FE-SEM Characterization of α-Mannose Density and Surface Mapping Changes in Human Sperm Head During In Vitro Capacitation

A comprehensive N-glycome map of porcine sperm membrane before and after capacitation

Mapping the N-glycome of porcine sperm before and after sperm capacitation is important for understanding the rearrangement of glycoconjugates during capacitation. In this work, we characterized the N-glycome on the membranes of 18 pairs of fresh porcine sperm before capacitation and porcine sperm after capacitation by MALDI-MS (Matrix-assisted laser desorption/ionization-mass spectrometry). A total of 377 N-glycans were detected and a comprehensive N-glycome map of porcine sperm membranes before and after capacitation was generated, which presents the largest N-glycome dataset of porcine sperm cell membranes. Statistical analysis revealed a significantly higher level of high mannose glycosylation and a significantly lower level of fucosylation, galactosylation, and α-2,6-NeuAc after capacitation, which is further verified by flow cytometry and lectin blotting. This research reveals new insights into the relationship between N-glycosylation variations and sperm capacitation, including the underlying mechanisms of the capacitation process.

The Role of Sperm Proteins IZUMO1 and TMEM95 in Mammalian Fertilization: A Systematic Review

Gamete membrane fusion is a critical cellular event in sexual reproduction. In addition, the generation of knockout models has provided a powerful tool for testing the functional relevance of proteins thought to be involved in mammalian fertilization, suggesting IZUMO1 and TMEM95 (transmembrane protein 95) as essential proteins. However, the molecular mechanisms underlying the process remain largely unknown. Therefore, the aim of this study was to summarize the current knowledge about IZUMO1 and TMEM95 during mammalian fertilization. Hence, three distinct databases were consulted—PubMed, Scopus and Web of Science—using single keywords. As a result, a total of 429 articles were identified. Based on both inclusion and exclusion criteria, the final number of articles included in this study was 103. The results showed that IZUMO1 is mostly studied in rodents whereas TMEM95 is studied primarily in bovines. Despite the research, the topological localization of IZUMO1 remains controversial. IZUMO1 may be involved in organizing or stabilizing a multiprotein complex essential for the membrane fusion in which TMEM95 could act as a fusogen due to its possible interaction with IZUMO1. Overall, the expression of these two proteins is not sufficient for sperm–oocyte fusion; therefore, other molecules must be involved in the membrane fusion process.

Immunofluorescence and High-Resolution Microscopy Reveal New Insights in Human Globozoospermia

Globozoospermia is a rare and severe type of teratozoospermia characterized by the presence of round-headed, acrosomeless spermatozoa with cytoskeleton defects. Current data support a negative relationship between globozoospermia and intracytoplasmic sperm injection (ICSI) outcomes, revealing the need to perform exhaustive studies on this type of sperm disorder. The aim of this study was to evaluate different structural, functional and molecular sperm biomarkers in total globozoospermia with proper embryo development after ICSI. The combination of field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) allowed us to identify and correlate eight morphological patterns with both types of microscopy. Additionally, results reported a high percentage of coiled forms, with cytoplasmic retentions around the head and midpiece. By fluorescent microscopy, we detected that most of the sperm showed tubulin in the terminal piece of the flagellum and less than 1% displayed tyrosine phosphorylation in the flagellum. Moreover, we did not detect chaperone Heat shock-related 70 kDa protein 2 (HSPA2) in 85% of the cells. Overall, these findings provide new insights into globozoospermia, which could have potential implications in improving sperm selection methods for assisted reproductive techniques.

Quantification and Topographical Distribution of Terminal and Linked Fucose Residues in Human Spermatozoa by Using Field Emission Scanning Electron Microscopy (FE-SEM)

The modification of sperm glycocalyx is an essential process during sperm capacitation. The presence and redistribution of terminal and linked fucose have been described during in vitro capacitation in humans. However, the influence of the capacitation time on the quantification and localization of terminal and linked fucose is still unknown. In this study, the quantitative and qualitative changes in fucosyl residues during different in vitro capacitation times (1 and 4 h), are simultaneously characterized by using Aleuria aurantia (AAA) lectin-gold labelling and high-resolution field emission scanning electron microscopy (FE-SEM) in human sperm. A significant decrease was found in the number of terminal fucose registered in the whole sperm head during the in vitro capacitation. Nevertheless, the quantification of fucose residues after 1 h of in vitro capacitation was very similar to those found after 4 h. Therefore, the changes observed in terminal and linked fucose during capacitation were not time-dependent. Furthermore, the comprehensive analysis of the topographic distribution showed the preferential fucosyl location in the acrosomal region and the presence of distinct clusters distributed over the head in all the studied conditions. Overall, these findings corroborate the validity of FE-SEM combined with gold labelling to register changes in surface molecules during in vitro sperm capacitation.

Arylsulfatase A Remodeling during Human Sperm In Vitro Capacitation Using Field Emission Scanning Electron Microscopy (FE-SEM)

Capacitation drives sperm biophysical and biochemical changes for sperm-oocyte interactions. It is a well-known fact that the molecular complex arylsulfatase A (ARSA), hyaluronidase sperm adhesion molecule 1 (SPAM1), and heat shock protein 2 (HSPA2) plays a significant role in sperm-zona pellucida (ZP) binding. However, the time-dependent capacitation effects on the sperm surface ARSA presence and specific topographic distributions remain to be elucidated. Here, we quantified the ARSA density and specific membrane domain locations before (US) and after in vitro capacitation (one and four hours; CS1-CS4) in human sperm using high-resolution field emission scanning electron microscopy (FE-SEM) and immunogold labeling. Our results showed a significant and progressive capacitation-mediated increase of labeled spermatozoa from the US (37%) to CS4 (100%) physiological conditions. In addition, surface mapping revealed a close relationship between the ARSA residues and their acrosomal repositioning. Compared with the ARSA surface heterogeneous distribution found in US, the CS1-4 conditions exhibited clustering on the peri-acrosomal region, showing that time-dependent capacitation also induced a ARSA residue dramatic translocation on sperm surfaces. Our findings provide novel insights into the molecular remodeling events preceding sperm-oocyte interactions.