Preliminary Evaluation of Seminal Plasma Proteins and Immunoreactivity of Nerve Growth Factor as Indicative of an Ovulation Inducing Factor in Odontocetes

Abstract

In the seminal plasma of terrestrial mammalian species known as induced (e.g., camels) and spontaneous (e.g., cattle) ovulators, an ovulation-inducing factor (OIF) with a protein structure similar to beta-nerve growth factor (β-NGF) has been identified. Detection of an OIF/NGF in the seminal plasma of cetaceans would have both basic and applied implications in reproductive biology and conservation management programs. A preliminary evaluation was conducted to characterize the distribution and abundance of seminal plasma proteins in aquarium-based belugas and a Pacific white-sided and bottlenose dolphin. Initially, SDS-PAGE was used with 50 µg of total protein for separation; thereafter, Western immunoblot was used with anti-NGF. In addition to odontocete seminal plasma, a purified fraction of llama seminal plasma (100 ng protein) and an extract of mouse brain (20 µg total protein) were included as positive controls for NGF. Within the two belugas, visual inspection of the protein bands indicated similar distribution and intensity. However, among the belugas and Pacific white-sided and bottlenose dolphins there was more diversity than similarity in the distribution and abundance of seminal plasma proteins. While immunoreactivity of NGF was distinctly evident in the llama and mouse positive controls, there was no visual reactivity in any of the odontocete samples. These preliminary results provide novel information indicating more homogeneity within and heterogeneity among seminal plasma proteins of ondentocetes. Although NGF was not immunologically detected, future studies are required to address the apparent limitations of immuno-detection of NGF, especially if the post-translational form of β-NGF is in low abundance in the seminal plasma of belugas and Pacific white-sided and bottlenose dolphins.