Live births from artificial insemination of microfluidic-sorted bovine spermatozoa characterized by trajectories correlated with fertility

Sperm selection methods in the 21st century

Natural sperm selection in humans is a rigorous process resulting in the highest quality sperm reaching, and having an opportunity to fertilize, the oocyte. Relative to other mammalian species, the human ejaculate consists of a heterogeneous pool of sperm, varying in characteristics such as shape, size, and motility. Semen preparation in assisted reproductive technologies (ART) has long been performed using either a simple swim-up method or density gradients. Both methodologies provide highly motile sperm populations; however neither replicates the complex selection processes seen in nature. A number of methods have now been developed to mimic some of the natural selection processes that exist in the female reproductive tract. These methods attempt to select a better individual, or population of, spermatozoa when compared to classical methods of preparation. Of the approaches already tested, platforms based upon sperm membrane markers, such as hyaluronan or annexin V, have been used to either select or deselect sperm with varied success. One technology that utilizes the size, motility, and other characteristics of sperm to improve both semen analysis and sperm selection is microfluidics. Here, we sought to review the efficacy of both available and emerging techniques that aim to improve the quality of the sperm pool available for use in ART.

Improvement in blastocyst quality by neurotensin signaling via its receptors in bovine spermatozoa during in vitro fertilization

Previously, we reported that neurotensin (NT), which is expressed in the uterus and oviduct, enhanced bovine sperm capacitation and acrosome reactions. As NT mRNA expression in bovine oviducts increases dramatically in the follicular phase, we hypothesized that NT modulates fertilization and subsequent conception in cattle. The objective of this study was to evaluate the effect of NT on embryo development and blastocyst quality. The rate of embryo cleavage was significantly increased by the addition of NT to the fertilization medium. Furthermore, the total number of cells and numbers of cells in the inner cell mass of blastocysts were significantly increased by NT during in vitro fertilization (IVF). These results suggested that NT enhanced the efficiency of early bovine embryo development and blastocyst quality. The expression of NT receptors (NTRs) in sperm, testes, oocytes, and cumulus cells was evaluated to determine whether NT acted via NTRs in sperm alone or in both male and female reproductive cells during IVF. Immunocytochemistry and reverse transcription polymerase chain reaction revealed that NTR1 and NTR2 were expressed in sperm and testes, but not in oocytes and cumulus cells. We propose that NT selectively acts upon sperm via NTR1 and NTR2 during IVF to improve the cleavage rate and quality of blastocysts, which are important determinants of sperm quality for successful conception. This research supports our hypothesis that NT acts as a key modulator of fertilization and conception in cattle. Further studies are necessary to apply our findings to the industrial framework of bovine reproduction.

Reconsideration of the evaluation criteria for bull ejaculated sperm motility in the context of rotation

Progressive movement of spermatozoa has conventionally been regarded as a good indicator of motility. However, bull spermatozoa exhibit two types of progressive movement: progressive/planar movement without rotation and progressive/helical movement with rotation. The aim of this study was to reconsider the evaluation criteria of bull ejaculated sperm motility in the context of rotation. Here, we compared the movement patterns of ejaculated spermatozoa with relatively high and low protein kinase A (PKA)-mediated signaling activities, because sperm motility is positively regulated by PKA-mediated signaling activities. We prepared sperm samples with high and low PKA-mediated signaling activities by suspending spermatozoa in media containing either the stimulator (NaHCO₃) or inhibitor (KH-7) of adenylyl cyclase 10, and we then investigated movement patterns and relative velocities using a microscopic high-speed camera and recording system. In the control medium without NaHCO₃ and KH-7, most spermatozoa exhibited round/planar movement without rotation and asymmetrical bends in the principal pieces. NaHCO₃ significantly promoted changes in movement patterns from round/planar movement to progressive/planar movement (without rotation) as well as symmetrization of flagellar bends and increased relative velocities. KH-7 significantly increased spermatozoa exhibiting progressive/helical movement (with rotation), decreased relative velocities, and symmetrized flagellar bends with a reduction in their size. These indicate that progressive/planar movement (without rotation) and fast movement characterize the movement patterns of bull ejaculated spermatozoa with high PKA-mediated signaling activities. A sign of reduced PKA-mediated signaling activity is not only slow movement but also helical movement (with rotation). Thus, it is beneficial to add a new parameter of “rotation” to the evaluation criteria of bull ejaculated sperm motility.