Parameters of the chicken genome (Gallus gallus)

As more information on the chicken genome is gathered, it is becoming increasingly more important to be able to correlate genetic and physical maps. Quantitation of the chicken karyotype is important in establishing parameters which define the genome. Here we report on the physical lengths of the chicken macrochromosomes and establish the DNA content of each, thus identifying implicitly how much of the genome is represented by the microchromosomal component. For the first time, genetic and physical data on the chicken karyotype are presented in relation to one another.     

Cardiovascular regulation during hypoxia in embryos of the domestic chicken Gallus gallus

Renewed interest in the use of the embryonic chicken as a model of perinatal cardiovascular regulation has inspired new questions about the control mechanisms that respond to acute perturbations, such as hypoxia. The objectives of this study were to determine the cardiovascular responses, the regulatory mechanisms involved in those cardiovascular responses, and whether those mechanisms involved the central nervous system (CNS) of embryonic chickens. Heart rate (f(H)) and blood pressure were measured in chicken embryos of different incubation ages during exposure to different levels of hypoxia (15, 10, and 5% O(2)). At all levels of hypoxia and at all developmental ages, a depression of f(H) and arterial pressure was observed, with the exception of day 20 embryos in 15 and 10% O(2). The intensity of the embryonic f(H) and blood pressure responses were directly related to the level of hypoxia used. Muscarinic and alpha-adrenergic receptor stimulation limited the hypoxic hypotension on days 15-19 and 15-21, respectively, as indicated after blockade with atropine and phentolamine. During the final 3 days of incubation, the intensity of the hypoxic hypotension was magnified due to alpha-vasodilation caused by beta-adrenergic and muscarinic receptor stimulation. In 19- to 21-day-old embryos, the f(H) response to hypoxia was limited by alpha-adrenergic receptor stimulation as indicated by the accentuated bradycardia after blockade with phentolamine. Furthermore, on day 21, atropine limited the hypoxic bradycardia, indicating that muscarinic receptors also play a role in the f(H) response at this age. In addition, the muscarinic actions on the heart and the adrenergic effects on the vasculature appeared to occur through a hypoxic-induced direct release from chromaffin tissue and autonomic nerve terminals. Thus, in embryonic chickens, the only cardiovascular response to hypoxia that involves the CNS was the cholinergic regulation of arterial pressure after day 15 of incubation. Therefore, although embryonic chickens and fetal sheep, the standard models of perinatal cardiovascular physiology, respond to hypoxia with a similar redistribution of cardiac output, the underlying mechanisms differ between these species.     

Neurogenic inflammation in the chicken (Gallus gallus var domesticus)

1. Neurogenic inflammation has been studied in the anaesthetized adult hen using a variety of different stimuli.2. Plasma extravasation was produced following antidromic stimulation of the external mandibular ramus of the trigeminal nerve which innervates the skin at the angle of the jaw and the anterior part of the wattle.3. Stimulation of the wattle by external application of mustard oil, thermal and mechanical stimuli, as well as intradermal injection of substance P and bradykinin, all produced plasma extravasation.4. These results demonstrate that, in contrast to previous findings in the pigeon, at least in the trigeminal of the chicken peripheral C-fibre nociceptors have similar physiological characteristics in relation to the neurogenic inflammatory mechanism to those seen in mammals.     

The effects of corticosterone and catecholamine infusion on plasma glucose levels in chicken (Gallus domesticus) and Turkey (Meleagris gallapavo)

1. Continuous 5hr infusion of low levels of corticosterone, epinephrine, isoproterenol or phenylephrine plus a high dose bolus injection at 3 hr had different effects on the plasma glucose levels of chickens and turkeys.2. Corticosterone had no effect on plasma glucose in turkeys, but increased glucose after the bolus and at 270 and 300 min for chickens.3. Epinephrine increased plasma glucose in turkeys, but only caused a transient elevation after the bolus in chickens.4. Isoproterenol increased plasma glucose in turkeys, but had no effect in chickens.5. Phenylephrine increased plasma glucose after the bolus in turkeys but had no effect in chickens.     

Development of drinking mechanisms in the chicken (Gallus gallus) (Aves)

Summary Development of the drinking mechanism from the day of hatching to the 4 week old chick was studied in relation to the growth of the oropharynx and drinking performance. Results indicate that due to scaling effects in the growing oropharynx, physical factors require the development of extra mechanisms. The swallowing mechanism to transport water from the pharynx into the esophagus during the tip up phase is already present in hatchlings, and does not change during ontogeny. The mechanism for water intake during the immersion phase changes considerably. Hatchlings display pecking behavior towards water. Week old chicks protrude the tongue far out, and the total volume ingested is sucked up by capillary action between the tongue, the floor, and the roof of the oropharynx. In 2 and 3 week old chicks the relative distance over which water is sucked up by capillarity decreases, whereas the volume of water pushed caudad by the tongue and bills increases. Laryngeal suction also develops in this period. At the age of 4 weeks chickens use the adult mechanism to drink. Most oropharyngeal elements increase two to three times in length and width during post hatching ontogeny. Due to these increases, water transport by capillarity alone does not suffice in the older age groups; therefore additional mechanisms such as pressure development by closing the bills and laryngeal suction must develop. Relative to the oropharyngeal length most elements grow isometrically. The width of the lingual alae and the larynx width, however, increase with positive allometry, which improves both capillary action as well as the transport of water during the tip up phase when the chicks grow older. The need to develop extra water transport mechanisms during growth due to scaling effects is shown to condition the radiation capacity of avian drinking mechanisms. Nidicolous birds are, however, not constrained by the need to have a properly operating drinking mechanism during the early ontogeny and may therefore have a better chance of developing alternativ drinking mechanisms then nidifugous birds.     

Systematic identification and characterization of chicken (Gallus gallus) ncRNAs

Recent studies have demonstrated that non-coding RNAs (ncRNAs) play important roles during development and evolution. Chicken, the first genome-sequenced non-mammalian amniote, possesses unique features for developmental and evolutionary studies. However, apart from microRNAs, information on chicken ncRNAs has mainly been obtained from computational predictions without experimental validation. In the present study, we performed a systematic identification of intermediate size ncRNAs (50–500 nt) by ncRNA library construction and identified 125 chicken ncRNAs. Importantly, through the bioinformatics and expression analysis, we found the chicken ncRNAs has several novel features: (i) comparative genomic analysis against 18 sequenced vertebrate genomes revealed that the majority of the newly identified ncRNA candidates is not conserved and most are potentially bird/chicken specific, suggesting that ncRNAs play roles in lineage/species specification during evolution. (ii) The expression pattern analysis of intronic snoRNAs and their host genes suggested the coordinated expression between snoRNAs and their host genes. (iii) Several spatio-temporal specific expression patterns suggest involvement of ncRNAs in tissue development. Together, these findings provide new clues for future functional study of ncRNAs during development and evolution.     

Genetic characterization of Bhutanese native chickens based on an analysis of Red Junglefowl (Gallus gallus gallus and Gallus gallus spadecieus), domestic Southeast Asian and commercial chicken lines (Gallus gallus domesticus)

The genetic diversity of Bhutanese chickens needs to be understood in order to develop a suitable conservation strategy for these birds in Bhutan. In this, work, we used microsatellite markers to examine the genetic diversity of Bhutanese chickens. Four Bhutanese chicken varieties (Black plumage, Frizzle, Naked neck and Red Junglefowl-like, corresponding to Yuebjha Narp, Phulom, Khuilay and Seim, respectively), two subspecies of Red Junglefowl (Gallus gallus gallus and Gallus gallus spadecieus), two varieties of Thai native chickens (Pradhu Hang Dam and Chee; Gallus gallus domesticus) representing the Southeast Asian domestic chicken, and two commercial lines (Broiler and Single Comb White Leghorn) were genotyped with 18 microsatellites that included 16 loci recommended by the FAO/ISAG for investigations of genetic variability in chickens. All loci were polymorphic, with the number of alleles ranging from six (MCW0111) to 23 (MCW0183). Substantial genetic variation was observed in all populations, with the Bhutanese native chicken Yuebjha Narp (Black plumage chicken) showing the lowest genetic variability. Despite extensive intrapopulation variation, the genetic differentiation among 10 populations was moderate. A neighbor-joining tree revealed the genetic relationships involved while principal component analysis showed that Bhutanese native chickens should be given priority in conservation efforts because of their genetic distinctiveness. Chee chickens are especially valuable as a reservoir of predomestic diversity, as indicated by their greater genetic variation and their position in the phylogenetic tree.     

Brush-like cells within bronchial epithelia of chicken lung (Gallus gallus)

The secondary and primary (mesobronchus) bronchi of chicken lung are lined by a typical respiratory epithelium: pseudostratified columnar ciliated with goblet cells. Up to date, four constituting epithelial cell types have been identified: ciliated, mucosecretory, basal and endocrine cells. In this study a putative new epithelial cell type, the brush-like cell, is described. The avian brush-like cells have only been found in the bronchial epithelia but never in the gas-exchange areas. They are scattered among the other epithelial cells, mainly ciliated cells, and their number is extremely low. The characteristic morphological feature of these cells is an apical protruding cytoplasm with microvilli. This cell type is similar to that found in the lung of some mammalian and non-mammalian species. The functional role of these cells is not yet clear; they could carry out absorptive processes.     

Development of cholinergic chronotropic control in chick (Gallus gallus domesticus) embryos

In chick (Gallus gallus domesticus) embryos, instantaneous heart rate begins to fluctuate with the appearance of rapid, transient decelerations at around the end of the second week of incubation. Previously, it was shown that instantaneous heart rate decelerations were eliminated by administration of atropine and concurrently heart rate baseline was elevated in late embryos. Because the previous study lacked statistical treatment and there has been recent controversy over the development of tonic vagal control of the heart, we reexamine the hypothesis that transient decelerations of instantaneous heart rate are mediated by vagus nerve and the vagal tone begins to appear at around the end of the second week of incubation. Atropine administration tests were conducted for sixty-seven 11- to 14-day-old and 18-day-old embryos in total. Heart rate decelerations appeared sporadically in three out of ten 12-day-old embryos, but the difference of mode heart rate before and after administration of atropine was not significant. Seven out of nine 13-day-old embryos and all nine 14-day-old embryos showed heart rate decelerations and the difference of mode heart rate before and after atropine administration was significant. In late (18-day-old) embryos, magnitude and frequency of instantaneous heart rate decelerations further increased with additional appearance of transient, irregular accelerations. Administration of varying doses of atropine completely eliminated the heart rate decelerations and elevated the heart rate baseline more markedly than in young embryos, indicating the maturation of vagal tone late in incubation.     

Chromosome abnormalities in early chicken (Gallus domesticus) embryos

Chromosome studies were undertaken to determine if early embryonic mortality in chicken (Gallus domesticus) embryos is associated with chromosome aberrations. A rapid cytological technique was developed for screening large numbers of embryos for euploidy and aneuploidy. — Of 115 embryos examined, 6 or 5.2% had aberrant chromosome complements. All of these chromosome aberrations occurred in embryos that were phenotypically abnormal. Of 45 macroscopically abnormal embryos, 13.3 % were chromosomally aberrant. These included two cases of haploidy (A-Z), one case of trisomy-1, a case of trisomy-2 and two cases of triploidy (3A-ZZW and 3A-ZWW). — Possible modes of origin for euploid and aneuploid embryos are discussed and consideration given to the significance of these aberrations in relation to embryo viability, constancy of chromosome numbers and nucleolar organization.     

Relationship between the saccus endolymphaticus and the fourth ventricle of the brain of the domestic fowl (Gallus gallus f. domestica)

The fine structure of the wall of the SE was determined exactly and its relationship to the cisternae (the evaginations of the roof of the fourth ventricle extending to the SE) was defined. The way in which the cisterna is formed was defined and the development of its fine structure was described by comparing serial sections from 19-day embryos and adult fowls. Like the SE, the cisternae are lodged in the angle between the cerebellum and the medulla oblongata, in the subarachnoid space. The terminal segment of the cisterna lies in the immediate vicinity of the mesenchymal epithelium bordering the basal labyrinth of the SE cells. Collagen trabeculae keep the SE and the cisternae suspended in the subarachnoid space. The cisternae and trabeculae are wrapped in mesenchymal epithelium. The cisterna is avascular and does not communicate with the SE. The cisterna is lined internally with simple squamous epithelium (modified neural epithelium of the roof of the fourth ventricle). The bodies of the cells bulge into the lumen of the cisterna in the region of localization of their nucleus. The epithelium is seated on a pronounced basal lamina. The surface turned towards the subarachnoid space is lined continuously with mesenchymal epithelium without a basal lamina. The cells of the cisternal epithelium are connected by tight junctions of the type of zonulae occludentes and desmosomes. The basal lamina is continuous and distinct. The mesenchymal epithelium of the subarachnoid space has no basal lamina, as on the subarachnoid surface of the SE, the cisternae, the trabeculae, the pia mater and the arachnoidea.(ABSTRACT TRUNCATED AT 250 WORDS)     

Control of blood pressure mediated by baroreflex changes of heart rate in the chicken embryo (Gallus gallus)

Pharmacological manipulation of peripheral resistance via sodium nitroprusside and phenylephrine was used to study baroreflex function over the latter two-thirds of incubation in embryonic chickens. From day 9 to day 19 of incubation, there is a positive linear relation between heart rate and blood pressure, indicating the feedforward action of arterial pressure on heart rate. A reciprocal relationship between blood pressure and heart rate became pronounced during the last 3 days of incubation. For the purpose of the study, gain of the baroreflex was calculated as maximal gain (only those embryos that demonstrated the response) or average gain (all embryos). Maximal gain increased progressively from 13 +/- 7 beats. min(-1). kPa(-1) at 18 days to 105 +/- 83 beats. min(-1). kPa(-1) in 2-day-old hatchlings. The percentage of embryos older than 18 days with baroreflex responses increased from 33% on day 19 to 56% on day 21, indicating that baroreflex regulation begins late in incubation ( approximately 90% incubation time), and the gain of this reflex exhibits a maturation over the final 3 days of incubation.     

Sex inversion in domestic chicken (Gallus gallus domesticus) by letrozole and tamoxifen

In multicellular organisms, determination of sex identity is a complex, multistage process. Sex hormones are synthesized in gonads and fulfill the role of inductors in this process. The effect of androgen is currently well studied. However, the participation of estrogen in the formation of female gonads and female sex on the whole is not much known. Here, we present the results of experimental sex inversion by inhibition of aromatase (an enzyme involved in estrogen synthesis) and tamoxifen (a modulator of estrogen receptors) in chick embryos. It was shown that masculinization depended on the dose of the substance and quantity of injections. Inhibition of aromatase did not block the meiotic prophase in oogoniums. It has been suggested that retinoic acid and estrogens have different mechanisms of effect on oogenesis. Proteins and nucleoproteins interacting with estrogen receptor 1 and their gene localization in human and chicken genomes have been shown for the first time.     

Mitochondrial DNA sequence and haplotype variation analysis in the chicken (Gallus gallus)

Although it is known to be useful for certain genotype:phenotype assignments, our knowledge of the nature and extent of variation in the entire chicken (Gallus gallus) mitochondrial genome (mtGenome) is limited. Here, we used experimental and in silico tools to identify nucleotide variants in the mtGenome, including the coding and non-coding (D-loop) regions. The distribution of the experimentally identified mitochondrial DNA variants in meat- (broilers) and egg-type (White Leghorn) chickens was also assessed. A total of 113 single-nucleotide polymorphisms (SNPs) were identified. The in silico analysis revealed a total of 91 SNPs, with 70 in the coding region and 21 in the non-coding region. Of the 41 experimentally identified SNPs, 27 were in the D-loop. Together, the experimentally identified SNPs in the non-coding region formed 11 haplotypes, whereas the 14 SNPs in the coding region formed 6. Though, 9 of the D-loop region haplotypes were observed only in broilers, 3 of the 6 haplotypes from the coding region occurred at a significantly higher frequency in broilers. To our knowledge, this investigation represents the first whole-mtGenome scan for variation and an evaluation, though limited in sample size, of the haplotype distribution in meat- and egg-type populations, using the SNPs and haplotypes identified.     

Cell number and sex ratio in unfertilized chicken eggs (Gallus gallus domesticus)

In chickens and other birds, females have two different sex chromosomes (ZW), whereas males carry two homologous sex chromosomes (ZZ). The primary sex ratio can thus be determined by genetic analysis of the sex chromosome of the ovum before fertilization. Sex diagnosis is more reliable when there are more cells, i.e. sufficient DNA, for the analysis. In this study, eggs from virgin hens were incubated for 3 days and the number of cells in the germinal discs was counted. A median of 2.5 cells was counted with a range of two to 20 cells. We also counted cells in the germinal discs of unfertilized eggs of inseminated hens and recorded a median of three cells and a range of two to 40 cells. Sex diagnosis based on polymerase chain reaction (PCR) amplification of Z and W chromosomes specific fragments from the CHD1 gene in 30 incubated eggs obtained from 35-week-old virgin hens gave a ratio of 13 Z to 15 W chromosomes with two samples undetermined.The unfertilized eggs of three groups of chickens were subjected to sex diagnosis to supplement the sex ratio data of an incubation experiment (see companion paper). The high proportion of Z chromosomes diagnosed in all three groups by two independent gene products suggests a sex difference on developmental potential and/or a sex chromosome segregation biased toward males in unfertilized eggs especially at the beginning of reproduction.