Comparative analysis reveals loss of the appetite-regulating peptide hormone ghrelin in falcons

A first glimpse into circulating ghrelin patterns of thin-billed prion chicks (Pachyptila belcheri)

The peptide hormone ghrelin, also known as "hunger hormone", is primarily secreted by the stomach and plays a key role in the regulation of vertebrate appetite and energy balance. While the hunger hormone and its functions have been extensively researched in mammalian species, its physiological roles have received less attention in birds and knowledge on the ghrelin system is especially poor in wild avian species. In contrast to mammals, ghrelin acts as an anorexigenic signal in birds and suppresses food intake. In this study, we focussed on the altricial chicks of thin-billed prions (Pachyptila belcheri) which are subjected to irregular, up to 8 day-long fasts, while waiting for their parents to return from feeding trips. We show that thin-billed prion chicks, which received a meal in the night prior to sampling, had higher circulating ghrelin levels than fasting conspecifics. Ghrelin levels did not correlate with chick body condition, meal size, or the length of a fast. Our study adds to past literature supporting an anorexigenic effect of avian ghrelin and is among the first to describe ghrelin profiles in seabirds, thereby significantly contributing to the scarce literature on ghrelin in wild avian species.

The unexpected loss of the 'hunger hormone' ghrelin in true passerines: a game changer in migration physiology

Migratory birds must accumulate large amounts of fat prior to migration to sustain long flights. In passerines, the small body size limits the amount of energy stores that can be transported, and therefore birds undergo cycles of extreme fattening and rapid exhaustion of reserves. Research on these physiological adaptations was rattled by the discovery that birds have lost the main vertebrate regulator of fat deposition, leptin. Recent studies have thus focused on ghrelin, known as 'hunger hormone', a peptide secreted by the gastrointestinal tract to regulate, e.g. food intake and body mass in vertebrates. Studies on domestic species showed that, in birds, ghrelin has effects opposite to those described in mammals such as inhibiting instead of promoting food intake. Furthermore, recent studies have shown that ghrelin administration influences migratory behaviour in passerine birds. Using comparative genomics and immunoaffinity chromatography, we show that ghrelin has been lost in Eupasseres after the basic split from Acanthisitti about 50 Ma. We found that the ghrelin receptor is still conserved in passerines. The maintenance of a functional receptor system suggests that in Eupasserines, another ligand has replaced ghrelin, perhaps to bypass the feedback system that would hinder the large pre-migratory accumulation of subcutaneous fat.

Rye-grass-derived probiotics alleviate heat stress effects on broiler growth, health, and gut microbiota

The primary aim of this study was to assess the impact of liquid (S-LAB) and lyophilized (L-LAB) probiotics sourced from Rye-Grass Lactic Acid Bacteria on broilers experiencing heat stress. The study involved 240 broiler chicks divided into six groups. These groups included a negative control (Control) with broilers raised at a normal temperature (24 °C) on a basal diet, and positive control groups (S-LAB and L-LAB) with broilers under normal temperature receiving a lactic acid bacteria supplement (0.5 mL/L) from rye-grass in their drinking water. The heat stress group (HS) comprised broilers exposed to cyclic heat stress (5-7 h per day at 34-36 °C) on a basal diet, while the heat stress and probiotic groups (S-LAB/HS and L-LAB/HS) consisted of broilers under heat stress supplemented with the rye-grass-derived lactic acid bacteria. Results indicated that heat stress without supplementation (HS) led to reduced body weight gain, T3 levels, citrulline, and growth hormone levels, along with an increased feed conversion ratio, serum corticosterone, HSP70, ALT, AST, and leptin levels. Heat stress also negatively impacted cecal microbiota, decreasing lactic acid bacteria (LABC) while increasing E. coli and coliform bacteria (CBC) counts. Probiotic supplements (S-LAB/HS and L-LAB/HS) mitigated these effects by enhancing broilers' resilience to heat stress. In conclusion, rye grass-derived S-LAB and L-LAB probiotics can effectively support broiler chickens under heat stress, promoting growth, liver function, hormonal balance, gut health, and cecal microbiome ecology. These benefits are likely mediated through improved gut health.

Regulating appetite in broilers for improving body and muscle development - A review

Appetite is the desire for feed and water and the voluntary intake of feed and is an important regulator of livestock productivity and animal health. Economic traits such as growth rate and muscle development (meat deposition) in broilers are directly correlated to appetite. Factors that may influence appetite include environmental factors, such as stress and temperature variation, and animal‐specific factors, such as learning period, eating capacity and preferences. Feed preferences have been reported to be determined in early life, and this period is important in broilers due to their fast growth and relatively short growth trajectories. This may be of importance when contemplating the use of more circular and sustainable feeds and the optimization of appetite for these feeds. The objective of this review was to review the biological mechanisms underlying appetite using data from human, animal and bird models and to consider the option for modulating appetite particularly as it relates to broiler chickens.

On the Molecular Evolution of Leptin, Leptin Receptor, and Endospanin

Over a decade passed between Friedman's discovery of the mammalian leptin gene (1) and its cloning in fish (2) and amphibians (3). Since 2005, the concept of gene synteny conservation (vs. gene sequence homology) was instrumental in identifying leptin genes in dozens of species, and we now have leptin genes from all major classes of vertebrates. This database of LEP (leptin), LEPR (leptin receptor), and LEPROT (endospanin) genes has allowed protein structure modeling, stoichiometry predictions, and even functional predictions of leptin function for most vertebrate classes. Here, we apply functional genomics to model hundreds of LEP, LEPR, and LEPROT proteins from both vertebrates and invertebrates. We identify conserved structural motifs in each of the three leptin signaling proteins and demonstrate Drosophila Dome protein's conservation with vertebrate leptin receptors. We model endospanin structure for the first time and identify endospanin paralogs in invertebrate genomes. Finally, we argue that leptin is not an adipostat in fishes and discuss emerging knockout models in fishes.

Multi-species sequence comparison reveals conservation of ghrelin gene-derived splice variants encoding a truncated ghrelin peptide

The peptide hormone ghrelin is a potent orexigen produced predominantly in the stomach. It has a number of other biological actions, including roles in appetite stimulation, energy balance, the stimulation of growth hormone release and the regulation of cell proliferation. Recently, several ghrelin gene splice variants have been described. Here, we attempted to identify conserved alternative splicing of the ghrelin gene by cross-species sequence comparisons. We identified a novel human exon 2-deleted variant and provide preliminary evidence that this splice variant and in1-ghrelin encode a C-terminally truncated form of the ghrelin peptide, termed minighrelin. These variants are expressed in humans and mice, demonstrating conservation of alternative splicing spanning 90 million years. Minighrelin appears to have similar actions to full-length ghrelin, as treatment with exogenous minighrelin peptide stimulates appetite and feeding in mice. Forced expression of the exon 2-deleted preproghrelin variant mirrors the effect of the canonical preproghrelin, stimulating cell proliferation and migration in the PC3 prostate cancer cell line. This is the first study to characterise an exon 2-deleted preproghrelin variant and to demonstrate sequence conservation of ghrelin gene-derived splice variants that encode a truncated ghrelin peptide. This adds further impetus for studies into the alternative splicing of the ghrelin gene and the function of novel ghrelin peptides in vertebrates.