Ian C. Dunn

The dynamics of chromosome evolution in birds and mammals.

Comparative mapping, which compares the location of homologous genes in different species, is a powerful tool for studying genome evolution. Comparative maps suggest that rates of chromosomal change in mammals can vary from one to ten rearrangements per million years. On the basis of these rates we would expect 84 to 600 conserved segments in a chicken comparison with human or mouse. Here we build comparative maps between these species and estimate that numbers of conserved segments are in the lower part of this range. We conclude that the organization of the human genome is closer to that of the chicken than the mouse and by adding comparative mapping results from a range of vertebrates, we identify three possible phases of chromosome evolution. The relative stability of genomes such as those of the chicken and human will enable the reconstruction of maps of ancestral vertebrates.

Gonadotrophin Inhibitory Hormone Depresses Gonadotrophin α and Follicle-Stimulating Hormone β Subunit Expression in the Pituitary of the Domestic Chicken

Studies performed in vitro suggest that a novel 12 amino acid RF amide peptide, isolated from the quail hypothalamus, is a gonadotrophin inhibitory hormone (GnIH). The aim of the present study was to investigate this hypothesis in the domestic chicken. Injections of GnIH into nest‐deprived incubating hens failed to depress the concentration of plasma luteinizing hormone (LH). Addition of GnIH to short‐term (120u2003min) cultures of diced pituitary glands from adult cockerels depressed follicle‐stimulating hormone (FSH) and LH release and depressed common α and FSHβ gonadotrophin subunit mRNAs, with no effect on LHβ subunit mRNA. Hypothalamic GnIH mRNA was higher in incubating (out‐of‐lay) than in laying hens, but there was no significant difference in the amount of hypothalamic GnIH mRNA in out‐of‐lay and laying broiler breeder hens at the end of a laying year. It is concluded that avian GnIH may play a role in controlling gonadotrophin synthesis and associated constitutive release in the domestic chicken.

Gallin; an antimicrobial peptide member of a new avian defensin family, the ovodefensins, has been subject to recent gene duplication

BackgroundEgg white must provide nutrients and protection to the developing avian embryo. One way in which this is achieved is an arsenal of antimicrobial proteins and peptides which are essentially extensions of the innate immune system. Gallin is a recently identified member of a family of peptides that are found in egg white. The function of this peptide family has not been identified and they are potentially antimicrobial.ResultsWe have confirmed that there are at least 3 forms of the gallin gene in the chicken genome in 3 separate lines of chicken, all the forms are expressed in the tubular cells of the magnum region of the oviduct, consistent with its presence in egg white. mRNA expression levels are in the order 10,000 times greater in the magnum than the shell gland. The conservation between the multiple forms of gallin in the chicken genome compared with the conservation between gallin and other avian gallin like peptides, suggests that the gene duplication has occurred relatively recently in the chicken lineage. The gallin peptide family contains a six cysteine motif (C-X5-C-X3-C-X11-C-X3-C-C) found in all defensins, and is most closely related to avian beta-defensins, although the cysteine spacing differs. Further support for the classification comes from the presence of a glycine at position 10 in the 41 amino acid peptide. Recombinant gallin inhibited the growth of Escherischia coli (E. coli) at a concentration of 0.25 μM confirming it as part of the antimicrobial innate immune system in avian species.ConclusionsThe relatively recent evolution of multiple forms of a member of a new defensin related group of peptides that we have termed ovodefensins, may be an adaptation to increase expression or the first steps in divergent evolution of the gene in chickens. The potent antimicrobial activity of the peptide against E. coli increases our understanding of the antimicrobial strategies of the avian innate immune system particularly those of the egg white and the evolution of the defensin family. The potential of this peptide and others in the family can now be investigated in a number of novel antimicrobial roles.

Heritability and genetic correlation of measurements derived from acoustic resonance frequency analysis; a novel method of determining eggshell quality in domestic hens.

1. Cracked eggshells result in economic loss and provide a route for pathogenic organisms to enter the egg. Genetic factors that contribute to shell strength are likely to decrease the risk that an egg will crack when subject to insult. 2. A novel measurement, the dynamic stiffness of the eggshell (K dyn) was examined to determine if it might be used in the genetic selection of hens with improved eggshell characteristics. The measurement is determined from acoustic resonance frequency analysis. 3. The estimates of heritability for the novel measurement of K dyn were moderately high and ranged from 0·33 to 0·53 depending on the model used for the estimation. 4. The estimates of genetic correlation of K dyn with eggshell breaking strength (0·49) and static stiffness (0·57) were positive and relatively large as expected. There was a small negative genetic correlation between K dyn and egg production from 26 to 50 weeks of age (−0·19) and a moderate one from 58 to 74 weeks of age (−0·36). 5. The moderate heritability and relative independence of K dyn indicates that this measurement could be used successfully in a breeding programme to improve shell quality and to reduce the incidence of cracks.

Distribution and Regulation by Oestrogen of Fully Processed and Variant Transcripts of Gonadotropin Releasing Hormone I and Gonadotropin Releasing Hormone Receptor mRNAs in the Male Chicken

The aim of this study was to increase understanding of the occurrence and regulation of chicken gonadotropin releasing hormone I (cGnRH I) and chicken gonadotropin releasing hormone receptor (cGnRH‐R) mRNA variants in the hypothalamic‐pituitary‐testicular axis (HPTA). The study was carried out in the cockerel. Fully processed cGnRH I mRNA (cGnRH Ia) and a variant transcript (cGnRH Ib) with a retained intron 1 were observed in the preoptic/anterior hypothalamus (POA), the basal hypothalamus, anterior pituitary gland, and testes. Fully processed cGnRH‐R mRNA (cGnRH‐Ra) and a variant transcript (cGnRH‐Rb) with a deletion were detected in the same tissues. In juvenile cockerels, concentrations of cGnRH Ia and b in the POA increased after castration, and this was prevented by oestrogen treatment. In the anterior pituitary gland, the concentration of cGnRH‐Ra increased after castration and this was reversed by oestrogen treatment. In intact adult cockerels, oestrogen treatment depressed plasma luteinizing hormone but did not affect concentrations of cGnRH I and cGnRH‐R mRNAs in the POA, basal hypothalamus, and anterior pituitary gland, suggesting that locally produced oestrogen, by aromatization, may exert maximal suppression on cGnRH I and GnRH‐R mRNAs. In intact adult cockerels, the concentrations of cGnRH Ia and b in the testis, but not cGnRH‐Ra and b, were depressed by oestrogen treatment. It was concluded that fully processed and variant cGnRH I and cGnRH‐R mRNAs occur in all components of the HPTA. Oestrogen appears to play a role in the regulation of cGnRH Ia and b in the POA and testes, and of cGnRH‐Ra in the POA and anterior pituitary gland.

Polymorphisms in eggshell organic matrix genes are associated with eggshell quality measurements in pedigree Rhode Island Red hens

Novel and traditional eggshell quality measurements were made from up to 2000 commercial pedigree hens for a candidate gene association analysis with organic eggshell matrix genes: ovocleidin-116, osteopontin (SPP1), ovocalyxin-32 (RARRES1), ovotransferrin (LTF), ovalbumin and ovocalyxin-36, as well as key genes in the maintenance and function of the shell gland [estrogen receptor (ESR1) and carbonic anhydrase II (CAII)]. Associations were found for (i) ovalbumin with breaking strength and shell thickness; (ii) ovocleidin-116 with elastic modulus, shell thickness and egg shape; (iii) RARRES1 with mammillary layer thickness; (iv) ESR1 with dynamic stiffness; (v) SPP1 with fracture toughness and (vi) CAII with egg shape. The marker effects are as large as 17% of trait standard deviations and could be used to improve eggshell quality.

Changes in basal hypothalamic chicken gonadotropin-releasing hormone-I and vasoactive intestinal polypeptide associated with a photo-induced cycle in gonadal maturation and prolactin secretion in intact and thyroidectomized starlings (Sturnus vulgaris)

Chicken gonadotropin‐releasing hormone‐I (GnRH‐I) and the avian prolactin‐releasing hormone, vasoactive intestinal polypeptide (VIP), were measured in the basal hypothalamus in male starlings during photo‐induced gonadal growth and the subsequent development and maintenance of reproductive photorefractoriness. Comparisons were made with thyroidectomized birds, which maintain breeding condition irrespective of changes in photoperiod. In intact birds, basal hypothalamic GnRH‐I increased four‐fold after photostimulation and then decreased 115‐fold over 12 weeks to values characteristic of long‐term photorefractoriness. Pituitary and plasma prolactin increased after photostimulation, reaching peak values when the testes were regressing, and returned to low values in long‐term photorefractory birds. Basal hypothalamic VIP did not change after photostimulation in intact birds. In photostimulated thyroidectomized birds, values for basal hypothalamic GnRH‐I and VIP, and for pituitary and plasma prolactin, remained no different to those of nonphotostimulated intact birds. These observations confirm that reproductive photorefractoriness is related to a decrease in hypothalamic GnRH‐I. However, photorefractoriness in terms of prolactin secretion is not similarly related to a decrease in basal hypothalamic VIP. The mechanisms responsible for the decrease in prolactin in long‐term photorefractory birds and for the total lack of photoperiodic responses in thyroidectomized birds remain unresolved.

New hypotheses on the function of the avian shell gland derived from microarray analysis comparing tissue from juvenile and sexually mature hens.

Activation of the shell gland region of the avian oviduct is mediated by ovarian steroids. To understand more extensively how shell glands are maintained and function, we have compared gene expression in the shell glands from juvenile and laying hens using a chicken cDNA microarray. Average expression profiles of juvenile and sexually mature shell glands were compared resulting in the identification of 266 differentially regulated genes. Reverse transcription quantitative polymerase chain reaction confirmed expression differences. The differentially expressed genes included several with known involvement in shell gland function, including ion transport and shell matrix proteins. There were also many unpredicted differentially expressed genes, and for some we propose hypotheses for their functions. These include those encoding (a) osteoprotegerin, a decoy death receptor for receptor activator of nuclear factor NFkB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), that in the shell gland, may prevent apoptosis and/or may have an endocrine effect by preventing RANKLs action on bone osteoclasts that mobilize stored calcium; (b) prostatic acid phosphatase (ACPP) and prostate stem cell antigen (PSCA) that could play a role in sperm physiology within the shell gland; (c) urea transporter (SLC14A2) that could provide a novel anti-microbial defence; (d) bactericidal/permeability-increasing protein-like 2 (BPIL2), and other potential anti-microbials that have not previously been documented in the chicken. These new hypotheses, if borne out experimentally, will lead to a greater understanding of shell gland function including the processes involved in eggshell formation and anti-microbial activity.

A study of association between genetic markers in candidate genes and reproductive traits in one generation of a commercial broiler breeder hen population

Markers of alleles for three physiological candidate genes for reproductive traits, growth hormone (GHR), gonadotropin-releasing hormone receptor (GNRHR) and neuropeptide Y (NPY) were assessed for the association with the total egg production, number of double-yolked eggs and age at first egg in a single generation of a broiler breeder (Gallus gallus) pedigree dam line. Single-nucleotide polymorphisms and deletions were detected in the GHR, GNRHR and NPY genes. Genotypes were identified using a PCR-RFLP assay. The frequency of restriction enzyme+/−alleles in the population was for GHR 0.68 (NspI−) and 0.32 (NspI+), for NPY 0.78 (DraI+) and 0.22 (DraI−) and for GNRHR 0.54 (Bpu1102I+) and 0.46 (Bpu1102I−). Trait data from a total of 772 hens in 67 sire families from one generation of the pedigree dam line were recorded. However, the analysis used only the offspring of heterozygous sires to reduce the influence of selection and genetic background (n=33 sire families for GHR; n=14 sire families for NPY; n=36 sire families for GNRHR). A dominance effect of NPY on age at first egg and an additive effect of GNRHR on the number of double-yolked eggs were found (P<0.05).

Cellular localization of neuropeptide Y mRNA and peptide in the brain of the Japanese quail and domestic chicken

Abstractu2002Neuropeptide Y (NPY) has been implicated in the control of a number of physiological functions in birds including food intake and reproduction. In the present study, sites of NPY synthesis were localized in the brains of Japanese quail and domestic chickens by in situ hybridization histochemistry using a digoxigenin-labelled riboprobe. NPY mRNA was detected in three main cell groups in both species. The most prominent group was associated with structures in the lateral thalamus including the anterior lateral thalamic nucleus, lateral forebrain bundle, rotund nucleus, pretectal nucleus and occipitomesencephalic tract. Other major cell groups were detected in the hippocampus, and in the caudal linear nucleus and raphe nucleus of the brainstem. NPY mRNA was also present in the piriform cortex and taenial nucleus. Double-labelling of NPY mRNA and peptide was demonstrated in individual cells of the hippocampal, thalamic and brainstem cell groups, suggesting that NPY is synthesized and stored in these areas. However, the identity of other cell groups, notably in the hyperstriatal, archistriatal and neostriatal regions of the telencephalon, which exhibit NPY-immunoreactive cell bodies but no NPY mRNA, remains to be determined.