Bovine sperm-oviduct interactions are characterized by specific sperm behaviour, ultrastructure and tubal reactions which are impacted by sex sorting

Abstract

To date sperm-oviduct interactions have largely been investigated under in vitro conditions. Therefore we set out to characterize the behaviour of bovine spermatozoa within the sperm reservoir under near in vivo conditions and in real-time using a novel live cell imaging technology and a newly established fluorescent sperm binding assay. Sperm structure and tubal reactions after sperm binding were analysed using scanning and transmission electron microscopy and histochemistry. As a model to specify the impact of stress on sperm-oviduct interactions, frozen-thawed conventional and sex-sorted spermatozoa from the same bulls (n = 7) were co-incubated with oviducts obtained from cows immediately after slaughter. Our studies revealed that within the oviductal sperm reservoir agile (bound at a tangential angle of about 30°, actively beating undulating tail), lagging (bound at a lower angle, reduced tail movement), immotile (absence of tail movement) and hyperactivated (whip-like movement of tail) spermatozoa occur, the prevalence of which changes in a time-dependent pattern. After formation of the sperm reservoir, tubal ciliary beat frequency is significantly increased (p = 0.022) and the epithelial cells show increased activity of endoplasmic reticula. After sex sorting, spermatozoa occasionally display abnormal movement patterns characterized by a 360° rotating head and tail. Sperm binding in the oviduct is significantly reduced (p = 0.008) following sexing. Sex-sorted spermatozoa reveal deformations in the head, sharp bends in the tail and a significantly increased prevalence of damaged mitochondria (p < 0.001). Our results imply that the oviductal cells specifically react to the binding of spermatozoa, maintaining sperm survival within the tubal reservoir. The sex-sorting process, which is associated with mechanical, chemical and time stress, impacts sperm binding to the oviduct and mitochondrial integrity affecting sperm motility and function.

A Computational Study of Hydrodynamic Interactions Between Pairs of Sperm With Planar and Quasi-Planar Beat Forms

“…Likely, these signaling molecules will either act to break bonds of the cell body with the wall or bind to the flagellum and initiate a different beat form that will aid in generating increased force to break away from the wall [18,19]. There are many interesting and unanswered questions as to how sperm get to the walls, how long they stay at the walls, as well as how the sperm reservoir could act as a filter to sort out healthy sperm [20,21]. Investigations with microfluidic channels have revealed that sperm guidance can be achieved with surface topography and microchannels [22,23].…”

Sperm‐oviduct interactions: Key factors for sperm survival and maintenance of sperm fertilizing capacity

“…Importantly, sperm motility is preserved in the sperm reservoir and is sustained by the molecular interactions with the oviduct and secretions such as glycoproteins and acidic mucopolysaccharides, which are produced by the secretory cells of the tubal epithelium 16 . LCI revealed that 5%–15% of the sperm in the reservoir reveal hyperactivation.…”

“…LCI revealed that 5%–15% of the sperm in the reservoir reveal hyperactivation. They show an asymmetrical high amplitude and a whip‐like beating of the tail and a rotating head 16 . Hyperactivation is an important key behavior of sperm, which allows them to detach from the tubal epithelium and to penetrate the cumulus oophorus of the oocyte after ovulation 39,40 .…”

“…However, it is important that especially due to freezing and thawing, there is a percentage of sperm, which is immotile or dies already during the migration in the female genital tract. They are seen as floating immotile spermatozoa in the oviductal fluid 16 (Figure 1, upper circle).…”

Assessment of Sperm Binding Capacity in the Tubal Reservoir Using a Bovine Ex Vivo Oviduct Culture and Fluorescence Microscopy

“…Sperm binding assays often only measure binding capacity to a single glycoprotein or ligand and do not take the multi-molecular nature of sperm-oviduct interactions into account [27]. Monolayers of ciliated epithelial cells lack the 3D orientation of the oviductal folds [28], the response of secretory cells to sperm binding [29] and paracrine signaling between neighboring cells [30]. In a similar manner, spheroid explants do not accurately replicate the scaffolding anatomy of the oviduct [28].…”