Evaluation of protein phosphorylation in bull sperm during their maturation in the epididymis

Sperm collection and characteristics analysis of the critically endangered Chinese pangolin (Manis pentadactyla)

The Chinese pangolin (Manis pentadactyla) is a critically endangered species. However, there is a paucity of research on the male reproductive gamete biology of this species. The present study was the first to systematically analyse the sperm characterization of the Chinese pangolin, including semen collection, sperm morphometry and ultrastructure. The semen of five male Chinese pangolins was successfully collected using the electroejaculation method. CASA (computer-assisted sperm analysis) was used to assess semen quality and take images for sperm morphometric analysis. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for sperm ultrastructure observation. The results showed that the semen of the Chinese pangolin was yellow to pale yellow in colour, viscous, with a fishy odour, and a slightly alkaline pH of between 7.7 and 7.9. The head defects were the main sperm defects; there were 13 kinds of head defects counted in this study. The total sperm length, head length, head width and tail length were 67.62 ± 0.21 μm, 10.47 ± 0.06 μm, 1.33 ± 0.006 μm and 57.16 ± 0.20 μm, respectively. SEM observed that the spermatozoa had a rod-shaped head with a distinct apical ridge, which was different from most mammals and similar to that in avians and reptiles. Interestingly, TEM found that the acrosome membrane of the Chinese pangolin had a double membrane structure rather than a multiple bi-lamellar membrane structure as reported by the previous study. Collectively, this study contributes to the development of artificial breeding efforts and assisted reproductive techniques for the Chinese pangolin, as well as providing technical support for research on germplasm conservation of this species.

Quantitative phosphoproteomics explain cryopreservation-induced reductions in ram sperm motility

Sperm cryopreservation decreases motility, probably due to changes in protein phosphorylation. Our objective was to use quantitative phosphoproteomics for systematic comparative analyses of fresh versus frozen-thawed sperm to identify factors causing cryo-injury. Ejaculates were collected (artificial vagina) from six Dorper rams, pooled, extended, and frozen over liquid nitrogen. Overall, 915, 3382, and 6875 phosphorylated proteins, phosphorylated peptides, and phosphorylation sites, respectively, were identified. At least two modified sites were present in 57.94% of the 6875 phosphosites identified, of which AKAP4 protein contained up to 331 modified sites. There were 732 phosphorylated peptides significantly up-regulated and 909 significantly down-regulated in frozen-thawed versus fresh sperm. Moreover, the conserved motif [RxxS] was significantly down-regulated in frozen-thawed sperm. Phosphorylation of sperm-specific proteins, e.g., AKAP3/4, CABYR, FSIP2, GSK3A/B, GPI, and ODF1/2 make them potential biomarkers to assess the quality of frozen-thawed ram sperm. Furthermore, these differentially phosphorylated proteins and modification sites were implicated in cryopreservation-induced changes in sperm energy production, fiber sheath composition, and various biological processes. We concluded that abnormal protein phosphorylation modifications are key regulators of reduced sperm motility. These novel findings implicated specific protein phosphorylation modifications in sperm cryo-injury. SIGNIFICANCE: This study used phosphorylated TMT quantitative proteomics to explore regulation of epigenetic modifications in frozen-thawed ram sperm. This experiment demonstrated that ram sperm freezing affects phosphorylation site modifications of proteins, especially those related to functions such as sperm motility and energy production. Furthermore, it is important to link functions of phosphorylated proteins with changes in sperm quality after freezing and thawing, and to clarify intrinsic reasons for sperm quality changes, which is of great importance for elucidating mechanisms of sperm freezing damage. Based on these protein markers and combined with cryoprotectant design theory, it provides a theoretical basis and data reference to study sperm cryoprotectants.

Influence of the Season and Region Factor on Phosphoproteome of Stallion Epididymal Sperm

Epididymal maturation can be defined as a scope of changes occurring during epididymal transit that prepare spermatozoa to undergo capacitation. One of the most common post-translational modifications involved in the sperm maturation process and their ability to fertilise an oocyte is the phosphorylation of sperm proteins. The aim of this study was to compare tyrosine, serine, and threonine phosphorylation patterns of sperm proteins isolated from three subsequent segments of the stallion epididymis, during and out of the breeding season. Intensities of phosphorylation signals and phosphoproteins profiles varied in consecutive regions of the epididymis. However, significant differences in the phosphorylation status were demonstrated in case of endoplasmic reticulum chaperone BiP (75 and 32 kDa), protein disulfide-isomerase A3 (50 kDa), nesprin-1 (23 kDa), peroxiredoxin-5 (17 kDa), and protein bicaudal D homolog (15 kDa) for season x type of phosphorylated residues variables. Significant differences in the phosphorylation status were also demonstrated in case of endoplasmic reticulum chaperone BiP and albumin (61 kDa), protein disulfide-isomerase A3 (50 kDa), and protein bicaudal D homolog (15 kDa) for region x type of phosphorylated residues variables.

Prepubertal arsenic exposure alters phosphoproteins profile, quality, and fertility of epididymal spermatozoa in sexually mature rats

Arsenic intoxication affects male reproductive parameters of prepubertal rats. Besides, morphological and functional alterations in their testis and epididymis may remain after withdrawal of arsenic insult, causing potential impairment in male fertility during adulthood. In this study, we aimed at analyzing the effect of prepubertal arsenic exposure on the fecundity of epididymal sperm from sexually mature Wistar rats, assessing fertility indexes, sperm parameters, and sperm phosphoproteins content. Male pups on postnatal day (PND) 21 received filtered water (controls, n = 10) and 10 mg L^-1 arsenite (n = 10) daily for 30 days. From PND52 to PND81, rats from both groups received filtered water. During this period, the males mated with non-exposed females between PND72 and PND75. Our results showed that sexually mature rats presented low sperm production, epididymal sperm count, motility, and quality after prepubertal arsenic exposure. These findings possibly contributed to the low fertility potential and high preimplantation loss. Epididymal sperm proteome detected 268 proteins, which 170 were found in animals from both control and arsenic groups, 27 proteins were detected only in control animals and 71 proteins only in arsenic-exposed rats. In these animals, SPATA 18 and other five proteins were upregulated, whereas keratin type II cytoskeletal 1 was downregulated (q < 0.1). The results of KEGG pathway analysis demonstrated an enrichment of pathways related to dopaminergic response, adrenergic signaling, protein degradation, and oocyte meiosis in arsenic-exposed animals. Moreover, 26 proteins were identified by phosphoproteomic with different phosphorylation pattern in animals from both groups, but SPATA18 was phosphorylated only in arsenic-exposed animals. We concluded that prepubertal exposure to arsenic is deleterious to sperm quality and male fertility, altering the sperm phosphoproteins profile.

Changes in the Cellular Distribution of Tyrosine Phosphorylation and Its Relationship with the Acrosomal Exocytosis and Plasma Membrane Integrity during In Vitro Capacitation of Frozen/Thawed Bull Spermatozoa

During sperm capacitation, intracellular signaling leads to protein tyrosine phosphorylation (PTP) of multiple cellular structures. However, the connection of this molecular signaling to the physiology of capacitated spermatozoa is not completely understood. This is the case of the short lifespan of capacitated spermatozoa and their increased susceptibility to initiate acrosomal exocytosis (AE) during incubation. Herein, by employing frozen/thawed bull spermatozoa, we aimed to study the relationship between PTP with AE and with plasma membrane integrity (PMI) at the cellular level. For this, we employed double staining following immunofluorescence for PTP combined with fluorescence probes for the acrosome (PNA-FITC) and PMI (LIVE/DEAD Fixable Dead Cell Stain Kit). Our results revealed that the presence of PTP at sperm head was less abundant in the sperm fraction that triggered the AE after 3 h of incubation under capacitating conditions, or by its induction with calcium ionophore, compared to the unreacted fraction. Furthermore, PTP at the equatorial region of the head (PTP-EQ) was enriched in the fraction showing damaged membrane while induction of AE with calcium ionophore did not alter the PMI and its relation to PTP-EQ. These results suggest that spontaneous AE and induced AE trigger similar cellular events regarding PTP and the spermatozoa showing PTP-EQ are more prone to suffer plasma membrane damage.