Trypsin and Chymotrypsin are Involved in the Progesterone-Induced Acrosome Reaction in Canine Spermatozoa

Mating Stimulates the Immune Response and Sperm Storage-Related Genes Expression in Spermathecae of Bumblebee (Bombus terrestris) Queen

Bumblebee queens have remarkable spermathecae that store sperm for year-round reproduction. The spermathecal gland is regarded as a secretory organ that could benefit sperm storage. Queen mating provokes substantial physiological, behavioral, and gene expression changes. Here, the transcriptomes of spermathecae were compared between virgins and mated queens of the bumblebee, Bombus terrestris L., at 24 h post mating. Differentially expressed genes were further validated by real time quantitative PCR and immunofluorescence assay. In total, the expression of 11, 069 and 10, 862 genes were identified in virgins and mated queens, respectively. We identified that 176 differentially expressed genes between virgin and mated queen spermathecae: 110 (62.5%) genes were upregulated, and 66 (37.5%) genes were downregulated in mated queens. Most of the differentially expressed genes validated by RT-qPCR were concentrated on immune response [i.e., leucine-rich repeat-containing protein 70 (35.8-fold), phenoloxidase 2 (41.9-fold), and defensin (4.9-fold)] and sperm storage [i.e., chymotrypsin inhibitor (6.2-fold), trehalose transporter Tret1 (1.7-, 1.9-, 2.4-, and 2.4-fold), and heterogeneous nuclear ribonucleoprotein A3 (1.2-, and 2.6-fold)] functions in the spermathecae of mated queens. Procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1 (PLOD1) was hypothesized to promote the mating behavior according to RT-qPCR and immunofluorescence assay. The expression levels of most upregulated immune genes were decreased significantly at 3 days post mating. In conclusion, the external sperm transfer into spermathecae led to the significantly upregulated immune response genes in bumblebees. These gene expression differences in queen spermathecae contribute to understanding the bumblebee post mating regulatory network.

Kisspeptin Receptor on the Sperm Surface Reflects Epididymal Maturation in the Dog

Alongside the well-known central modulatory role, the Kisspeptin system, comprising Kiss1, its cleavage products (Kisspeptins), and Kisspeptin receptor (Kiss1R), was found to regulate gonadal functions in vertebrates; however, its functional role in the male gamete and its localization during maturation have been poorly understood. The present study analyzed Kisspeptin system in dog testis and spermatozoa recovered from different segments of the epididymis, with focus on Kiss1R on sperm surface alongside the maturation during epididymal transit, demonstrated by modification in sperm kinetic, morphology, and protamination. The proteins Kiss1 and Kiss1R were detected in dog testis. The receptor Kiss1R only was detected in total protein extracts from epididymis spermatozoa, whereas dot blot revealed Kiss1 immunoreactivity in the epidydimal fluid. An increase of the Kiss1R protein on sperm surface along the length of the epididymis, with spermatozoa in the tail showing plasma membrane integrity and Kiss1R protein (p < 0.05 vs. epididymis head and body) was observed by flow cytometry and further confirmed by epifluorescence microscopy and Western blot carried on sperm membrane preparations. In parallel, during the transit in the epididymis spermatozoa significantly modified their ability to move and the pattern of motility; a progressive increase in protaminization also occurred. In conclusion, Kisspeptin system was detected in dog testis and spermatozoa. Kiss1R trafficking toward plasma membrane along the length of the epididymis and Kiss1 in epididymal fluid suggested a new functional role of the Kisspeptin system in sperm maturation and storage.

Investigating media that support red wolf (Canis rufus) sperm viability and capacitation in vitro

The red wolf is a critically endangered canid, with ~250 and ~20 individuals in the ex situ and reintroduced wild populations, respectively. Assisted reproductive technologies such as sperm cryopreservation and in vitro fertilization therefore represent critically-needed tools to manage these populations. However, the motility of post-thaw red wolf sperm rapidly declines during in vitro incubation, hindering the ability to develop these technologies. In this study, we evaluated the influence of several culture media (a modified canine capacitation medium (mCCM), a modified North Carolina State University-23 medium (mNCSU-23), a synthetic oviductal fluid (SOF), a fertilization Tyrode's medium base or Fert-TALP (FERT), and a TRIS-based buffer (TRIS)) on the survival and capacitation of red wolf sperm during extended (18 h) incubation at 38.5°C and 5% CO₂. Red wolf sperm motility averaged (±s.e.m.) 73.8 ± 7.1% at the time of collection, and was better maintained over 4 h incubation in mCCM (55.0 ± 9.8%) and mNCSU-23 (54.7 ± 10.4), compared to mSOF (43.8 ± 8.3%), FERT (30 ± 10.5), and TRIS (16.4 ± 4.1%) solutions. Patterns of tyrosine phosphorylation signal, as assessed via immunocytochemistry, indicated induction of capacitation between 2 and 4 h in vitro culture. Tyrosine phosphorylation signal was particularly robust in mCCM and mNCSU-23 incubated sperm, although significant acrosome exocytosis was not observed in response to progesterone supplementation after 3 h incubation in any of the media. In sum, results indicate mCCM and mNCSU-23 are promising base media for the in vitro incubation and capacitation of red wolf sperm, for assisted reproduction applications.

Lay summary

Development of assisted reproductive technologies such as in vitro fertilization and artificial insemination is of high importance to the genetic management of critically endangered species such as the red wolf (Canis rufus). However, these technologies require the ability to maintain sperm viability and function during extended incubation, which has not been successful for the red wolf thus far. In this study, various culture media developed for sperm/egg/embryo culture in large mammalian species were evaluated for their ability to maintain red wolf sperm motility under physiological incubation conditions. Media and conditions previously utilized for domestic dog sperm were found to best support sperm incubation and capacitation (process of becoming competent to fertilize an egg) in the red wolf, representing a key step for future development of assisted reproductive technologies for the species.

Progesterone, spermatozoa and reproduction: An updated review

The rapid effects of steroids on spermatozoa have been demonstrated for the first time more than three decades ago. Progesterone (P), which is present throughout the female genital tract with peaks of levels in the cumulus matrix surrounding the oocyte, has been shown to stimulate several sperm functions in vitro, including capacitation, hyperactivation, chemotaxis and acrosome reaction (AR). Besides an increase of intracellular calcium, P has been shown to activate other sperm signalling pathways including tyrosine phosphorylation of several sperm proteins. All these effects are mediated by extra-nuclear pathways likely involving interaction with molecules present on the sperm surface. In particular, the increase in intracellular calcium ([Ca²⁺]_i) in spermatozoa from human and several other mammalian species is mediated by the sperm specific calcium channel CatSper, whose expression and function are required for sperm hyperactive motility. P-mediated CatSper activation is indeed involved in promoting sperm hyperactivation, but the involvement of this channel in other P-stimulated sperm functions, such as AR and chemotaxis, is less clear and further studies are required to disclose all the involved pathways. In human spermatozoa, responsiveness to P in terms of [Ca²⁺]_i increase and AR is highly related to sperm fertilizing ability in vitro, suggesting that the steroid is a physiological inducer of AR during in vitro fertilization. In view of their physiological relevance, P-stimulated sperm functions are currently investigated to develop new tools to select highly performant spermatozoa for assisted reproduction.

Three low molecular weight cysteine proteinase inhibitors of human seminal fluid: purification and enzyme kinetic properties

The cystatins form a superfamily of structurally related proteins with highly conserved structural folds. They are all potent, reversible, competitive inhibitors of cysteine proteinases (CPs). Proteins from this group present differences in proteinase inhibition despite their high level of structural similarities. In this study, three cysteine proteinase inhibitors (CPIs) of low molecular weight were isolated from human seminal fluid (HSF) by affinity chromatography on carboxymethyl (CM)-papain-Sepharose column, purified using various chromatographic procedures and checked for purity on sodium-dodecyl PAGE (SDS-PAGE). Matrix-assisted laser desorption-ionization-time-of flight-mass spectrometry (MALDI-TOF-MS) identified these proteins as cystatin 9, cystatin SN, and SAP-1 (an N-terminal truncated form of cystatin S). All three CPIs suppressed the activity of papain potentially and showed remarkable heat stability. Interestingly SAP-1 also inhibits the activity of trypsin, chymotrypsin, pepsin, and PSA (prostate specific antigen) and acts as a cross-class protease inhibitor in in vitro studies. Using Surface Plasmon Resonance, we have also observed that SAP-1 shows a significant binding with all these proteases. These studies suggest that SAP-1 is a cross-class inhibitor that may regulate activity of various classes of proteases within the reproductive systems. To our knowledge, this is the first report about purification of CPIs from HSF; the identification of such proteins could provide better insights into the physiological processes and offer intimation for further research.