at decrements of 10 degrees C) from 0 degree C to -110 degrees C. At all these temperatures the proportion of live to membrane-damaged cells remained constant. Samples held at temperatures above -30 degrees C were not adversely affected. Below -30 degrees C there was a gradual increase in the proportion of membrane-damaged cells on thaw and a decrease in the number of live cells recovering motility. At temperatures between -50 degrees C and -60 degrees C there was an equal proportion of live motile, immotile, and membrane-damaged cells. It is concluded that some irreversible damage to spermatozoa was a result of freezing processes in cells frozen to -30 degrees C or less, but most of the cryodamage was incurred during thawing, possibly due to recrystallization.

The performance of a computer-assisted semen analysis system was evaluated for use with washed boar spermatozoa. Accuracy was tested using a computer graphics-generated series of spots moving along horizontal, vertical, and diagonal paths, with both straight and sinusoidal trajectories. Observed and expected values agreed to better than +/- 5%, and there was exact agreement in many cases. Reproducibility was tested by making 10 measurements of a single prerecorded sequence of boar spermatozoa. Coefficients of variation were < 3% for all sperm motion parameters tested. Setup conditions affecting the sample statistics of sperm populations were examined. Search radius (10 settings) and minimum track point (10 settings) were varied factorially to evaluate their biasing effects upon population sampling and accuracy. Low search radius (< 12 microns) or high minimum track point values (> 26 frames) precluded measurements of rapidly moving cells and thus led to selection of slow-moving cells. High search radius (> 16 microns) and low minimum track point settings (< 22 frames) led to erroneous tracking and poor data quality. Suitable settings for these setup parameters (search radius = 13 microns; minimum track points = 24) were chosen for use in subsequent fertility trials because they caused the least sampling bias.

Rat spermatozoa recovered from different regions of the excurrent ducts of 10 adult males (proximal cauda epididymidis [PC], distal cauda epididymidis [DC], and vas deferens [VD]) were assessed by in vitro fertilization (LVF) using limited sperm numbers, and by continuous evaluation of motility parameters during 5 hours of incubation in vitro with automated computer-aided sperm analysis (CASA). Spermatozoa from the PC region fertilized (68 +/- 6%) a significantly greater (P < or = 0.005) number of oocytes than those from the DC (44 + 5%) or VD (47 +/- 7%). For pooled samples from all three regions, the mean fertilization rate (51 +/- 14%) was less tan for spermatozoa from the PC (P < 0.05) but was not significantly different from spermatozoa from the DC or VD. For each time point and sample, 1,592 +/- 428 sperm tracks were analyzed. CASA was verified by comparison with manual still-frame analysis of video recordings, by repeated analysis of the same or different samples of spermatozoa, and by examination of computer tracks. The coefficients of variation for various motion parameters suggested that the CASA obtained a high degree of precision. There were no significant differences in motility parameters for spermatozoa recovered from equivalent regions of the left or right tract or in motility parameters for spermatozoa from different regions of the tract immediately after recovery. However, during incubation in vitro, spermatozoa from the DC or VD regions exhibited a marked decline in straight-line velocity (VSL) compared with spermatozoa from the PC region. The reduction in VSL (combined values from right and left tract) for DC or VD spermatozoa compared with PC spermatozoa was significant at 2.5 hours of incubation (P < or = 0.05) and highly significant (P < or = 0.005) by the end of the incubation period. Differences in average path velocity (VAP) were also apparent after 4 hours (p < or = 0.05), but no significant differences were observed for measurements of curvilinear velocity (VCL) or lateral bead displacement (ALH). Overall, the decline in VSL over 5 hours was highly correlated (P < or = 0.001) with the outcome of fertilization in vitro. In contrast, initial VSL and changes in VCL of spermatozoa were not correlated with fertilization rate. These results indicate that the in vitro fertilizing capacity of rat spermatozoa is correlated with 1) the decline in straight-line velocity (VSL) as measured by repeated CASA during incubation in vitro and 2) with the site of recovery of mature rat spermatozoa from the distal excurrent duct. It is suggested that the deterioration of the quality of rat spermatozoa in the distal epididymidis and vas deferens during storage may occur sooner than previously realized, and therefore care must be taken when recovering samples for fertility assessment. In keeping with findings in other species, immediate "snapshot" analysis of rat motility was a poor predictor of sperm fertility. In contrast, continuous CASA provided significant information for determining sperm fertilizing capacity and will be a useful technique for reproductive toxicology.