Proteomic Investigation of Ram Spermatozoa and the Proteins Conferred by Seminal Plasma

Sperm
proteomes have emerged for several species; however, the
extent of species similarity is unknown. Sheep are an important agricultural
species for which a comprehensive sperm proteome has not been produced.
In addition, potential proteomic factors from seminal plasma that
may contribute to improved fertility after cervical insemination are
yet to be explored. Here we use liquid chromatography–tandem
mass spectrometry to investigate the proteome of ejaculated ram spermatozoa,
with quantitative comparison to epididymal spermatozoa. We also present
a comparison to published proteomes of five other species. We identified
685 proteins in ejaculated ram spermatozoa, with the most abundant
proteins involved in metabolic pathways. Only 5% of ram sperm proteins
were not detected in other species, which suggest highly conserved
structures and pathways. Of the proteins present in both epididymal
and ejaculated ram spermatozoa, 7% were more abundant in ejaculated
spermatozoa. Only two membrane-bound proteins were detected solely
in ejaculated sperm lysates: liver enriched gene 1 (LEG1/C6orf58)
and epidermal growth factor-like repeats and discoidin I-like domains
3 (EDIL3). This is the first evidence that despite its relatively
complex proteomic composition, seminal plasma exposure leads to few
novel proteins binding tightly to the ram sperm plasma membrane.