Sperm volumetric dynamics during in vitro capacitation process in bovine spermatozoa

The morphology, morphometry and functionality of fresh and cryopreserved wisent (Bison bonasus) epididymal spermatozoa

Epididymal spermatozoa obtained post mortem are considered a valuable source of genetic material which is often irrevocably lost. This makes these gametes constitute a key element in protection and restitution programs. The wisent (Bison bonasus, Linnaeus 1758) is a species that survived in zoos after extinction from its natural habitat. This resulted in a narrowing of the genetic pool of the whole population, which is at present derived from only 12 ancestors. Currently, wisent protection programs are aimed at preserving the genetic diversity by establishing a germplasm bank. The objective of this study was to comprehensively characterize the morphology, morphometry and functionality of wisent epididymal spermatozoa and evaluate the effectiveness of their cryopreservation in extender based on Tris buffer and chicken egg yolk. The median total number of spermatozoa obtained from one individual was 1985.0 × 106 (62.5 × 106-7452.0 × 106). These gametes were characterized by median: 40.0% (0.5-70.0%) subjective motility, 69.8% (32.5-90.0%) viability and 54.3% (10.5-83.3%) normal morphology. The sperm head had a median size of 5.0 μm (3.5-6.7 μm) width, 8.5 μm (6.4-11.3 μm) length and 36.9 μm2 (23.7-48.6 μm2) surface area. The viable population of the obtained gametes was characterized by median values 53.2% (4.5-80.3%) of intact sperm membrane, 50.8 (26.0-76.6%) of intact acrosome, 0.4% (0-98.7%) of fragmented chromatin, 5.9% (0.0-88.8%) of cells with high mitochondrial potential and 42.1% (8.3-63.7%) without lipid peroxidation. The viable population of the frozen/thawed gametes was characterized by median values: 18.4% (2.4-57.9%) of intact sperm membrane, 35.1 (11.9-56.7%) of intact acrosome, 0.07% (0-89.2%) of fragmented chromatin, 12.8% (0.0-49.7%) of cells with high mitochondrial potential and 16.3% (2.2-53.6%) without lipid peroxidation. Due to the material originating from a relatively large number of wild individuals, the research presented here contributed to the description of certain species standards for the assessment of wisent epididymal spermatozoa. The presented effect of cryopreservation on these gametes justifies the use of an extender based on Tris buffer with the addition of chicken egg yolk. The obtained effects are satisfactory from the point of view of preserving valuable genetic material and their use in ART.

Comparison of the structure of chinchilla sperm isolated from semen and from the tail of the epididymis

Sperm cells isolated from the tail of the epididymis and from the semen of the same individuals were analysed. The use of silver nitrate to stain sperm cells isolated from the tail of the epididymis made it possible to identify structures that were not visible in the sperm from semen. Silver nitrate very clearly distinguished the acrosomal and distal parts of the sperm head. Following silver nitrate staining, the sperm isolated from the tail of the epididymis were characterized by dark 'collars' in the distal part of the head. These 'collars' are not visible in the sperm cells isolated from semen. The results of the study indicate differences in the dimensions of sperm isolated from the tail of the epididymis and sperm in semen. Sperm isolated from the tail of the epididymis had smaller heads, despite their longer length, and had longer midpieces and tails than ejaculate sperm. Silver nitrate staining is a simple and fast technique. Silver nitrate makes it possible to identify the acrosome and post-acrosomal region of the sperm head and to clearly identify the midpiece. Therefore, it can be successfully used to supplement routine techniques for evaluating sperm morphology or as an independent technique.

[Capacitation and acrosome reaction are associated with changes in sialic acid location and head morphometry in human sperm]

OBJECTIVE

Assess changes in sialic acid distribution during capacitation and acrosome reaction processes, and evaluate head sperm morphometrics modifications in these physiological conditions in human sperm.

MATERIAL AND METHOD

In this prospective study, we included 6 normozoospermics sperm samples. Sialic acid distribution was evaluated by Wheat germ agglutinin lectin in different physiological conditions: before, after capacitation and after acrosome reaction. Head shape and size of each stage were analyzed by means of geometric morphometric methods.

RESULTS

After capacitation, 73.07±21.43% of sperm showed sialic acid in acrosomal region, linked with an acrosome expansion and equatorial segment contraction. Otherwise, after acrosome reaction higher allometric effect between stages was recorded since sperm undergo further expansion of equatorial segment. Regarding Wheat germ agglutinin location, we found that sperm percentage significant decline in acrosomal fluorescence and an increase of equatorial band labeling.

CONCLUSIONS

Our findings demonstrate that modifications in Wheat germ agglutinin expression covariate with dramatic changes in sperm head morphometry, suggesting important implications in capacitation and acrosome reaction processes.

Current status and potential of morphometric sperm analysis

The spermatozoon is the most diverse cell type known and this diversity is considered to reflect differences in sperm function. How the diversity in sperm morphology arose during speciation and what role the different specializations play in sperm function, however, remain incompletely characterized. This work reviews the hypotheses proposed to explain sperm morphological evolution, with a focus on some aspects of sperm morphometric evaluation; the ability of morphometrics to predict sperm cryoresistance and male fertility is also discussed. For this, the evaluation of patterns of change of sperm head morphometry throughout a process, instead of the study of the morphometric characteristics of the sperm head at different stages, allows a better identification of the males with different sperm cryoconservation ability. These new approaches, together with more studies employing a greater number of individuals, are needed to obtain novel results concerning the role of sperm morphometry on sperm function. Future studies should aim at understanding the causes of sperm design diversity and the mechanisms that generate them, giving increased attention to other sperm structures besides the sperm head. The implementation of scientific and technological advances could benefit the simultaneous examination of sperm phenotype and sperm function, demonstrating that sperm morphometry could be a useful tool for sperm assessment.

A novel approach to identifying physical markers of cryo-damage in bull spermatozoa

Cryopreservation is an efficient way to store spermatozoa and plays a critical role in the livestock industry as well as in clinical practice. During cryopreservation, cryo-stress causes substantial damage to spermatozoa. In present study, the effects of cryo-stress at various cryopreservation steps, such as dilution / cooling, adding cryoprtectant, and freezing were studied in spermatozoa collected from 9 individual bull testes. The motility (%), motion kinematics, capacitation status, mitochondrial activity, and viability of bovine spermatozoa at each step of the cryopreservation process were assessed using computer-assisted sperm analysis, Hoechst 33258/chlortetracycline fluorescence, rhodamine 123 staining, and hypo-osmotic swelling test, respectively. The results demonstrate that the cryopreservation steps reduced motility (%), rapid speed (%), and mitochondrial activity, whereas medium/slow speed (%), and the acrosome reaction were increased (P < 0.05). Differences (Δ) of the acrosome reaction were higher in dilution/cooling step (P < 0.05), whereas differences (Δ) of motility, rapid speed, and non-progressive motility were higher in cryoprotectant and freezing as compared to dilution/cooling (P < 0.05). On the other hand, differences (Δ) of mitochondrial activity, viability, and progressive motility were higher in freezing step (P < 0.05) while the difference (Δ) of the acrosome reaction was higher in dilution/cooling (P < 0.05). Based on these results, we propose that freezing / thawing steps are the most critical in cryopreservation and may provide a logical ground of understanding on the cryo-damage. Moreover, these sperm parameters might be used as physical markers of sperm cryo-damage.