Exploring the Neuropeptidome of the Hypothalamus and Pituitary Gland of PRE- and POST-Pubertal Brangus Heifers

Puberty is a complex physiological event as neuropeptides and neurotransmitters influence synthesis and tonic secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus and gonadotropins from the pituitary gland. Brahman-influenced (Bos indicus) cattle are at a disadvantage in production systems requiring early maturity because they achieve puberty at much older ages than Angus (Bos taurus) cattle. Objectives of this study were to characterize the peptidome of hypothalamic and pituitary gland in pre- (PRE) and post- (POST) pubertal Brangus heifers. Heifers were 3/8 Brahman x 5/8 Angus; puberty status was determined with serum progesterone concentrations and POST tissues were collected during luteal phase of the estrous cycle. Using nanoflow liquid chromatography and mass spectrometry qualitative analyses of undigested peptide extracts, 874 peptides were detected with >95% confidence. Of these, 70.1% were presumed degradation or protein turnover products. Thus, 240 neuropeptides ≤ 10 kDa in size were confirmed in the two tissues. The pituitary gland was a richer source of neuropeptides than the hypothalamus (150 vs. 138 neuropeptides, respectively). Pre-pubertal heifers expressed 28.5% more peptides in hypothalamus than POST, whereas in pituitary glands, POST heifers expressed 31.1% more peptides than PRE females. On average, 53.3 ± 11.2 peptides were co-expressed across tissues and pubertal states. Ninety-three of the 240 neuropeptides detected were products of the pro-opiomelanocortin (POMC) precursor. Understanding the transcriptome and proteome of reproductive tissues will aide development of genomic selection strategies for fertility traits in composite breeds of cattle.