Functions of Two Distinct “Prolactin-Releasing Peptides” Evolved from a Common Ancestral Gene

Abstract

Prolactin-releasing peptide (PrRP) is one of the RF-amide peptides and was originally identified in the bovine hypothalamus as a stimulator of prolactin (PRL) release. Independently, another RF-amide peptide was found in Japanese crucian carp and named Carassius-RFa (C-RFa), which shows high homology to PrRP and stimulates PRL secretion in teleost fish. Therefore, C-RFa has been recognized as fish PrRP. However, recent work has revealed that PrRP and C-RFa in non-mammalian vertebrates are encoded by separate genes originated through duplication of an ancestral gene. Indeed, both PrRP and C-RFa are suggested to exist in teleost, amphibian, reptile, and avian species. Therefore, we propose that non-mammalian PrRP (C-RFa) be renamed PrRP2. Despite a common evolutionary origin, PrRP2 appears to be a physiological regulator of PRL, whereas this is not a consistent role for PrRP itself. Further work revealed that the biological functions of PrRP and PrRP2 are not limited solely to PRL release, because they are also neuromodulators of several hypothalamus–pituitary axes and are involved in some brain circuits related to the regulation of food intake, stress, and cardiovascular functions. However, these actions appear to be different among vertebrates. For example, central injection of PrRP inhibits feeding behavior in rodents and teleosts, while it stimulates it in chicks. Therefore, both PrRP and PrRP2 have acquired diverse actions through evolution. In this review, we integrate the burgeoning information of structures, expression profiles, and multiple biological actions of PrRP in higher vertebrates, as well as those of PrRP2 in non-mammals.

Neuropeptide Control of Feeding Behavior in Birds and Its Difference with Mammals

“…Wang et al (2012) identified new chicken PrRP and showed that there are two types of PrRP encoded by separate genes. They also demonstrated that the chicken PrRP we previously identified (Tachibana et al, 2011; Tachibana and Sakamoto, 2014) is an ortholog of C-RFa, and newly identified chicken PrRP is an ortholog of mammalian PrRP. These two types of PrRP are thought to be produced by whole genome duplication (Wang et al, 2012; Tachibana and Sakamoto, 2014).…”

“…They also demonstrated that the chicken PrRP we previously identified (Tachibana et al, 2011; Tachibana and Sakamoto, 2014) is an ortholog of C-RFa, and newly identified chicken PrRP is an ortholog of mammalian PrRP. These two types of PrRP are thought to be produced by whole genome duplication (Wang et al, 2012; Tachibana and Sakamoto, 2014). Since newly identified chicken PrRP also increases food intake in neonatal chicks when administered centrally (Tachibana and Sakamoto, 2014), the role of PrRPs on feeding behavior is expected to have changed during the evolution of vertebrates.…”

“…These two types of PrRP are thought to be produced by whole genome duplication (Wang et al, 2012; Tachibana and Sakamoto, 2014). Since newly identified chicken PrRP also increases food intake in neonatal chicks when administered centrally (Tachibana and Sakamoto, 2014), the role of PrRPs on feeding behavior is expected to have changed during the evolution of vertebrates.…”

Sex-biased transcriptomic response of the reproductive axis to stress

“…A gene more lowly expressed in response to stress, Pro melanin concentrating hormone ( PMCH ) (logFC 3.8, FDR 2.532022e-05), can inhibit stress-induced ACTH release, stimulate anxiety and sexual behavior, and antagonize the inhibitory effect of alpha melanotropin on exploration behavior [33–35]. C-RFamide protein , also known as prolactin releasing hormone 2 [36] was also more lowly expressed in response to stress and can play a role in the release of prolactin as well as several gonadotropes [37] (logFC 4.7, FDR 2.52e-05). No significantly enriched gene ontology terms were revealed for genes differentially expressed in the male hypothalamus in response to stress The full differential dataset for the stress response of the male hypothalamus is available at https://git.io/vD40k.…”

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

“…In line with this hypothesis, in the euryhaline fish mudskipper ( Periophthalmus modestus , Perciforme, gobidae), freshwater fish have lower food intake/growth rates than saltwater fish and higher brain and intestine PrRP mRNA expressions, suggesting that PrRP is involved in the regulation of feeding and energy homeostasis in this species (Sakamoto et al, 2002; Tachibana and Sakamoto, 2014). …”