Expanding Duplication of Free Fatty Acid Receptor-2 (GPR43) Genes in the Chicken Genome

The gut microbiota and its metabolite butyrate shape metabolism and antiviral immunity along the gut-lung axis in the chicken

The gut microbiota exerts profound influence on poultry immunity and metabolism through mechanisms that yet need to be elucidated. Here we used conventional and germ-free chickens to explore the influence of the gut microbiota on transcriptomic and metabolic signatures along the gut-lung axis in poultry. Our results demonstrated a differential regulation of certain metabolites and genes associated with innate immunity and metabolism in peripheral tissues of germ-free birds. Furthermore, we evidenced the gut microbiota's capacity to regulate mucosal immunity in the chicken lung during avian influenza virus infection. Finally, by fine-analysing the antiviral pathways triggered by the short-chain fatty acid (SCFA) butyrate in chicken respiratory epithelial cells, we found that it regulates interferon-stimulated genes (ISGs), notably OASL, via the transcription factor Sp1. These findings emphasize the pivotal role of the gut microbiota and its metabolites in shaping homeostasis and immunity in poultry, offering crucial insights into the mechanisms governing the communication between the gut and lungs in birds.

The paralogs' enigma of germ-cell specific genes dispensable for fertility: the case of 19 oogenesin genes†

Gene knockout experiments have shown that many genes are dispensable for a given biological function. In this review, we make an assessment of male and female germ cell-specific genes dispensable for the function of reproduction in mice, the inactivation of which does not affect fertility. In particular, we describe the deletion of a 1 Mb block containing nineteen paralogous genes of the oogenesin/Pramel family specifically expressed in female and/or male germ cells, which has no consequences in both sexes. We discuss this notion of dispensability and the experiments that need to be carried out to definitively conclude that a gene is dispensable for a function.

The Expression of Amino Acid and Fatty Acid Receptors Show an Age-Dependent Pattern Involving Oral Cavity, Jejunum and Lower Gut Sensing in Broiler Chickens

This work aimed to evaluate the gene expression of amino acids (AA) and fatty acids (FA) sensors in the gastrointestinal tract (GIT) of chickens at two different ages (7 and 26 days post-hatch). Sixteen broilers (Ross 308) were selected, and ten sections of the GIT, including upper (tongue base, upper palate, crop, proventriculus), middle (gizzard, duodenum, jejunum, ileum), and lower GIT section (cecum, colon) were collected for analysis. Relative gene expression of AA (T1R1, T1R3, mGluR1, mGluR4, CaSR, GPR139, GPRC6A, GPR92) and FA (FFAR2, FFAR3, FFAR4) sensors were assessed using qPCR. The statistical model included age, GIT section, and gene. In addition, the correlations between gene expressions were calculated. At day 7, a significantly (p = 0.004) higher expression of AA sensors in the oral cavity and FA sensors in the lower GIT section (i.e., cecum and colon) compared to the middle section was recorded. A higher expression of AA compared to FA sensors was detected at the upper GIT section in 7 (p < 0.001) and 26-day-old chickens (p = 0.026). Thus, at day 7, AA sensors were predominantly (p < 0.05) expressed in the upper GIT section (mainly oral cavity), while FA sensors were mainly expressed in the lower GIT section, at cecum (FFR2 and 4) or colon (FFAR3). These results may indicate that in early life, both ends of the GIT are fundamental for feed intake (oral cavity) and development of the microbiota (cecum and colon). In contrast, at 26 days of age, the results showed the emergence of both AA and FA sensors in the jejunum, presumably indicating the essential role of the jejunum in the digestion absorption of nutrients and the signaling to the brain (gut-brain axis) through the enteroendocrine system. Significant positive correlations were observed between T1R1 and T1R3 (r = 0.85, p < 0.001), CaSR and T1R1 (r = 0.78, p < 0.001), CaSR and T1R3 (r = 0.45, p < 0.050), and mGluR1 and FFAR3 (r = 0.46, p < 0.050). It is concluded that the gene expression is greater in the oral cavity for AA sensors and the lower gut for FA sensors. On day 26, the role of jejunum regarding nutrient sensing is highlighted.

The avian taste system

Taste or gustation is the sense evolving from the chemo-sensory system present in the oral cavity of avian species, which evolved to evaluate the nutritional value of foods by detecting relevant compounds including amino acids and peptides, carbohydrates, lipids, calcium, salts, and toxic or anti-nutritional compounds. In birds compared to mammals, due to the relatively low retention time of food in the oral cavity, the lack of taste papillae in the tongue, and an extremely limited secretion of saliva, the relevance of the avian taste system has been historically undermined. However, in recent years, novel data has emerged, facilitated partially by the advent of the genomic era, evidencing that the taste system is as crucial to avian species as is to mammals. Despite many similarities, there are also fundamental differences between avian and mammalian taste systems in terms of anatomy, distribution of taste buds, and the nature and molecular structure of taste receptors. Generally, birds have smaller oral cavities and a lower number of taste buds compared to mammals, and their distribution in the oral cavity appears to follow the swallowing pattern of foods. In addition, differences between bird species in the size, structure and distribution of taste buds seem to be associated with diet type and other ecological adaptations. Birds also seem to have a smaller repertoire of bitter taste receptors (T2Rs) and lack some taste receptors such as the T1R2 involved in sweet taste perception. This has opened new areas of research focusing on taste perception mechanisms independent of GPCR taste receptors and the discovery of evolutionary shifts in the molecular function of taste receptors adapting to ecological niches in birds. For example, recent discoveries have shown that the amino acid taste receptor dimer T1R1-T1R3 have mutated to sense simple sugars in almost half of the living bird species, or SGLT1 has been proposed as a part of a T1R2-independent sweet taste sensing in chicken. The aim of this review is to present the scientific data known to date related to the avian taste system across species and its impact on dietary choices including domestic and wild species.

Connecting gut microbiomes and short chain fatty acids with the serotonergic system and behavior in Gallus gallus and other avian species

The chicken gastrointestinal tract has a diverse microbial community. There is increasing evidence for how this gut microbiome affects specific molecular pathways and the overall physiology, nervous system and behavior of the chicken host organism due to a growing number of studies investigating conditions such as host diet, antibiotics, probiotics, and germ-free and germ-reduced models. Systems-level investigations have revealed a network of microbiome-related interactions between the gut and state of health and behavior in chickens and other animals. While some microbial symbionts are crucial for maintaining stability and normal host physiology, there can also be dysbiosis, disruptions to nutrient flow, and other outcomes of dysregulation and disease. Likewise, alteration of the gut microbiome is found for chickens exhibiting differences in feather pecking (FP) behavior and this alteration is suspected to be responsible for behavioral change. In chickens and other organisms, serotonin is a chief neuromodulator that links gut microbes to the host brain as microbes modulate the serotonin secreted by the host's own intestinal enterochromaffin cells which can stimulate the central nervous system via the vagus nerve. A substantial part of the serotonergic network is conserved across birds and mammals. Broader investigations of multiple species and subsequent cross-comparisons may help to explore general functionality of this ancient system and its increasingly apparent central role in the gut-brain axis of vertebrates. Dysfunctional behavioral phenotypes from the serotonergic system moreover occur in both birds and mammals with, for example, FP in chickens and depression in humans. Recent studies of the intestine as a major site of serotonin synthesis have been identifying routes by which gut microbial metabolites regulate the chicken serotonergic system. This review in particular highlights the influence of gut microbial metabolite short chain fatty acids (SCFAs) on the serotonergic system. The role of SCFAs in physiological and brain disorders may be considerable because of their ability to cross intestinal as well as the blood-brain barriers, leading to influences on the serotonergic system via binding to receptors and epigenetic modulations. Examinations of these mechanisms may translate into a more general understanding of serotonergic system development within chickens and other avians.

Uncovering the core principles of the gut-lung axis to enhance innate immunity in the chicken

Research in mammals has evidenced that proper colonization of the gut by a complex commensal microbial community, the gut microbiota (GM), is critical for animal health and wellbeing. It greatly contributes to the control of infectious processes through competition in the microbial environment while supporting proper immune system development and modulating defence mechanisms at distant organ sites such as the lung: a concept named ‘gut-lung axis’. While recent studies point to a role of the GM in boosting immunity and pathogen resilience also in poultry, the mechanisms underlying this role are largely unknown. In spite of this knowledge gap, GM modulation approaches are today considered as one of the most promising strategies to improve animal health and welfare in commercial poultry production, while coping with the societal demand for responsible, sustainable and profitable farming systems. The majority of pathogens causing economically important infectious diseases in poultry are targeting the respiratory and/or gastrointestinal tract. Therefore, a better understanding of the role of the GM in the development and function of the mucosal immune system is crucial for implementing measures to promote animal robustness in commercial poultry production. The importance of early gut colonization in the chicken has been overlooked or neglected in industrial poultry production systems, where chicks are hampered from acquiring a complex GM from the hen. Here we discuss the concept of strengthening mucosal immunity in the chicken through GM modulation approaches favouring immune system development and functioning along the gut-lung axis, which could be put into practice through improved farming systems, early-life GM transfer, feeding strategies and pre-/probiotics. We also provide original data from experiments with germ-free and conventional chickens demonstrating that the gut-lung axis appears to be functional in chickens. These key principles of mucosal immunity are likely to be relevant for a variety of avian diseases and are thus of far-reaching importance for the poultry sector worldwide.

Rifaximin Protects against Malathion-Induced Rat Testicular Toxicity: A Possible Clue on Modulating Gut Microbiome and Inhibition of Oxidative Stress by Mitophagy

Testicular dysfunction is caused by chronic exposure to environmental pollution, such as malathion, which causes oxidative stress, promoting cell damage. Autophagy is a key cellular process for eliminating malfunctioning organelles, such as the mitochondria (mitophagy), an eminent source of reactive oxygen species (ROS). Autophagy is crucial for protection against testicular damage. Rifaximin (RFX) is a non-absorbable antibiotic that can reshape the gut microbiome, making it effective in different gastrointestinal disorders. Interestingly, the gut microbiome produces short chain fatty acids (SCFAs) in the circulation, which act as signal molecules to regulate the autophagy. In this study, we investigated the regulatory effects of RFX on gut microbiota and its circulating metabolites SCFA and linked them with the autophagy in testicular tissues in response to malathion administration. Moreover, we divided the groups of rats that used malathion and RFX into a two-week group to investigate the mitophagy process and a four-week group to study mitochondriogenesis. The current study revealed that after two weeks of cotreatment with RFX, apoptosis was inhibited, oxidative stress was improved, and autophagy was induced. More specifically, PINK1 was overexpressed, identifying mitophagy activation. After four weeks of cotreatment with RFX, there was an increase in acetate and propionate-producing microflora, as well as the circulating levels of SCFAs. In accordance with this, the expression of PGC-1α, a downstream to SCFAs action on their receptors, was activated. PGC-1α is an upstream activator of mitophagy and mitochondriogenesis. In this sense, the protein expression of TFAM, which regulates the mitochondrial genome, was upregulated along with a significant decrease in apoptosis and oxidative stress. Conclusion: we found that RFX has a positive regulatory effect on mitophagy and mitochondria biogenesis, which could explain the novel role played by RFX in preventing the adverse effects of malathion on testicular tissue.

Expanding duplication of the testis PHD Finger Protein 7 (PHF7) gene in the chicken genome

Gene duplications increase genetic and phenotypic diversity and occur in complex genomic regions that are still difficult to sequence and assemble. PHD Finger Protein 7 (PHF7) acts during spermiogenesis for histone-to-histone protamine exchange and is a determinant of male fertility in Drosophila and the mouse. We aimed to explore and characterise in the chicken genome the expanding family of the numerous orthologues of the unique mouse Phf7 gene (highly expressed in the testis), observing the fact that this information is unclear and/or variable according to the versions of databases. We validated nine primer pairs by in silico PCR for their use in screening the chicken bacterial artificial chromosome (BAC) library to produce BAC-derived probes to detect and localise PHF7-like loci by fluorescence in situ hybridisation (FISH). We selected nine BAC that highlighted nine chromosomal regions for a total of 10 distinct PHF7-like loci on five Gallus gallus chromosomes: Chr1 (three loci), Chr2 (two loci), Chr12 (one locus), Chr19 (one locus) and ChrZ (three loci). We sequenced the corresponding BAC by using high-performance PacBio technology. After assembly, we performed annotation with the FGENESH program: there were a total of 116 peptides, including 39 PHF7-like proteins identified by BLASTP. These proteins share a common exon-intron core structure of 8-11 exons. Phylogeny revealed that the duplications occurred first between chromosomal regions and then inside each region. There are other duplicated genes in the identified BAC sequences, suggesting that these genomic regions exhibit a high rate of tandem duplication. We showed that the PHF7 gene, which is highly expressed in the rooster testis, is a highly duplicated gene family in the chicken genome, and this phenomenon probably concerns other bird species.

Acetate promotes lipogenesis in adipocytes but not in hepatocytes of chickens

1.The role of acetate in lipogenesis of chickens remains largely unknown. This trial investigated the effect of sodium acetate (SA) on chicken fat metabolism via in vivo and in vitro experiments.2.The results indicated that supplementation of SA (1.0 g/kg feed) showed marginal to moderate stimulation on the area of the abdominal fat cells and triglyceride (TG) content in liver and adipose tissues. It increased the transcription of some genes involved in fat synthesis and deposition, but did not affect free fatty acid receptor 2 (FFAR2) expression in either liver or abdominal fat.3. In cultured hepatocytes treated with 0.01 mM to 5 mM SA, although mRNA levels of ACC1, PPAR, SREBP-1 c, and FFAR2 were upregulated with SA at certain concentrations, TG content and protein expression of lipogenic genes and FFAR2 were not altered at any dosages. In adipogenic differentiation of preadipocytes, high concentrations of SA (5 mM) exhibited significant increments in TG content and accumulated fat droplets, associated with stimulated transcription of FAS, LPL, AD, FABP4, and FFAR2, as well as elevated protein expression of FABP4 and FFAR2.4. The results showed that adipocytes were more sensitive to acetate than hepatocytes in chickens. While acetate played a minor role in hepatic fat metabolism, it promoted lipogenesis in adipocytes via FFAR2 with the involvement of FAS, LPL, and FABP4.

The Impact of Hydrated Aluminosilicates Supplemented in Litter and Feed on Chicken Growth, Muscle Traits and Gene Expression in the Intestinal Mucosa

Simple Summary

Poultry meat production has many challenges; one of them is the optimized use of natural feed and litter additives. Aluminosilicates have many properties, stimulating both the health and growth of birds and influencing the hygienic status of production. The objectives of the study were to compare growth, meat quality traits and gene expression in the intestinal mucosa of chickens, where halloysite and zeolite were added to the feed and litter simultaneously. There was a similar growth performance in all tested groups. There was no negative impact on most of the meat characteristics, and a positive effect on the water-holding capacity of the breast muscles was observed. The immunostimulatory and immunoregulatory properties of natural minerals have been demonstrated. Therefore, their use in the production of broiler chickens can be recommended.

Abstract

The aim of the study was to compare the production, muscle traits and gene expression in the intestinal mucosa of chickens supplemented with aluminosilicates in feed and litter simultaneously. A total of 300 Ross 308 were maintained for 42 days. Group 1 was the control group. In group 2, 0.650 kg/m² of halloysite was added to the litter and 0.5–2% to the feed (halloysite and zeolite in a 1:1 ratio); in group 3, we added zeolite (0.650 kg/m²) to the litter and 0.5–2% to the feed. The production parameters, the slaughter yield and analyses of muscle quality were analyzed. There was a higher body weight, body weight gain and feed conversion ratio on day 18 and 33 in group 3, and a higher feed intake on day 19–33 in groups 2 and 3 than in 1. A lower water-holding capacity was found in the breasts of group 2 and in the legs of group 3 compared to group 1. The expression of genes related to the immune response, host defense and intestinal barrier and nutrient sensing in the intestinal tissue was analyzed. The results show a beneficial effect on the immune status of the host without an adverse effect on the expression of genes related to intestinal tightness or nutritional processes. Due to the growth, meat characteristics and the positive impact of immunostimulant and regulating properties, aluminosilicates can be suggested as a litter and feed additive in the rearing of chickens.

The gut–brain axis in vertebrates: implications for food intake regulation

The gut and brain are constantly communicating and influencing each other through neural, endocrine and immune signals in an interaction referred to as the gut–brain axis. Within this communication system, the gastrointestinal tract, including the gut microbiota, sends information on energy status to the brain, which, after integrating these and other inputs, transmits feedback to the gastrointestinal tract. This allows the regulation of food intake and other physiological processes occurring in the gastrointestinal tract, including motility, secretion, digestion and absorption. Although extensive literature is available on the mechanisms governing the communication between the gut and the brain in mammals, studies on this axis in other vertebrates are scarce and often limited to a single species, which may not be representative for obtaining conclusions for an entire group. This Review aims to compile the available information on the gut–brain axis in birds, reptiles, amphibians and fish, with a special focus on its involvement in food intake regulation and, to a lesser extent, in digestive processes. Additionally, we will identify gaps of knowledge that need to be filled in order to better understand the functioning and physiological significance of such an axis in non-mammalian vertebrates.

Degree of Saturation and Free Fatty Acid Content of Fats Determine Dietary Preferences in Laying Hens

Simple Summary

Understanding fat sensing in chickens has the potential to improve least cost feed formulation relevant to poultry feeds. Acid oils (soybean acid oil and palm fatty acid distillate) are economical and sustainable feedstuffs with similar fatty acid composition to crude oils (soybean oil and palm oil) but richer in free fatty acids. However, potential issues relevant to the palatability of these oils have been raised. Four experimental diets were offered in a series of double-choice tests to study the effect of free fatty acid content and the unsaturated:saturated ratio on dietary preferences in hens. Hens showed a feed preference for palm oil added diets over soybean oil diets, with palm oil and palm fatty acid distillate being equally preferred. However, the hens demonstrated a preference for soybean oil when offered in choice with soybean acid oil. In conclusion, free fatty acid content and saturation degree affected feed preferences in hens. The use of oils with greater preference values may give rise to greater feed palatability, enhancing feed intake at critical stages.

Abstract

Behavioural and genetic evidence shows that the taste system is intimately related to the sensing of nutrients with consequences for poultry nutrition practices. A better understanding of how chickens may sense fat could provide the background for selecting feedstuffs used in poultry feeds. Acid oils have the potential to be economical and sustainable feedstuffs. These fat by-products from the edible oil refining industry possess a similar fatty acid composition to the crude oils but are richer in free fatty acids (FFA). An experiment was conducted to study the effect of FFA content and the unsaturated:saturated ratio (U:S) on dietary preferences in hens. Four fat sources were added to a basal diet at an inclusion rate of 6%, determining the experimental diets: soybean oil (SO; high U:S, 5% FFA); soybean acid oil (SA; high U:S, 50% FFA); palm oil (PO; low U:S, 5% FFA); and palm fatty acid distillate (PFAD; low U:S, 50% FFA). The experimental diets were offered in a series of double-choice tests to forty-eight Lohmann Brown laying hens housed individually in cages. Each hen was offered the ten potential binary combinations of the four diets including each diet compared to itself (referred to as four control double-choices). Feed intake was measured for two hours twice a day after one hour of fasting. Consumption was analysed as a standard preference index (% of test diet intake in comparison with the total intake). Preference values were compared to the random choice value of 50% using the Student’s t-test. None of the four control comparisons differ significantly from 50% (p > 0.05), indicating that the changes in preference values observed in the other binary comparisons were related to the dietary changes associated to fat ingredients. Hens showed a feed preference for palm oil added diets over soybean oil diets (p < 0.05), with PO and PFAD being equally preferred (p < 0.05). However, in this trial the hens demonstrated a preference for SO (low %FFA) when offered in choice with SA (high %FFA) (p < 0.05). These results suggest that the degree of saturation plays an important role in dietary fat preferences: hens prefer predominantly saturated oils even when these are rich in FFA. Furthermore, when presented with a choice between predominantly unsaturated oils, hens prefer feed with a low %FFA. In conclusion, %FFA and the U:S ratio affected feed preferences in hens. The use of oils with greater preference values may give rise to greater feed palatability, enhancing feed intake at critical stages.

Development of a Coccidiosis Disease Challenge Model Using a Commercially Available Live Oocyst Vaccine

With growing cross-disciplinary collaboration among researchers, it is increasingly important to record detailed methodology to prevent the repetition of preliminary experiments. The purpose of this paper is to explain the development of a coccidiosis challenge model for the investigation of dietary interventions to coccidiosis in broiler chickens. The objectives are to select a dose of mixed species coccidial vaccine and evaluate the suitability (ability to produce a consistent, marked change) of selected response variables important to nutritional studies at different times postinfection (PI). Coccivac-B and Coccivac-B52 (Merck Animal Health) were evaluated as the source of coccidia in three trials. Trials 1 and 2 were randomized complete block designs with four doses (0, 10, 20, or 30 times (×) label dose) of Coccivac-B administered to 12 replicate cages of six birds by repeater pipette (Trial 1) or gavaging needle (Trial 2). Trial 3 used a completely randomized design with 0× or 30× label dose of Coccivac-B52 administered by gavaging needle to six replicate cages of six birds. Birds were gavaged at 15 days of age, and response criteria were evaluated 7 days PI in all trials and again at 10 days PI in Trials 1 and 2. All means are reported in order of increasing coccidia dose with significance accepted at P ≤ 0.05. Broiler performance was not affected by coccidia in Trials 1 or 3 but grew poorer with increasing dose from 0 to 7 days PI in Trial 2 (body weight gain, 465, 421, 388, 365 g; feed to gain, 1.37, 1.47, 1.52, 1.58). As coccidia dose increased, nitrogen corrected apparent metabolizable energy decreased (Trial 1, 3387, 3318, 3267, 3170 kcal kg^-1; Trial 2, 3358, 2535, 2422, 2309 kcal kg^-1; Trial 3, not measured), while relative weight, length, and content for intestinal sections increased (Trials 1through 3). Gross lesion (duodenum, jejunum/ileum, ceca) and oocyst count scores (jejunum/ileum, ceca) increased with dose; however, gross scoring often suggested infection in unchallenged birds, a finding unsupported by oocyst count scores. At 7 days PI there was no correlation between midgut gross lesion score and midgut oocyst count score (r = 0.06, P = 0.705), but cecal scores were weakly correlated (r = 0.55, P < 0.001). Administering coccidia via repeater pipette (Trial 1) resulted in respiratory distress in some birds, while use of the gavaging needle (Trials 2 and 3) successfully induced intestinal damage in chickens without resulting in coccidia related mortality. Thirty times the label dose at 7 days PI resulted in the greatest number of response variables that produced a consistent, marked change. Therefore, consideration should be given to these conditions when designing future coccidiosis challenge models using vaccines as a source of coccidia.

Molecular characterization of free fatty acid receptors FFAR2 and FFAR3 in the domestic cat

G protein‐coupled receptors 41 and 43 were identified and characterized as free fatty acid receptors (FFAR) 3 and 2, respectively. FFAR2 and FFAR3 mediate short‐chain fatty acids (SCFAs) as signalling molecules. The present study aimed to give molecular characterization of FFAR2 and FFAR3 in the domestic cat. High homology with that in other mammals was revealed by cDNA cloning of cat FFAR2 FFAR3. We analyzed the tissue distribution of cat FFAR2 and FFAR3 mRNA using quantitative polymerase chain reaction. The inhibition of intracellular cAMP concentrations was observed in cells transfected with cat FFAR2 or FFAR3 and treated with SCFAs. The activation of nuclear factor of activated T cells‐luciferase reporter was only observed in cat FFAR2 transfected cells but not in FFAR3. Split luciferase assay (NanoLuc Binary Technology; NanoBiT) for FFAR2 or FFAR3 and Arrestin‐3/β‐arrestin‐2 revealed acetate‐/propionate‐induced recruitment to cat FFAR2 or FFAR3 in CHO‐K1 cells. Our results indicate that FFAR2 and FFAR3 are functional receptor proteins that are expressed in cat tissues and show differential distribution patterns.

Free Fatty Acid Receptors 2 and 3 as Microbial Metabolite Sensors to Shape Host Health: Pharmacophysiological View

The role of the gut microbiome in human health is becoming apparent. The major functional impact of the gut microbiome is transmitted through the microbial metabolites that are produced in the gut and interact with host cells either in the local gut environment or are absorbed into circulation to impact distant cells/organs. Short-chain fatty acids (SCFAs) are the major microbial metabolites that are produced in the gut through the fermentation of non-digestible fibers. SCFAs are known to function through various mechanisms, however, their signaling through free fatty acid receptors 2 and 3 (FFAR2/3; type of G-coupled protein receptors) is a new therapeutic approach. FFAR2/3 are widely expressed in diverse cell types in human and mice, and function as sensors of SCFAs to change several physiological and cellular functions. FFAR2/3 modulate neurological signaling, energy metabolism, intestinal cellular homeostasis, immune response, and hormone synthesis. FFAR2/3 function through Gi and/or Gq signaling, that is mediated through specific structural features of SCFAs-FFAR2/3 bindings and modulating specific signaling pathway. In this review, we discuss the wide-spread expression and structural homologies between human and mice FFAR2/3, and their role in different human health conditions. This information can unlock opportunities to weigh the potential of FFAR2/3 as a drug target to prevent human diseases.

Immunomodulation of Avian Dendritic Cells under the Induction of Prebiotics

Simple Summary

Dendritic cells recognize pathogen-associated molecular patterns in chicken intestines and are part of the initial immune response. The immunoregulatory properties of prebiotics acting in several ways in poultry have been known for many years. According to their function, dendritic cells should play an indispensable role in the proven effects of prebiotics on the intestinal immune system, such as through activation of T and B cells and cytokine production. Currently, there are no studies concerning direct interactions in poultry between non-digestible feed components and dendritic cells. Whereas most in vitro experiments with chicken dendritic cells have studied their interactions with pathogens, in vitro studies are now needed to determine the impacts of prebiotics on the gastrointestinal dendritic cells themselves. The present lack of information in this area limits the development of effective feed additives for poultry production. The main purpose of this review is to explore ideas regarding potential mechanisms by which dendritic cells might harmonize the immune response after prebiotic supplementation and thereby provide a basis for future studies.

Abstract

Although the immunomodulatory properties of prebiotics were demonstrated many years ago in poultry, not all mechanisms of action are yet clear. Dendritic cells (DCs) are the main antigen-presenting cells orchestrating the immune response in the chicken gastrointestinal tract, and they are the first line of defense in the immune response. Despite the crucial role of DCs in prebiotic immunomodulatory properties, information is lacking about interaction between prebiotics and DCs in an avian model. Mannan-oligosaccharides, β-glucans, fructooligosaccharides, and chitosan-oligosaccharides are the main groups of prebiotics having immunomodulatory properties. Because pathogen-associated molecular patterns on these prebiotics are recognized by many receptors of DCs, prebiotics can mimic activation of DCs by pathogens. Short-chain fatty acids are products of prebiotic fermentation by microbiota, and their anti-inflammatory properties have also been demonstrated in DCs. This review summarizes current knowledge about avian DCs in the gastrointestinal tract, and for the first-time, their role in the immunomodulatory properties of prebiotics within an avian model.

Evaluation of Waste Mushroom Compost as a Feed Supplement and Its Effects on the Fat Metabolism and Antioxidant Capacity of Broilers

Simple Summary

Mushroom waste compost is the main byproduct when cultivating mushrooms. Due to its high mycelium content, mushroom waste compost may improve animal health by increasing antioxidant capacity. Furthermore, increasing evidence suggests that supplementing animal diets with fiber could improve body composition and health. The results showed that supplementation with mushroom waste compost accelerates adipolysis and enhances the antioxidant capacity of broilers. Among all treatment groups, broilers given dietary supplementation with 0.5% mushroom waste compost showed improved feed conversion rate and the highest adipose metabolism.

Abstract

Pennisetum purpureum Schum No. 2 waste mushroom compost (PWMC) is the main byproduct when cultivating Pleurotus eryngii. Due to the high mycelium levels in PWMC, it may have potential as a feed supplement for broilers. This study investigated the effects of PWMC supplementation on antioxidant capacity and adipose metabolism in broilers. In the study, 240 broilers were randomly allocated to one of four treatment groups: basal diet (control), 0.5%, 1%, or 2% PWMC supplementation. Each treatment group had 60 broilers, divided into three replicates. The results showed that supplementation with 0.5% PWMC decreased the feed conversion rate (FCR) from 1.36 to 1.28, compared to the control. Supplementation with 0.5% or 2% PWMC decreased glucose and triglyceride levels, compared to the control (p < 0.0001), the concentrations of adiponectin and oxytocin increased from 5948 to 5709, 11820, and 7938 ng/ mL; and 259 to 447, 873, and 963 pg/ mL, respectively. Toll-like receptor 4 was slightly increased in the 0.5% and 1% PWMC groups. Both interferon-γ (IFN-γ) and interleukin-1ß (IL-1ß) were significantly decreased, by about three to five times for IFN-γ (p < 0.0001) and 1.1 to 1.6 times for IL-1ß (p = 0.0002). All antioxidant-related mRNA, including nuclear factor erythroid 2–related factor 2 (Nrf-2) and superoxidase dismutase-1 (SOD-1), increased significantly following PWMC supplementation. Both claudin-1 and zonula occludens 1 increased, especially in the 2% PWMC group. Excitatory amino acid transporter 3 (EAAT3) significantly increased by about 5, 12, and 11 times in the 0.5%, 1%, and 2% PWMC groups. All adipolysis-related mRNA were induced in the PWMC treatment groups, further enhancing adipolysis. Overall, 0.5% PWMC supplementation was recommended due to its improving FCR, similar antioxidant capacity, and upregulated adipolysis.

An evolutionary approach to recover genes predominantly expressed in the testes of the zebrafish, chicken and mouse

Background

Previously, we have demonstrated that genes involved in ovarian function are highly conserved throughout evolution. In this study, we aimed to document the conservation of genes involved in spermatogenesis from flies to vertebrates and their expression profiles in vertebrates.

Results

We retrieved 379 Drosophila melanogaster genes that are functionally involved in male reproduction according to their mutant phenotypes and listed their vertebrate orthologs. 83% of the fly genes have at least one vertebrate ortholog for a total of 625 mouse orthologs. This conservation percentage is almost twice as high as the 42% rate for the whole fly genome and is similar to that previously found for genes preferentially expressed in ovaries. Of the 625 mouse orthologs, we selected 68 mouse genes of interest, 42 of which exhibited a predominant relative expression in testes and 26 were their paralogs. These 68 mouse genes exhibited 144 and 60 orthologs in chicken and zebrafish, respectively, gathered in 28 groups of paralogs. Almost two thirds of the chicken orthologs and half of the zebrafish orthologs exhibited a relative expression ≥50% in testis. Finally, our focus on functional in silico data demonstrated that most of these genes were involved in the germ cell process, primarily in structure elaboration/maintenance and in acid nucleic metabolism.

Conclusion

Our work confirms that the genes involved in germ cell development are highly conserved across evolution in vertebrates and invertebrates and display a high rate of conservation of preferential testicular expression among vertebrates. Among the genes highlighted in this study, three mouse genes (Lrrc46, Pabpc6 and Pkd2l1) have not previously been described in the testes, neither their zebrafish nor chicken orthologs. The phylogenetic approach developed in this study finally allows considering new testicular genes for further fundamental studies in vertebrates, including model species (mouse and zebrafish).

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1462-8) contains supplementary material, which is available to authorized users.

Nutrient sensing, taste and feed intake in avian species

The anatomical structure and function of beaks, bills and tongue together with the mechanics of deglutition in birds have contributed to the development of a taste system denuded of macrostructures visible to the human naked eye. Studies in chickens and other birds have revealed that the avian taste system consists of taste buds not clustered in papillae and located mainly (60 %) in the upper palate hidden in the crevasses of the salivary ducts. That explains the long delay in the understanding of the avian taste system. However, recent studies reported 767 taste buds in the oral cavity of the chicken. Chickens appear to have an acute sense of taste allowing for the discrimination of dietary amino acids, fatty acids, sugars, quinine, Ca and salt among others. However, chickens and other birds have small repertoires of bitter taste receptors (T2R) and are missing the T1R2 (related to sweet taste in mammals). Thus, T1R2-independent mechanisms of glucose sensing might be particularly relevant in chickens. The chicken umami receptor (T1R1/T1R3) responds to amino acids such as alanine and serine (known to stimulate the umami receptor in rodents and fish). Recently, the avian nutrient chemosensory system has been found in the gastrointestinal tract and hypothalamus related to the enteroendocrine system which mediates the gut-brain dialogue relevant to the control of feed intake. Overall, the understanding of the avian taste system provides novel and robust tools to improve avian nutrition.

Regulation of CD4+CD8-CD25+ and CD4+CD8+CD25+ T cells by gut microbiota in chicken

The gut microbiota in chicken has long been studied, mostly from the perspective of growth performance. However, there are some immunological studies regarding gut homeostasis in chicken. Although CD4⁺CD25⁺ T cells are reported to act as regulatory T cells (Tregs) in chicken, there have been no studies showing the relationship between gut microbiota and Tregs. Therefore, we established a model for 'antibiotics (ABX)-treated chickens' through administration of an antibiotic cocktail consisting of ampicillin, gentamycin, neomycin, metronidazole, and vancomycin in water for 7 days. CD4⁺CD8^-CD25⁺ and CD4⁺CD8⁺CD25⁺ T cells in cecal tonsils were significantly decreased in this model. Gram-positive bacteria, especially Clostridia, was responsible for the changes in CD4⁺CD8^-CD25⁺ or CD4⁺CD8⁺CD25⁺ T cells in cecal tonsils. Feeding ABX-treated chickens with acetate recovered CD4⁺CD8^-CD25⁺ and CD4⁺CD8⁺CD25⁺ T cells in cecal tonsils. GPR43, a receptor for acetate, was highly expressed in CD4⁺CD8^-CD25⁺ T cells. In conclusion, our study demonstrated that the gut microbiota can regulate the population of CD4⁺CD8^-CD25⁺ and CD4⁺CD8⁺CD25⁺ T cells, and that acetate is responsible for the induction of CD4⁺CD8^-CD25⁺ T cells in cecal tonsils via GPR43.

Nutrient-Sensing Biology in Mammals and Birds

Nutrient-sensing mechanisms have emerged as the fringe articulating nutritional needs with dietary choices. Carbohydrate, amino acid, fatty acid, mineral, and water-sensing receptors are highly conserved across mammals and birds, consisting of a repertoire of 22 genes known to date. In contrast, bitter receptors are highly divergent and have a high incidence of polymorphisms within and between mammals and birds and are involved in the adaptation of species to specific environments. In addition, the expression of nutrient-sensing genes outside the oral cavity seems to mediate the required decision-making dialogue between the gut and the brain by translating exogenous chemical stimuli into neuronal inputs, and vice versa, to translate the endogenous signals relevant to the nutritional status into specific appetites and the control of feed intake. The relevance of these sensors in nondigestive systems has uncovered fascinating potential as pharmacological targets relevant to respiratory and cardiovascular diseases.

Invited review: nutrient-sensing receptors for free fatty acids and hydroxycarboxylic acids in farm animals

Data on nutrient sensing by free fatty acid receptors (FFAR1, FFAR2, FFAR3, FFAR4) and hydroxycarboxylic acid receptors (HCAR1, HCAR2) are increasing for human or rodent models. Both receptor families link intestinal fermentation by the microbiota and energy metabolism with cellular responses. Therefore, this finding provides a link that is independent of the only function of the fermentation products as energy substrates. For example, these reactions are associated with insulin secretion, regulation of lipolysis, adipose tissue differentiation and innate immune responses. In farm animals, the available data on both receptor families from the intestine and other tissues increase. However, currently, the data are primarily linked with the distribution of receptor messenger RNAs (mRNAs) and more rarely with proteins. Functional data on the importance of these receptors in farm animal species is not abundant and is often associated with the immune system. In certain farm animal species, the receptors were cloned and ligand binding was characterised. In chicken, only one FFAR2 was recently identified using genome analysis, which is contradictory to a study using an FFAR1 small interfering RNA. The chicken FFAR2 is composed of more than 20 paralogs. No data on HCAR1 or HCAR2 exist in this species. Currently, in pigs, most available data are on the mRNA distribution within intestine. However, no FFAR1 expression has been shown in this organ to date. In addition to FFAR2, an orthologue (FFAR2-like) with the highest abundance in intestine has been reported. The data on HCAR1 and HCAR2 in pigs is scarce. In ruminants, most of the currently available information on receptor distribution is linked to mRNA data and shows the expression, for example, in mammary gland and adipose tissue. However, some protein data on FFAR2 and FFAR1 protein has been reported and functional data availability is slowly increasing. The receptor mRNAs of HCAR1 and HCAR2 are expressed in bovine. The HCAR2 protein has been demonstrated in certain tissues, such as liver and fat. Because of the physiological importance of both receptor families in human life science, more studies that analyse the physiological significance of both receptor families in animal science may be performed within the next several years.