Expression of β-NGF and high-affinity NGF receptor (TrKA) in llama (Lama glama) male reproductive tract and spermatozoa.

β-Nerve growth factor (β-NGF) is a seminal plasma element, responsible for inducing ovulation in camelids. The main organ of β-NGF production remains nondescript. The aims of this study were to (a) characterize gene expression and protein localization of β-NGF and its main receptor tyrosine kinase receptor A (TrKA) in the llama male reproductive tract, and (b) determine whether the seminal β-NGF interacts with ejaculated sperm by localizing β-NGF and TrKA in epididymal, ejaculated, and acrosome-reacted (AR) sperms and, additionally, by identifying β-NGF presence in sperm-adsorbed proteins (SAP). Both β-NGF and TrkA transcripts are widely expressed along the male reproductive tract, with a higher expression level of β-NGF at prostate (p < 0.05). β-NGF immunolabeling was only positive for prostate, whereas TrKA label was present in epithelial and muscular cells of testis, prostate, bulbourethral glands, and epididymis. Using an immunofluorescent technique, β-NGF was colocalized with TrKA in the middle piece of ejaculated and AR sperm. However, only TrKA was observed in epididymal sperm indicating that β-NGF could have a seminal origin. This was also confirmed by the identification of four β-NGF isoforms in SAP. This study extends the knowledge about the participation of β-NGF/TrkA in llama reproduction, providing evidence that may have roles in the regulation of sperm physiology.