RNA-sequencing of endometrial explants

Seminal plasma (SP) has been shown to modulate the female reproductive
environment in mammalian species in which the ejaculate comes into direct
contact with the endometrium, such as mice, pigs and horses. In contrast,
cattle ejaculate in the vagina, and it is questionable whether the fluid
portion reaches the uterus. A recent study from our group reported that
mating to intact, but not vasectomised, bulls modifies the endometrium
transcriptome. However, it is not clear whether these changes are driven
by SP molecules that bind to sperm at the time of ejaculation or not.
Thus, the aim of the present study was to determine whether ejaculated
sperm, which are suspended in the secretions of the accessory sex glands
(AGs) at ejaculation, elicit a different endometrial transcriptomic
response than epididymal sperm, which have never been exposed to SP
factors of AG origin. To this end, endometrial explants collected from
heifers in oestrus were (co-)incubated alone (control), or with epididymal
or ejaculated sperm, following which RNA-sequencing analysis was
performed. Endometrial exposure to epididymal sperm resulted in 48
differentially expressed genes (DEGs) compared with control explants.
Strikingly, explants exposed to ejaculated sperm exhibited no DEGs
compared with control explants. However, incubation with ejaculated sperm
resulted in 80 DEGs in comparison with epididymal sperm, involved in
muscle contraction, extracellular matrix remodelling, and immune system
pathways, among others. These data indicate that ejaculated and epididymal
sperm induce a different response in the endometrium, likely due to the
acquisition of SP components at the time of ejaculation.