Sperm replacement in sperm-storage tubules causes last-male sperm precedence in chickens

1. This study elucidated the last-male sperm precedence (LMSP) mechanism in chickens by examining replacement in storage tubules (SSTs) after multiple artificial inseminations (AI) and the effects of seminal plasma (SP) and male breed on sperm replacement in SSTs.2. Hens were artificially inseminated with fluorescent dye-labelled spermatozoa from White Leghorn (WL) chickens. Secondary AI was conducted 3 d later with sperm labelled with different nuclear fluorescent dye. Percentage of first and second inseminated sperm in SSTs and their logarithmic odds were calculated. The effect of SP on LMSP was examined using (1) Lake's solution-washed sperm before second insemination, and (2) SP injected continuously after first insemination. Effect of breed difference on sperm replacement was investigated using Barred Plymouth Rock (BP) sperm.3. Successive WL-sperm inseminations at three-day intervals caused > 70% stored sperm replacement in SSTs. Although SP removal from sperm from second insemination significantly decreased replacement, its intra-vaginal injection did not affect release. Secondary insemination using BP sperm significantly increased replacement.4. Sperm replacement is a major factor favouring LMSP in domestic chickens. Two fluorescent staining of sperm, and intra-vaginal multiple AI technique have enabled visualisation, differentiation, and quantification of multiple inseminated sperm stored in the SSTs.

Quantitative trait loci mapping of innate fear behavior in day-old F2 chickens of Japanese Oh-Shamo and White Leghorn breeds using restriction site-associated DNA sequencing

Understanding the genetic mechanisms that underlie innate fear behavior is essential for improving the management and performance of the poultry industry. This study aimed to map QTL associated with innate fear responses in open field (OF) and tonic immobility (TI) tests, using an F2 chicken intercross population between 2 behaviorally distinct breeds: the aggressive Japanese Oh-Shamo (OSM) and the docile White Leghorn T-line (WL-T). Genome-wide QTL analysis for the OF and TI traits was conducted using 2,109 single nucleotide polymorphism (SNP) markers obtained through restriction site-associated DNA sequencing (RAD-seq). While several suggestive QTL were identified for TI and OF traits at genome-wide 20% significance threshold levels, the analysis revealed 2 significant QTL for 2 OF traits (total distance and maximum speed) at genome-wide 5% significance threshold levels. These significant QTL were located between 12.34 and 30.49 megabase (Mb) on chromosome 1 and between 40.02 and 63.38 Mb on chromosome 2, explaining 6.75 to 7.40% of the total variances. These findings provide valuable insights for the poultry industry, particularly in refining chicken management strategies and informing targeted breeding efforts.

Association analysis of production traits of Japanese quail (Coturnix japonica) using restriction-site associated DNA sequencing

This study was designed to perform an association analysis and identify SNP markers associated with production traits of Japanese quail using restriction-site-associated DNA sequencing. Weekly body weight data from 805 quail were collected from hatching to 16 weeks of age. A total number of 3990 eggs obtained from 399 female quail were used to assess egg quality traits. Egg-related traits were measured at the beginning of egg production (first stage) and at 12 weeks of age (second stage). Five eggs were analyzed at each stage. Traits, such as egg weight, egg length and short axes, eggshell strength and weight, egg equator thickness, yolk weight, diameter, and colour, albumen weight, age of first egg, total number of laid eggs, and egg production rate, were assessed. A total of 383 SNPs and 1151 associations as well as 734 SNPs and 1442 associations were identified in relation to quail production traits using general linear model (GLM) and mixed linear model (MLM) approaches, respectively. The GLM-identified SNPs were located on chromosomes 1-13, 15, 17-20, 24, 26-28, and Z, underlying phenotypic traits, except for egg and albumen weight at the first stage and yolk yellowness at the second stage. The MLM-identified SNPs were positioned on defined chromosomes associated with phenotypic traits except for the egg long axis at the second stage of egg production. Finally, 35 speculated genes were identified as candidate genes for the targeted traits based on their nearest positions. Our findings provide a deeper understanding and allow a more precise genetic improvement of production traits of Galliformes, particularly in Japanese quail.

New Behavioral Handling Test Reveals Temperament Differences in Native Japanese Chickens

It is well known in the poultry industry that fear and stress experienced during the handling of day-old chicks in commercial hatcheries can have long-lasting effects on their behavior later in life. These hatchery-related stresses are more intense and complex than those encountered in traditional behavioral tests. Consequently, a single behavioral test may not be sufficient to measure hatchery stresses and chicken temperament. In this study, we developed a new behavioral handling test for day-old chickens, which incorporated concepts from established behavioral tests used with both young and adult birds. The new test assessed 10 behavioral traits, including vocalization frequency and responses to human interaction. It was conducted on 96 two-day-old chicks from seven breeds of native Japanese and Western chickens. The results of the principal component analysis classified chicken temperaments into three distinct categories: bustle, aggression, and timidity. Using these categories, the seven breeds were classified into five groups, each with distinct temperaments. This study highlights the reliability and value of the new handling test in characterizing the temperaments of various chicken breeds and provides insights into the complex behaviors of chickens.

Differences in innate fear behaviour in native Japanese chickens

1. Comprehensive knowledge of innate fear in chickens has important implications for understanding the adaptation of native Japanese chickens in modern production and behavioural changes caused by modern breeding goals. Innate fear behaviour seen in chicks from six native Japanese chicken breeds;, Ingie (IG), Nagoya (NAG), Oh-Shamo (OSM), Tosa-Jidori (TJI), Tosa-Kukin (TKU) and Ukokkei (UK), were compared with those in two lines of White Leghorn (WL-G and WL-T) in tonic immobility (TI) and open field (OF) tests.2. TI and OF tests were conducted for 267 chicks at 0-1 days of age in the eight breeds. Raw data for four TI traits and 13 OF traits were corrected for environmental factors. Breed differences were analysed by the Kruskal-Wallis test followed by the Steel Dwass post hoc test. Principal component (PC) analyses were conducted.3. The results showed that OSM was the least sensitive to fear in both the TI and OF tests. The WL-G birds showed higher sensitivity to TI fear but lower sensitivity to OF fear. The PC analysis of OF traits classified the tested breeds into three groups: least (OSM and WL-G), moderate (IG, WL-T, NAG, TJI and TKU) and most sensitive (UK).

Development of cryopreservation media for the slow-freezing of cultured primordial germ cells in chicken

Conservation of chicken germplasm is crucial in supporting commercial breeds for sustainable egg and meat production and preserving the genetic diversity of indigenous breeds for future breeding. Cryopreservation of chicken fertilized eggs or embryos is not feasible, owing to the large yolk-laden structure of the eggs. Primordial germ cells (PGCs), the embryonic precursors of gametes, are the best candidates for the cryobanking of chicken germplasm. Effective cryobanking of chicken PGCs requires an optimal cryopreservation protocol. Cryomedia containing dimethyl sulfoxide (DMSO) or DMSO combined with serum have been widely used for the cryopreservation of chicken PGCs. However, as cryoprotectants are yet to be optimized for chicken PGCs, the efficacy of cryomedia can be further improved. Here, we investigated the cryoprotective effects of propylene glycol (PG), an alternative to DMSO, on chicken PGCs. We found that the addition of non-permeable cryoprotectants, such as trehalose or chicken serum, to DMSO or PG cryomedia improved the recovery and survival rates of post-thawed PGCs. We further investigated the cryoprotective effects of trehalose and chicken serum and found that these additives have different cryoprotective actions. Based on these findings, we designed two different cryomedia: DTS, including 5% DMSO, 0.3 M trehalose, and 1% chicken serum, and PTS, including 7.5% PG, 0.1 M trehalose, and 5% chicken serum. Among the different PGC lines and freshly isolated PGCs, the cryomedia showed similar post-thaw recovery rates. Following transplantation, post-thawed male PGCs can colonize gonads and differentiate into functional sperm. We successfully revived the offspring of Kurokashiwa, a rare chicken breed in Japan, with cryopreserved PGCs. In conclusion, we developed two different cryomedia that achieved > 50% recovery of viable PGCs after thawing while maintaining germline competency.

5-aminolevulinic acid improves chicken sperm motility

Objective

This study investigated the effects of 5-aminolevulinic acid (5-ALA) on the motility parameters, mitochondrial membrane depolarization, and ATP levels in chicken sperm.

Methods

The pooled semen from Barred Plymouth Rock males was used. In the first experiment, the semen was diluted 4-times with phosphate-buffered saline (PBS (-)) containing various concentrations (0, 0.01, 0.05, and 0.1 mM) of 5-ALA, and then the sperm motility parameters after incubation were evaluated by computer-assisted sperm analysis (CASA). In the second experiment, the semen was diluted 4-times with PBS (-) containing 0.05 mM 5-ALA, and then sperm mitochondrial membrane depolarization and ATP levels after 1.5 h of incubation were analyzed with the MitoPT® JC-1 Assay and ATP Assay kits, respectively. In the third experiment, the semen was removed from the seminal plasma and resuspended with the mediums of PBS (-), PBS (-) supplemented with CaCl2 and MgCl2 (PBS (+)) + 5-ALA, PBS (+) + caffeine, and PBS (+) + caffeine + 5-ALA. Then, the sperm motility parameters after incubation were evaluated by CASA. In the last experiment, the semen was treated with the mediums of PBS (-), PBS (-) + 5-ALA, 5.7% glucose, 5.7% glucose + 5-ALA after removing the seminal plasma, and then the sperm motility parameters were evaluated by CASA.

Results

The addition of 0.05 mM 5-ALA significantly increased the chicken sperm motility, progressive motility, linearity, average path velocity, curvilinear velocity, straight-line velocity, and the wobble. The sperm mitochondrial membrane depolarization was also increased by the 5-ALA treatment. The 5-ALA treatment decreased the sperm ATP levels. Both the caffeine treatment and glucose treatment decreased the sperm motility during incubation period.

Conclusion

5-ALA might increase sperm mitochondrial membrane depolarization to utilize the ATP for enhancing sperm movement.

Longer and faster sperm exhibit better fertilization success in Japanese quail

In birds, sperm storage tubules (SST) located in the utero-vaginal junction are thought to be a site of sperm selection; however, the exact mechanism of sperm selection is poorly understood. Here, we investigated sperm entry into the SST and subsequent fertilization success under a competitive situation created by artificial insemination of a sperm mixture obtained from 2 males. We employed 2 quail strains, a wild-type and a dominant black (DB) type, as this allows easy assessment of paternity by feather coloration. We found paternity of embryos was biased toward DB males when a sperm mix with similar sperm numbers from the 2 males strains was artificially inseminated into females. Our novel sperm staining method with 2 different fluorescent dyes showed that the DB-biased fertilization was because of the better ability of DB sperm to enter the SST. Moreover, we found that DB sperm had a longer flagellum and midpiece. These characteristics probably allow sperm to swim faster in a high viscosity medium, which may be a similar environment to the lumen of the female reproductive tract. Our results indicated that sperm competition occurs to win a place in the SST and that filling the SST with their own spermatozoa is a critical step to achieve better fertilization success for the male Japanese quail.

Geographic Origin and Genetic Characteristics of Japanese Indigenous Chickens Inferred from Mitochondrial D-Loop Region and Microsatellite DNA Markers

Japanese indigenous chickens have a long breeding history, possibly beginning 2000 years ago. Genetic characterization of Japanese indigenous chickens has been performed using mitochondrial D-loop region and microsatellite DNA markers. Their phylogenetic relationships with chickens worldwide and genetic variation within breeds have not yet been examined. In this study, the genetic characteristics of 38 Japanese indigenous chicken breeds were assessed by phylogenetic analyses of mitochondrial D-loop sequences compared with those of indigenous chicken breeds overseas. To evaluate the genetic relationships among Japanese indigenous chicken breeds, a STRUCTURE analysis was conducted using 27 microsatellite DNA markers. D-loop sequences of Japanese indigenous chickens were classified into five major haplogroups, A-E, among 15 haplogroups found in chickens worldwide. The haplogroup composition suggested that Japanese indigenous chickens originated mainly from China, with some originating from Southeast Asia. The STRUCTURE analyses revealed that Japanese indigenous chickens are genetically differentiated from chickens overseas; Japanese indigenous chicken breeds possess distinctive genetic characteristics, and Jidori breeds, which have been reared in various regions of Japan for a long time, are genetically close to each other. These results provide new insights into the history of chickens around Asia in addition to novel genetic data for the conservation of Japanese indigenous chickens.

The formation of multiple pituitary pouches from the oral ectoderm causes ectopic lens development in hedgehog signaling-defective avian embryos

BACKGROUND

Hedgehog signaling has various regulatory functions in tissue morphogenesis and differentiation. To investigate its involvement in anterior pituitary precursor development and the lens precursor potential for anterior pituitary precursors, we investigated Talpid mutant Japanese quail embryos, in which hedgehog signaling is defective.

RESULTS

Talpid mutants develop multiple pituitary precursor-like pouches of variable sizes from the oral ectoderm (OE). The ectopic pituitary pouches initially express the pituitary-associated transcription factor (TF) LHX3 similarly to Rathke's pouch, the genuine pituitary precursor. The pouches coexpress the TFs SOX2 and PAX6, a signature of lens developmental potential. Most Talpid mutant pituitary pouches downregulate LHX3 expression and activate the lens-essential TF PROX1, leading to the development of small lens tissue expressing α-, β-, and δ-crystallins. In contrast, mutant Rathke's pouches express a lower level of LHX3, which is primarily localized in the cytoplasm, and activate the lens developmental pathway.

CONCLUSIONS

Hedgehog signaling in normal embryos regulates the development of Rathke's pouch in two steps. First, by confining Rathke's pouch development in a low hedgehog signaling region of the OE. Second, by sustaining LHX3 activity to promote anterior pituitary development, while inhibiting ectopic lens development.

Discovery of a new nucleotide substitution in the MC1R gene and haplotype distribution in native and non-Japanese chicken breeds

Melanocortin 1-receptor (MC1R) is one of the major genes that controls chicken plumage colour. In this study, we investigated the sequence and haplotype distribution of the MC1R gene in native Japanese chickens, along with non-Japanese chicken breeds. In total, 732 and 155 chickens from 30 Japanese and eight non-Japanese breeds respectively were used. Three synonymous and 11 non-synonymous nucleotide substitutions were detected, resulting in 15 haplotypes (H0-H14). Of these, three were newly found haplotypes (H9, H13 and H14), of which one (H9) was composed of known substitutions C69T, T212C, G274A and G636A. The second one (H13) possessed newly found non-synonymous substitution C919G, apart from the known substitutions C69T, G178A, G274A, G636A and T637C. The third one (H14) comprised a newly discovered substitution C919G in addition to the known C69T, G274A and G409A substitutions. The homozygote for this new haplotype exhibited wt like plumage despite the presence of G274A. In addition to discovering a new nucleotide substitution (C919G) and three new haplotypes, we defined the plumage colour of the bird that was homozygous for the A644C substitution (H5 haplotype) as wheaten-like for the first time; although the substitution has been already reported, its effect was not revealed. Besides detecting the new plumage colour, we also confirmed that the A427G and G274A substitutions contribute in expressing brownish and black plumage colour respectively, as reported by the previous studies. Moreover, we confirmed that the buttercup allele does not express black plumage despite possessing a G274A substitution, under the suppression effect of A644C. In contrast, the birds homozygous for the birchen allele presented solid black plumage, which was contradictory to the previous reports. In conclusion, we revealed a large diversity in the MC1R gene of native Japanese chicken breeds, along with the discovery of a new non-synonymous nucleotide substitution (C919G) and three novel haplotypes (H9, H13 and H14).

Quantitative trait loci mapping for the shear force value in breast muscle of F2 chickens

The shear force value is one of the major traits that determine meat quality. In the present study, we performed QTL analysis for chicken breast muscle shear force value at 7 wk of age using 545 single nucleotide polymorphism (SNP) markers developed via restriction-site associated DNA sequencing (RAD-seq). An F2 resource family was generated by mating Oh-Shamo, a native Japanese chicken breed, and the White Plymouth Rock chicken breed. A total of 215 F2 birds were produced. Simple interval mapping revealed one significant main-effect QTL between 6.28 and 8.10 Mb SNPs on the chromosome Z with a logarithm of odds score of 5.53 at the genome-wide 5% level. At this QTL, the confidence interval, phenotypic variance explained, and additive effect were 26 cM, 12.24%, and -0.31 in males and -0.34 in females, respectively. No QTL with epistatic interaction effects were detected. To our knowledge, this is the first report on a QTL affecting the shear force value in the chicken breast muscle, using SNP markers derived from RAD-seq.

Skeletal development in blue-breasted quail embryos

The blue-breasted quail (Coturnix chinensis), the smallest species of quail with short generation interval and excellent reproductive performance, is a potential avian research model. A normal series of skeletal development of avian embryos could be served as a reference standard in the fields of developmental biology and teratological testing as well as in the investigation of mutation with skeletal abnormalities and in the study of the molecular mechanisms of skeletal development through genome manipulation. Furthermore, ossification sequence shows a species-specific pattern and has potential utility in phylogeny. However, data on the skeletal development of blue-breasted quail embryos are scarce. Here, we established a series of normal stages for the skeletal development of blue-breasted quail embryos. Cartilage and ossified bones of blue-breasted quail embryos were stained blue and red with Alcian blue 8GX and Alizarin red S, respectively. The time and order of chondrification and calcification of their skeletons were documented every 24 hr from 3 to 17 days of incubation, and a 15-stage series of skeletal development was created. Moreover, a comparative study with the Japanese quail (Coturnix japonica) demonstrated that ossification sequence differed significantly between these two species.

Changes in prolactin receptor homodimer availability may cause late feathering in chickens

Chicken early (EF) and late feathering (LF) are sex-linked phenotypes conferred by wild-type k⁺ and dominant K alleles on chromosome Z, respectively. Besides prolactin (PRL) receptor (PRLR) and sperm flagellar 2 (SPEF2) genes, the K allele contains a fusion gene in which partially duplicated PRLR (dPRLR) and SPEF2 (dSPEF2) genes are linked in a tail-to-tail manner. The causative dPRLR gene encodes a C-terminal truncated receptor. LF chickens have short or no primaries at hatching; however, their feather growth rate is higher than that of EF chickens. This study aimed to elucidate the molecular basis of the K allele's biphasic effect on feather development. By 3'RACE and RT-PCR analyses, we demonstrated that dSPEF2 gene transcription occurred beyond all coding exons of the dPRLR gene on the opposite strand and that dPRLR mRNA was less abundant than PRLR mRNA. In addition, a 5'UTR splice variant (SPV) of PRL receptor mRNAs was increased in LF chickens. In vitro expression analysis of 5'UTR linked to the luciferase reporter gene revealed higher translation efficiency of SPV. RT-qPCR showed that the dPRLR mRNA level was higher in embryos; conversely, SPV was higher in hatched chickens, as was dSPEF2 mRNA. These findings suggest that the K allele inhibits feather development at the fetal stage by expressing dPRLR to attenuate PRLR function and promotes feather growth after hatching by increasing PRLR through dSPEF2 mRNA expression. Increased SPV may cause greater feather growth than that in EF chickens by increasing the availability of PRLR homodimers and enhancing PRL signaling.

Developmental stages of the blue-breasted quail (Coturnix chinensis)

Chickens and Japanese quail (Coturnix japonica) have traditionally been the primary avian models in developmental biology research. Recently, the blue-breasted quail (Coturnix chinesis), the smallest species in the order Galliformes, has been proposed as an excellent candidate model in avian developmental studies owing to its precocious and prolific properties. However, data on the embryonic development of blue-breasted quail are scarce. Here, we developed a normal developmental series for the blue-breasted quail based on developmental features. The blue-breasted quail embryos take 17 days to reach the hatching period at 37.7°C. We documented specific periods of incubation in which significant development occurred, and created a 39-stage developmental series. The developmental series for the blue-breasted quail was almost identical to that for chickens and Japanese quail in the earlier stages of development (stages 1-16). Our staging series is especially useful at later stages of development (stages 34-39) of blue-breasted quail embryos as a major criterion of staging in this phase of development was the weight of embryos and the length of third toes.

Endogenous viral gene ev21 is not responsible for the expression of late feathering in chickens

The late-feathering (LF) gene K on the Z chromosome is an important gene in the chicken industry, which is frequently utilized for the feather sexing, a type of autosexing, of neonatal chicks. The K gene is closely associated with the endogenous ev21 gene from an avian leukosis virus and the incomplete duplication (ID) of prolactin receptor (PRLR) and sperm flagellar protein 2 (SPEF2) genes, and ev21 has been used as a molecular marker to detect LF birds. In the present study, a comprehensive survey for the presence or absence of ev21 and ID across 1,994 birds from 52 chicken breeds, three commercial hybrid groups, and the Red Jungle Fowl revealed that almost all LF breeds have both ev21 and ID. However, only one LF breed (Ingie) has only ID and no ev21. Moreover, this study revealed that almost all early (normal)-feathering (EF) breeds lack both ev21 and ID, but only one breed (White Plymouth Rock) included EF birds with ev21 but no ID. Therefore, regarding LF expression, the results indicated that ID is responsible, but ev21 is not required. Henceforth, ID should be used as a molecular marker to detect LF birds instead of ev21. Because ev21 contains the full genome of an avian leukosis virus, there is a risk of disease development in breeds with this gene. Therefore, the Ingie breed, which has no ev21 at the K locus, represents excellent material for the establishment of new LF stocks.

Female Japanese quail visually differentiate testosterone-dependent male attractiveness for mating preferences

Biased mating due to female preferences towards certain traits in males is a major mechanism driving sexual selection, and may constitute an important evolutionary force in organisms with sexual reproduction. In birds, although the role of male ornamentation, plumage coloration, genetic dissimilarity, and body size have on mate selection by females have been examined extensively, few studies have clarified exactly how these characteristics affect female mate preferences. Here, we show that testosterone (T)-dependent male attractiveness enhances female preference for males of a polygamous species, the Japanese quail. A significant positive correlation between female mating preference and circulating T in the male was observed. The cheek feathers of attractive males contained higher levels of melanin and were more brightly colored. The ability of females to distinguish attractive males from other males was negated when the light source was covered with a sharp cut filter (cutoff; < 640 nm). When females were maintained under short-day conditions, the expression of retinal red-sensitive opsin decreased dramatically and they became insensitive to male attractiveness. Our results showed that female preference in quail is strongly stimulated by male feather coloration in a T-dependent manner and that female birds develop a keen sense for this coloration due to upregulation of retinal red-sensitive opsin under breeding conditions.

Genetic Mapping of Quantitative Trait Loci for Egg Production and Egg Quality Traits in Chickens: a Review

Chickens display a wide spectrum of phenotypic variations in quantitative traits such as egg-related traits. Quantitative trait locus (QTL) analysis is a statistical method used to understand the relationship between phenotypic (trait measurements) and genotypic data (molecular markers). We have performed QTL analyses for egg-related traits using an original resource population based on the Japanese Large Game (Oh-Shamo) and the White Leghorn breeds of chickens. In this article, we summarize the results of our extensive QTL analyses for 11 and 66 traits for egg production and egg quality, respectively. We reveal that at least 30 QTL regions on 17 different chromosomes affect phenotypic variation in egg-related traits. Each locus had an age-specific effect on traits, and a variety in effects was also apparent, such as additive, dominance, and epistatic-interaction effects. Although genome-wide association study (GWAS) is suitable for gene-level resolution mapping of GWAS loci with additive effects, QTL mapping studies enable us to comprehensively understand genetic control, such as chromosomal regions, genetic contribution to phenotypic variance, mode of inheritance, and age-specificity of both common and rare alleles. QTL analyses also describe the relationship between genotypes and phenotypes in experimental populations. Accumulation of QTL information, including GWAS loci, is also useful for studies of population genomics approached without phenotypic data in order to validate the identified genomic signatures of positive selection. The combination of QTL studies and next-generation sequencing techniques with uncharacterized genetic resources will enhance current understanding of the relationship between genotypes and phenotypes in livestock animals.

Inactivation of Sonic Hedgehog Signaling and Polydactyly in Limbs of Hereditary Multiple Malformation, a Novel Type of Talpid Mutant

Hereditary Multiple Malformation (HMM) is a naturally occurring, autosomal recessive, homozygous lethal mutation found in Japanese quail. Homozygote embryos (hmm^−/−) show polydactyly similar to talpid² and talpid³ mutants. Here we characterize the molecular profile of the hmm^−/− limb bud and identify the cellular mechanisms that cause its polydactyly. The hmm^−/− limb bud shows a severe lack of sonic hedgehog (SHH) signaling, and the autopod has 4 to 11 unidentifiable digits with syn-, poly-, and brachydactyly. The Zone of Polarizing Activity (ZPA) of the hmm^−/− limb bud does not show polarizing activity regardless of the presence of SHH protein, indicating that either the secretion pathway of SHH is defective or the SHH protein is dysfunctional. Furthermore, mesenchymal cells in the hmm^−/− limb bud do not respond to ZPA transplanted from the normal limb bud, suggesting that signal transduction downstream of SHH is also defective. Since primary cilia are present in the hmm^−/− limb bud, the causal gene must be different from talpid² and talpid³. In the hmm^−/− limb bud, a high amount of GLI3A protein is expressed and GLI3 protein is localized to the nucleus. Our results suggest that the regulatory mechanism of GLI3 is disorganized in the hmm^−/− limb bud.

An ELISA for quantifying quail IgY and characterizing maternal IgY transfer to egg yolk in several quail strains

In avian species, maternal blood immunoglobulin Y (IgY) is transferred to the egg yolks of maturing oocytes, but the mechanism underlying this transfer is unknown. To gain insight into the mechanism of maternal IgY transfer in quail, we established an enzyme-linked immunosorbent assay (ELISA) for the quantitation of quail IgY. We characterized strain differences in blood and egg yolk IgY concentrations and exogenously injected IgY-Fc uptakes into egg yolks. A specific rabbit polyclonal antibody to quail IgY was raised for the ELISA. Blood and egg yolk IgY concentrations were determined in six quail strains (one inbred strain, L; four closed population strains, AWE, DB, PS, WE; one commercial strain, Commercial). The birds were also injected with digoxigenin-labeled quail IgY-Fc, and its uptakes into laid eggs were compared. The strain difference in blood and egg yolk IgY concentrations was at most 2.5-fold, between PS and AWE. The rank order of IgY concentrations was AWE, Commercial, DB, L≥WE≥PS. A significant positive correlation (|R|=0.786) between individual blood IgY and egg yolk IgY and the concentrated egg yolk IgY (1.5-2-fold) against blood IgY was observed. Interestingly, there was a significant inverse correlation (|R|=0.452) between injected IgY-Fc uptakes and the blood IgY concentration, implying competition of the injected IgY-Fc and blood IgY in the process of IgY uptake into egg yolks. In conclusion, we successfully determined blood and egg yolk IgY concentrations in various quail strains by a quail IgY-specific ELISA. The concentrated egg yolk IgY against the blood IgY and the inverse relationship of exogenous IgY-Fc uptake against the blood IgY supports the existence of a selective IgY transport mechanism in avian maturing oocytes.

Chromosome size-correlated and chromosome size-uncorrelated homogenization of centromeric repetitive sequences in New World quails

Many families of centromeric repetitive DNA sequences isolated from Struthioniformes, Galliformes, Falconiformes, and Passeriformes are localized primarily to microchromosomes. However, it is unclear whether chromosome size-correlated homogenization is a common characteristic of centromeric repetitive sequences in Aves. New World and Old World quails have the typical avian karyotype comprising chromosomes of two distinct sizes, and C-positive heterochromatin is distributed in centromeric regions of most autosomes and the whole W chromosome. We isolated six types of centromeric repetitive sequences from three New World quail species (Colinus virginianus, CVI; Callipepla californica, CCA; and Callipepla squamata, CSQ; Odontophoridae) and one Old World quail species (Alectoris chukar, ACH; Phasianidae), and characterized the sequences by nucleotide sequencing, chromosome in situ hybridization, and filter hybridization. The 385-bp CVI-MspI, 591-bp CCA-BamHI, 582-bp CSQ-BamHI, and 366-bp ACH-Sau3AI fragments exhibited tandem arrays of the monomer unit, and the 224-bp CVI-HaeIII and 135-bp CCA-HaeIII fragments were composed of minisatellite-like and microsatellite-like repeats, respectively. ACH-Sau3AI was a homolog of the chicken nuclear membrane repeat sequence, whose homologs are common in Phasianidae. CVI-MspI, CCA-BamHI, and CSQ-BamHI showed high homology and were specific to the Odontophoridae. CVI-MspI was localized to microchromosomes, whereas CVI-HaeIII, CCA-BamHI, and CSQ-BamHI were mapped to almost all chromosomes. CCA-HaeIII was localized to five pairs of macrochromosomes and most microchromosomes. ACH-Sau3AI was distributed in three pairs of macrochromosomes and all microchromosomes. Centromeric repetitive sequences may be homogenized in chromosome size-correlated and -uncorrelated manners in New World quails, although there may be a mechanism that causes homogenization of centromeric repetitive sequences primarily between microchromosomes, which is commonly observed in phasianid birds.

Comparison of microsatellite variations between Red Junglefowl and a commercial chicken gene pool

It is assumed that Red Junglefowl (Gallus gallus) is one of the main ancestors of domestic chickens (Gallus gallus domesticus). Differences in microsatellite polymorphisms between Red Junglefowl and modern commercial chickens, which are used for egg and meat production, have not been fully reported. A total of 361 individuals from 1 Red Junglefowl population that has been maintained as a closed flock, 5 final cross-bred commercial layer populations (white-, tinted-, and brown-egg layers), and 2 final cross-bred commercial broiler populations were genotyped for 40 autosomal microsatellite loci. We compared microsatellite variations in Red Junglefowl with those in a commercial chicken gene pool. The contribution of each population to the genetic diversity was also estimated based on the molecular coancestry. In total, 302 distinct alleles were detected in 1 Red Junglefowl and 7 commercial chicken populations, of which 31 alleles (10.3%) were unique to Red Junglefowl, most of which occurred at a high frequency. The genetic differentiation between Red Junglefowl and commercial chickens (pairwise FST) ranged from 0.32 to 0.47. According to the neighbor-joining tree based on the modified Cavalli-Sforza chord distances and the Bayesian clustering analysis, Red Junglefowl was genetically distant from the commercial chicken gene pool tested. In all of the populations analyzed, Red Junglefowl made the highest contribution to genetic diversity. These results suggest that Red Junglefowl has a distinct distribution of microsatellite alleles and that there is a high level of genetic divergence between Red Junglefowl and commercial chickens.

Endothelin receptor B2 (EDNRB2) is responsible for the tyrosinase-independent recessive white (mo(w) ) and mottled (mo) plumage phenotypes in the chicken

A mutation that confers white plumage with black eyes was identified in the Minohiki breed of Japanese native chicken (Gallus gallus domesticus). The white plumage, with a few partially pigmented feathers, was not associated with the tyrosinase gene, and displayed an autosomal recessive mode of inheritance against the pigmented phenotype. All F1 offspring derived from crosses with mottled chickens (mo/mo), which show characteristic pigmented feathers with white tips, had plumage with a mottled-like pattern. This result indicates that the white plumage mutation is a novel allele at the mo locus; we propose the gene symbol mo(w) for this mutant allele. Furthermore, the F1 hybrid between the mo(w) /mo(w) chicken and the panda (s/s) mutant of Japanese quail (Coturnix japonica), whose causative gene is the endothelin receptor B2 (EDNRB2) gene, showed a mo(w)/mo(w) chicken-like plumage, suggesting the possibility that the mutations in parental species are alleles of the same gene, EDNRB2. Nucleotide sequencing of the entire coding region of EDNRB2 revealed a non-synonymous G1008T substitution, which causes Cys244Phe amino acid substitution in exon 5 (which is part of the extracellular loop between the putative fourth and fifth transmembrane domains of EDNRB2) in the mutant chicken. This Cys244Phe mutation was also present in individuals of four Japanese breeds with white plumage. We also identified a non-synonymous substitution leading to Arg332His substitution that was responsible for the mottled (mo/mo) plumage phenotype. These results suggest that the EDN3 (endothelin 3)-EDNRB2 signaling is essential for normal pigmentation in birds, and that the mutations of EDNRB2 may cause defective binding of the protein with endothelins, which interferes with melanocyte differentiation, proliferation, and migration.

Genetic characterization and conservation priorities of chicken lines

Molecular markers are a useful tool for evaluating genetic diversity of chicken genetic resources. Seven chicken lines derived from the Plymouth Rock breed were genotyped using 40 microsatellite markers to quantify genetic differentiation and assess conservation priorities for the lines. Genetic differentiation between pairs of the lines (pairwise FST) ranged from 0.201 to 0.422. A neighbor-joining tree of individuals, based on the proportion of shared alleles, formed clearly defined clusters corresponding to the origins of the lines. In Bayesian model-based clustering, most individuals were clearly assigned to single clusters according to line origin and showed no admixture. These results indicated that a substantial degree of genetic differentiation exists among the lines. To decide priorities for conservation, the contribution of each line to the genetic diversity was estimated. The result indicated that a loss of 4 of the 7 lines would lead to a loss from 1.14 to 3.44% of total genetic diversity. The most preferred line for conservation purposes was identified based on multilocus microsatellite analysis. Our results confirmed that characterization by means of molecular markers is helpful for establishing a plan for conservation of chicken genetic resources.

A genetically female brain is required for a regular reproductive cycle in chicken brain chimeras

Sexual differentiation leads to structural and behavioural differences between males and females. Here we investigate the intrinsic sex identity of the brain by constructing chicken chimeras in which the brain primordium is switched between male and female identities before gonadal development. We find that the female chimeras with male brains display delayed sexual maturation and irregular oviposition cycles, although their behaviour, plasma concentrations of sex steroids and luteinizing hormone levels are normal. The male chimeras with female brains show phenotypes similar to typical cocks. In the perinatal period, oestrogen concentrations in the genetically male brain are higher than those in the genetically female brain. Our study demonstrates that male brain cells retain male sex identity and do not differentiate into female cells to drive the normal oestrous cycle, even when situated in the female hormonal milieu. This is clear evidence for a sex-specific feature that develops independent of gonadal steroids.

Mapping quantitative trait loci for egg production traits in an F2 intercross of Oh-Shamo and White Leghorn chickens

We performed quantitative trait locus (QTL) analyses for egg production traits, including age at first egg (AFE) and egg production rates (EPR) measured every 4 weeks from 22 to 62 weeks of hen age, in a population of 421 F(2) hens derived from an intercross between the Oh-Shamo (Japanese Large Game) and White Leghorn breeds of chickens. Simple interval mapping revealed a main-effect QTL for AFE on chromosome 1 and four main-effect QTL for EPR on chromosomes 1 and 11 (three on chromosome 1 and one on chromosome 11) at the genome-wide 5% levels. Among the three EPR QTL on chromosome 1, two were identified at the early stage of egg laying (26-34 weeks of hen age) and the remaining one was discovered at the late stage (54-58 weeks). The alleles at the two EPR QTL derived from the Oh-Shamo breed unexpectedly increased the trait values, irrespective of the Oh-Shamo being inferior to the White Leghorn in the trait. This suggests that the Oh-Shamo, one of the indigenous Japanese breeds, is an untapped resource that is important for further improvement of current elite commercial laying chickens. In addition, six epistatic QTL were identified on chromosomes 2, 4, 7, 8, 17 and 19, where none of the above main-effect QTL were located. This is the first example of detection of epistatic QTL affecting egg production traits. The main and epistatic QTL identified accounted for 4-8% of the phenotypic variance. The total contribution of all QTL detected for each trait to the phenotypic and genetic variances ranged from 4.1% to 16.9% and from 11.5% to 58.5%, respectively.

Genetic differentiation among White Leghorn lines: application of individual-based clustering approaches

Genetic differentiations among White Leghorn lines were quantified based on allele frequencies of 40 microsatellite loci. In the survey among 7 lines, a considerable degree of differentiation was estimated between each pair of lines; genetic differentiation index (pairwise F(ST)) ranged from 0.0706 to 0.2590. Furthermore, 2 genetic clustering analyses of individuals, a neighbor-joining approach based on interindividual distances and the Bayesian procedure, which can assign individuals to the origins of their lines based on information on multilocus genotypes, were applied to a pairwise comparison of line differentiation. In the clustering approaches between the lowest differentiated line pair (pairwise F(ST) = 0.0706), individuals from 2 different line origins could not be separated into 2 distinct clusters, which indicates that the genetic boundary of these lines is ambiguous. On the other hand, between the highest differentiated pair (pairwise F(ST) = 0.2590), all individuals could be strictly clustered into 2 distinct groups, consistent with the origins of their lines. In the clustering based on interindividual distances, firm separations of individuals were observed in only relatively highly differentiated pairs of lines. Furthermore, in the Bayesian procedure, even in pairs with a relatively low differentiation, individuals from 2 lines formed 2 distinct clusters according to their origins. The results of the present study suggest that chicken lines possess considerable genetic differentiation despite their common breed origin. These clustering approaches at the individual level may be useful for the genetic identification and characterization of poultry stocks.

Molecular characterization reveals genetic uniformity in experimental chicken resources

The objective of the present study was to conduct the genetic characterization of nine experimental chicken lines based on multilocus microsatellite analysis. Commercial chicken lines were also analyzed in order to compare their levels of genetic uniformity with those of the experimental lines. In six experimental lines, more than 80% of genotyped loci showed fixed allele for all individuals in each line, whereas only 17.5% of genotyped loci were fixed in commercial lines, at the maximum. One of experimental lines (GSN/1) was categorized as a highly inbred line on the basis of all individuals having the same, single allele at every microsatellite locus. Genetic information obtained from the present study should be helpful for the utilization and management of experimental chicken resources.

High accuracy of genetic discrimination among chicken lines obtained through an individual assignment test

In the current study, we carried out assignment tests applying the Bayesian and distance-based methods, using 20 microsatellite genotypes in four chicken lines. The Bayesian method showed slightly higher performance of assignment than the distance-based method. In the assignment using the Bayesian method, >or=90% accuracy of assignment was attained by using only two of the most heterozygous markers, whereas in the case of the least heterozygous markers, six were needed to reach the same level of accuracy. In the assignment of the most closely related line pair (F(ST) = 0.1736), at least 12 markers selected by random ordering and at least 15 individuals per line were needed to stably obtain high accuracy of assignment (>or=97%), whereas using only six random markers achieved 97-100% of accuracy between the two most distinct lines (F(ST) = 0.3651) without reference to the sample size per line.

Identification of quantitative trait loci affecting shank length, body weight and carcass weight from the Japanese cockfighting chicken breed, Oh-Shamo (Japanese Large Game)

We performed a quantitative trait locus (QTL) analysis to map QTLs controlling shank length, body weight, and carcass weight in a resource family of 245 F(2) birds developed from a cross of the large-sized, native, Japanese cockfighting breed, Oh-Shamo (Japanese Large Game), and the White Leghorn breed of chickens. Interval mapping revealed three significant QTLs for shank length on chromosomes 1, 4 and 24 at the experiment-wise 5% level, and a suggestive shank length QTL on chromosome 27 at the experiment-wise 10% level. For body weight two QTLs, one significant and the other suggestive, were identified on chromosomes 4 and 24, respectively. As expected, QTLs for carcass weight, which was highly correlated with body weight (r = 0.95), were detected at the same chromosomal locations as the detected body weight QTLs. Interestingly, the chromosomal locations containing these body weight and carcass weight QTLs coincided with those of two of the four shank length QTLs detected. No QTL with an epistatic interaction effect was discovered for any trait. The total contribution of all detected QTLs to genetic variance was 98.4%, 27.0% and 25.9% for shank length, body weight and carcass weight, respectively, indicating that most shank length QTLs have been identified but many body weight and carcass weight QTLs have been overlooked by the present analysis because of a low coverage rate of the 88 microsatellite markers used here (approximately 46% of the whole genome).

Microsatellite Marker Analysis for the Genetic Relationships Among Japanese Long-Tailed Chicken Breeds

The present study was conducted to evaluate the genetic diversity and relationships of 9 native Japanese long-tailed chicken breeds (Shoukoku, Koeyoshi, Kurokashiwa, Minohiki, Ohiki, Onagadori, Satsumadori, Toumaru, and Toutenkou) together with 2 commercial breeds (White Leghorn and White Plymouth Rock), using 40 polymorphic microsatellite markers covering 23 linkage groups. The 8 breeds mentioned, except for Shoukoku and 2 commercial breeds, were believed to be descendants derived from crossings of the ancestor of Shoukoku and some other breeds. Three to 14 alleles per locus were detected across all the breeds. The mean number of alleles per locus, the mean unbiased expected heterozygosity, and the mean polymorphic information content ranged from 2.60 (Minohiki) to 4.07 (Shoukoku), from 0.293 (Koeyoshi) to 0.545 (Satsumadori), and from 0.250 (Koeyoshi) to 0.478 (Satsumadori), respectively. The mean fixation coefficient of subpopulation within the total population of 9 Japanese long-tailed breeds showed that approximately 38% of the genetic variation was caused by breed differences and 62% was due to differences among individuals. Toumaru had the largest number of breed-specific alleles with relatively high (>20%) frequency. In the phylogenetic tree of 11 breeds constructed by the neighbor-joining method from modified Cavalli-Sforza chord genetic distance measure, White Leghorn and White Plymouth Rock clustered together apart from the Japanese breeds. Among the Japanese long-tailed breeds, Toumaru, Kurokashiwa, and Koeyoshi showed relatively far distance from the other breeds. The Ohiki, Onagadori, Shoukoku, and Toutenkou were grouped into the same branch. Minohiki and Satsumadori were also clustered together. Kurokashiwa was not genetically close to Shoukoku, differing from a traditional hypothsis. It was confirmed in the present study that the microsatellite is a suitable tool to evaluate genetic diversity and relationships in chicken breeds.

A novel family of repetitive DNA sequences amplified site-specifically on the W chromosomes in Neognathous birds

A novel family of repetitive DNA sequences was molecularly cloned from ApaI-digested genomic DNA of two Galliformes species, Japanese quail (Coturnix japonica) and guinea fowl (Numida meleagris), and characterized by chromosome in-situ hybridization and filter hybridization. Both the repeated sequence elements produced intensely painted signals on the W chromosomes, whereas they weakly hybridized to whole chromosomal regions as interspersed-type repetitive sequences. The repeated elements of the two species had high similarity of nucleotide sequences, and cross-hybridized to chromosomes of two other Galliformes species, chicken (Gallus gallus) and blue-breasted quail (Coturnix chinensis). The nucleotide sequences were conserved in three other orders of Neognathous birds, the Strigiformes, Gruiformes and Falconiformes, but not in Palaeognathous birds, the Struthioniformes and Tinamiformes, indicating that the repeated sequence elements were amplified on the W chromosomes in the lineage of Neognathous birds after the common ancestor diverged into the Palaeognathae and Neognathae. They are components of the W heterochromatin in Neognathous birds, and a good molecular cytogenetic marker for estimating the phylogenetic relationships and for clarifying the origin of the sex chromosome heterochromatin and the process of sex chromosome differentiation in birds.

A chicken linkage map based on microsatellite markers genotyped on a Japanese Large Game and White Leghorn cross

A detailed linkage map is necessary for efficient detection of quantitative trait loci (QTL) in chicken resource populations. In this study, microsatellite markers isolated from a (CA)n-enriched library (designated as ABR Markers) were mapped using a population developed from a cross between Japanese Game and White Leghorn chickens. In total, 296 markers including 193 ABR, 43 MCW, 31 ADL, 22 LEI, 3 HUJ, 2 GCT, 1 UMA and 1 ROS were mapped by linkage to chicken chromosomes 1-14, 17-21, 23, 24, 26-28 and Z. In addition, five markers were assigned to the map based on the chicken draft genomic sequence, bringing the total number of markers on the map to 301. The resulting linkage map will contribute to QTL mapping in chicken.

Evolution of the vertebrate DNMT3 gene family: a possible link between existence of DNMT3L and genomic imprinting

DNA methylation plays an essential role in genomic imprinting observed in eutherian mammals and marsupials. In mouse, one of the two de novo DNA methyltransferases, Dnmt3a, and a related protein, Dnmt3L have been shown to be essential for imprint establishment in the parental germline. To gain insights into the evolution of imprinting mechanisms, we have identified and characterized the DNMT3 family genes in other vertebrate species. We cloned cDNAs for chicken DNMT3A and DNMT3B, whose putative protein products shared 81.5% and 48.6% amino acid sequence identity with their mouse orthologues. Using computer-assisted database searches, we also identified DNMT3A and DNMT3B orthologues in fish (fugu and zebrafish) and marsupials (opossum). We found that, while opossums had an orthologue for DNMT3L, chickens and fish did not have this gene. Thus, unlike the other DNMT3 members, DNMT3L was restricted to the species in which imprinting occurs. The acquisition of DNMT3L by a common ancestor of eutherians and marsupials might have been closely related to the evolution of imprinting.

A nucleotide substitution responsible for the tawny coat color mutation carried by the MSKR inbred strain of mice

"Tawny" is an autosomal recessive coat color mutation found in a wild population of Mus musculus molossinus. The inbred strain MSKR carries the mutation. The causative gene Mc1r(taw) of the tawny phenotype is the second recessive allele at the melanocortin 1 receptor locus and is dominant to the first recessive allele, "recessive yellow" (Mc1r(e)). The Mc1r(taw) gene has six nucleotide substitutions, and its forecasted transcript has three amino acid substitutions (i.e., V101A, V216A, W252C). Though the nucleotide substitutions leading to V101A and V216A exist in various mouse strains, the nucleotide substitution leading to W252C exists in only tawny-colored mice. Thus this substitution is considered to be responsible for the expression of the tawny coat color. The frequency of the allele having this nucleotide substitution was 9.21% in the wild M. m. molossinus population inhabiting Sakai City, Osaka Prefecture, Japan, where the ancestral mice of the MSKR strain were captured.

Culture System for Embryos of Blue-Breasted Quail from the Blastoderm Stage to Hatching

The blue-breasted quail (Coturnix chinensis), the smallest species in the order Galliforms, is a candidate model animal for avian developmental engineering because it is precocious and prolific. This species requires 17 days to hatch and 8 to 9 weeks to mature to an adult body weight of about 50 g, whereas the Japanese quail (Coturnix japonica) requires 16 days to hatch and 6 to 8 weeks to mature to an adult body weight of 100 to 150 g. The early embryo is the most challenging embryonic stage in terms of culture and manipulation for avian biotechnology. We have evaluated various conditions for the culture of blue-breasted quail embryos from the blastoderm stage to hatching. A hatchability rate of 26% (10/39) is among the best of the various culture conditions examined in the present study and the embryo culture system should facilitate advances in avian biotechnology.

Structural and functional analysis of a 0.5-Mb chicken region orthologous to the imprinted mammalian Ascl2/Mash2-Igf2-H19 region

Previous studies revealed that Igf2 and Mpr/Igf2r are imprinted in eutherian mammals and marsupials but not in monotremes or birds. Igf2 lies in a large imprinted cluster in eutherians, and its imprinting is regulated by long-range mechanisms. As a step to understand how the imprinted cluster evolved, we have determined a 490-kb chicken sequence containing the orthologs of mammalian Ascl2/Mash2, Ins2 and Igf2. We found that most of the genes in this region are conserved between chickens and mammals, maintaining the same transcriptional polarities and exon-intron structures. However, H19, an imprinted noncoding transcript, was absent from the chicken sequence. Chicken ASCL2/CASH4 and INS, the orthologs of the imprinted mammalian genes, showed biallelic expression, further supporting the notion that imprinting evolved after the divergence of mammals and birds. The H19 imprinting center and many of the local regulatory elements identified in mammals were not found in chickens. Also, a large segment of tandem repeats and retroelements identified between the two imprinted subdomains in mice was not found in chickens. Our findings show that the imprinted genes were clustered before the emergence of imprinting and that the elements associated with imprinting probably evolved after the divergence of mammals and birds.

Karyotypic evolution in the Galliformes: an examination of the process of karyotypic evolution by comparison of the molecular cytogenetic findings with the molecular phylogeny

To define the process of karyotypic evolution in the Galliformes on a molecular basis, we conducted genome-wide comparative chromosome painting for eight species, i.e. silver pheasant (Lophura nycthemera), Lady Amherst's pheasant (Chrysolophus amherstiae), ring-necked pheasant (Phasianus colchicus), turkey (Meleagris gallopavo), Western capercaillie (Tetrao urogallus), Chinese bamboo-partridge (Bambusicola thoracica) and common peafowl (Pavo cristatus) of the Phasianidae, and plain chachalaca (Ortalis vetula) of the Cracidae, with chicken DNA probes of chromosomes 1-9 and Z. Including our previous data from five other species, chicken (Gallus gallus), Japanese quail (Coturnix japonica) and blue-breasted quail (Coturnix chinensis) of the Phasianidae, guinea fowl (Numida meleagris) of the Numididae and California quail (Callipepla californica) of the Odontophoridae, we represented the evolutionary changes of karyotypes in the 13 species of the Galliformes. In addition, we compared the cytogenetic data with the molecular phylogeny of the 13 species constructed with the nucleotide sequences of the mitochondrial cytochrome b gene, and discussed the process of karyotypic evolution in the Galliformes. Comparative chromosome painting confirmed the previous data on chromosome rearrangements obtained by G-banding analysis, and identified several novel chromosome rearrangements. The process of the evolutionary changes of macrochromosomes in the 13 species was in good accordance with the molecular phylogeny, and the ancestral karyotype of the Galliformes is represented.

A comparative karyological study of the blue-breasted quail (Coturnix chinensis, Phasianidae) and California quail (Callipepla californica, Odontophoridae)

We conducted comparative chromosome painting and chromosome mapping with chicken DNA probes against the blue-breasted quail (Coturnix chinensis, CCH) and California quail (Callipepla californica, CCA), which are classified into the Old World quail and the New World quail, respectively. Each chicken probe of chromosomes 1-9 and Z painted a pair of chromosomes in the blue-breasted quail. In California quail, chicken chromosome 2 probe painted chromosomes 3 and 6, and chicken chromosome 4 probe painted chromosomes 4 and a pair of microchromosomes. Comparison of the cytogenetic maps of the two quail species with those of chicken and Japanese quail revealed that there are several intrachromosomal rearrangements, pericentric and/or paracentric inversions, in chromosomes 1, 2 and 4 between chicken and the Old World quail. In addition, a pericentric inversion was found in chromosome 8 between chicken and the three quail species. Ordering of the Z-linked DNA clones revealed the presence of multiple rearrangements in the Z chromosomes of the three quail species. Comparing these results with the molecular phylogeny of Galliformes species, it was also cytogenetically supported that the New World quail is classified into a different clade from the lineage containing chicken and the Old World quail.

Biallelic expression of Z-linked genes in male chickens

In birds, females are heterogametic (ZW), while males are homogametic (ZZ). It has been proposed that there is no dosage compensation for the expression of Z-linked genes in birds. In order to examine if the genes are inactivated on one of the two Z chromosomes, we analyzed the allelic expression of the B4GALT1 and CHD-Z genes on Z chromosomes in male chickens. One base substitution was detected among 15 chicken breeds and lines examined for each gene, and cross mating was made between the breeds or lines with polymorphism. cDNAs were synthesized from cultured cell colonies each derived from a single cell of an F1 male embryo. The allelic expression of the B4GALT1 gene was examined by restriction fragment length polymorphism analysis of the PCR products digested with RSAI, and that of the CHD-Z gene by the single nucleotide primer extension (SNuPE) method. Both of the genes displayed biallelic expression, suggesting that these Z-linked genes were not subject to inactivation in male chickens. Comparison between expression levels in males and females by real-time quantitative PCR suggested that expression was compensated for the CHD-Z gene but not for the B4GALT1 gene.

Molecular cloning and characterization of novel centromeric repetitive DNA sequences in the blue-breasted quail (Coturnix chinensis, Galliformes)

A new family of centromeric highly repetitive DNA sequences was isolated from EcoRI-digested genomic DNA of the blue-breasted quail (Coturnix chinensis, Galliformes), and characterized by filter hybridization and chromosome in situ hybridization. The repeated elements were divided into two types by nucleotide length and chromosomal distribution; the 578-bp element predominantly localized to microchromosomes and the 1,524-bp element localized to chromosomes 1 and 2. The 578-bp element represented tandem arrays and did not hybridize to genomic DNAs of other Galliformes species, chicken (Gallus gallus), Japanese quail (Coturnix japonica) and guinea fowl (Numida meleagris). On the other hand, the 1,524-bp element was not organized in tandem arrays, and did hybridize to the genomic DNAs of three other Galliformes species, suggesting that the 1,524-bp element is highly conserved in the Galliformes. The 578-bp element was composed of basic 20-bp internal repeats, and the consensus nucleotide sequence of the internal repeats had homologies to the 41-42 bp CNM repeat and the XHOI family repeat of chicken. Our data suggest that the microchromosome-specific highly repetitive sequences of the blue-breasted quail and chicken were derived from a common ancestral sequence, and that they are one of the major and essential components of chromosomal heterochromatin in Galliformes species.