Comparative FISH mapping on Z chromosomes of chicken and Japanese quail

Unusual chromosome numbers and polyploidy in invasive fire ant populations

Fire ants (Solenopsis invicta Buren in J Ga Entomol Soc 7:1-26, 1972), an invasive alien ant species, first spread from South America to the United States in the 1930s, the southern part of the United States by the end of the twentieth century, Oceania, Taiwan, and China in the twenty-first century, and finally to Japan and South Korea in 2017. As these ants have significant negative economic, human health, and environmental impacts, the purpose of this research was to accumulate cytogenetic information regarding fire ants and provide basic data for developing management strategies for their control. Fire ants were collected from invasive populations from Taiwan, Florida (USA), and Buenos Aires (Argentina), and a native population from Puerto Iguazu (Argentina), their point of origination, and analyzed with regard to chromosome number, morphology, and polyploidy, silver-stained nucleolar organizer regions (Ag-NORs), and 18S rDNA and telomere fluorescence in situ hybridization (FISH). The results showed that (1) fire ants from invaded populations differed in chromosome morphology compared to those from native populations; (2) the Florida and Taiwanese fire ant populations evinced greater variability in chromosome numbers and polyploidy variations; (3) the Taiwanese population exhibited significantly increased Ag-NOR signals in interphase cells, with signal number significantly positively correlating with distance from native populations; and (4) substantial diversity of signals was also apparent following 18S rDNA and telomere FISH analyses. Variation in these characteristics were hypothesized to be due to (1) the effect of hybridizations and interbreeding between closely related species or genetically distant populations, and (2) the potential effect of large amounts of insecticides sprayed for pest control.

Banding cytogenetics of chimeric hybrids Coturnixcoturnix × Coturnixjaponica and comparative analysis with the domestic fowl

The Common quail Coturnixcoturnix Linnaeus, 1758 is a wild migratory bird which is distributed in Eurasia and North Africa, everywhere with an accelerating decline in population size. This species is protected by the Bonn and Berne conventions (1979) and by annex II/1 of the Birds Directive (2009). In Algeria, its breeding took place at the hunting centre in the west of the country. Breeding errors caused uncontrolled crosses between the Common quail and Japanese quail Coturnixjaponica Temminck & Schlegel, 1849. In order to help to preserve the natural genetic heritage of the Common quail and to lift the ambiguity among the populations of quail raised in Algeria, it seemed essential to begin to describe the chromosomes of this species in the country since no cytogenetic study has been reported to date. Fibroblast cultures from embryo and adult animal were initiated. Double synchronization with excess thymidine allowed us to obtain high resolution chromosomes blocked at prometaphase stage. The karyotype and the idiogram in GTG morphological banding (G-bands obtained with trypsin and Giemsa) corresponding to larger chromosomes 1-12 and ZW pair were thus established. The diploid set of chromosomes was estimated as 2N=78. Cytogenetic analysis of expected hybrid animals revealed the presence of a genetic introgression and cellular chimerism. This technique is effective in distinguishing the two quail taxa. Furthermore, the comparative chromosomal analysis of the two quails and domestic chicken Gallusgallusdomesticus Linnaeus, 1758 has been conducted. Differences in morphology and/or GTG band motifs were observed on 1, 2, 4, 7, 8 and W chromosomes. Neocentromere occurrence was suggested for Common quail chromosome 1 and Chicken chromosomes 4 and W. Double pericentric inversion was observed on the Common quail chromosome 2 while pericentric inversion hypothesis was proposed for Chicken chromosome 8. A deletion on the short arm of the Common quail chromosome 7 was also found. These results suggest that Common quail would be a chromosomally intermediate species between Chicken and Japanese quail. The appearance of only a few intrachromosomal rearrangements that occurred during evolution suggests that the organization of the genome is highly conserved between these three galliform species.

FISH mapping of 57 BAC clones reveals strong conservation of synteny between Galliformes and Anseriformes

Karyotypes of chicken (Gallus gallus domesticus; 2n = 78) and mallard duck (Anas platyrhynchos; 2n = 80) share the typical organization of avian karyotypes including a few macrochromosome pairs, numerous indistinguishable microchromosomes, and Z and W sex chromosomes. Previous banding studies revealed great similarities between chickens and ducks, but it was not possible to use comparative banding for the microchromosomes. In order to establish precise chromosome correspondences between these two species, particularly for microchromosomes, we hybridized 57 BAC clones previously assigned to the chicken genome to duck metaphase spreads. Although most of the clones showed similar localizations, we found a few intrachromosomal rearrangements of the macrochromosomes and an additional microchromosome pair in ducks. BAC clones specific for chicken microchromosomes were localized to separate duck microchromosomes and clones mapping to the same chicken microchromosome hybridized to the same duck microchromosome, demonstrating a high conservation of synteny. These results demonstrate that the evolution of karyotypes in avian species is the result of fusion and/or fission processes and not translocations.

Comparison of the chicken and zebra finch Z chromosomes shows evolutionary rearrangements

Using fluorescent in-situ hybridization (FISH) of zebra finch (Taeniopygia guttata) bacterial artificial chromosome (BAC) clones, we determined the chromosomal localizations of 14 zebra finch genes that are Z-linked in chickens: ATP5A1, CHD1, NR2F1, DMRT1, PAM, GHR, HSD17B4, NIPBL, ACO1, HINT1, SMAD2, SPIN, NTRK2 and UBE2R2. All 14 genes also map to the zebra finch Z chromosome, indicating substantial conservation of gene content on the Z chromosome in the two avian lineages. However, the physical order of these genes on the zebra finch Z chromosome differed from that of the chicken, in a pattern that would have required several inversions since the two lineages diverged. Eight of 14 zebra finch BAC DNA showed cross-hybridization to the W chromosome, usually to the entire W chromosome, suggesting that repetitive sequences are shared by the W and Z chromosomes. These repetitive sequences likely evolved in the finch lineage after it diverged from the Galliform lineage.

Molecular cytogenetic definition of the chicken genome: the first complete avian karyotype

Chicken genome mapping is important for a range of scientific disciplines. The ability to distinguish chromosomes of the chicken and other birds is thus a priority. Here we describe the molecular cytogenetic characterization of each chicken chromosome using chromosome painting and mapping of individual clones by FISH. Where possible, we have assigned the chromosomes to known linkage groups. We propose, on the basis of size, that the NOR chromosome is approximately the size of chromosome 22; however, we suggest that its original assignment of 16 should be retained. We also suggest a definitive chromosome classification system and propose that the probes developed here will find wide utility in the fields of developmental biology, DT40 studies, agriculture, vertebrate genome organization, and comparative mapping of avian species.

Genomic sequence of a 320-kb segment of the Z chromosome of Bombyx mori containing a kettin ortholog

The sex chromosome constitution of the silkworm, Bombyx mori, is ZW in the female and ZZ in the male. Very little molecular information is available about the Z chromosome in Lepidoptera, although the topic is interesting because of the absence of gene dosage compensation in this chromosome. We constructed a 320-kb BAC contig around the Bmkettin gene on the Z chromosome in Bombyx and determined its nucleotide sequence by the shotgun method. We found 13 novel protein-coding sequences in addition to Bmkettin. All the transposable elements detected in the region were truncated, and no LTR retrotransposons were found, in stark contrast to the situation on the W chromosome. In this 320-kb region, four genes for muscle proteins (Bmkettin, Bmtitin1, Bmtitin2, and Bmprojectin) are clustered, together with another gene (Bmmiple) on the Z chromosome in B. mori; their orthologs are also closely linked on chromosome 3 in Drosophila, suggesting a partial synteny. Real-time RT-PCR experiments demonstrated that transcripts of 13 genes of the 14 Z-linked genes found accumulated in larger amounts in males than in female moths, indicating the absence of gene dosage compensation. The implications of these findings for the evolution and function of the Z chromosome in Lepidoptera are discussed.

Conservation of avian Z chromosomes as revealed by comparative mapping of the Z-linked aldolase B gene

A chicken Z-linked BAC probe containing the aldolase B gene was used for fluorescence in-situ hybridization (FISH) mapping in four different avian species. The biotinylated BAC clone showed distinct unique hybridization sites on the structurally different Z chromosomes. This result, together with previous data, lends credence to the notion that, despite undergoing structural rearrangements, the gene content of the avian Z chromosome remained conserved during evolution. Our study also demonstrates the feasibility of using large genomic clones for comparative mapping of Z-linked genes in birds.

Chicken microsatellite primers are not efficient markers for Japanese quail

Domestic fowl or chicken (Gallus gallus) and Japanese quail (Coturnix japonica) belong to the family Phasianidae. The exchange of marker information between chicken and quail is an important step towards the construction of a high-resolution comparative genetic map in Phasianidae, which includes several poultry species of agricultural importance. We tested chicken microsatellite markers to see if they would be suitable as genetic linkage markers in Japanese quail. Twenty-six per cent (31/120) of chicken primers amplified individual loci in Japanese quail and 65% (20/31) of the amplified loci were found to be polymorphic. Eleven of the polymorphic loci were excluded as uninformative because of the lack of amplification in some individuals or high frequency of nonspecific amplification. The sequence information of the remaining nine loci revealed six of them to contain microsatellites that were nearly identical with those of the orthologous regions in chicken. For these six loci, allele frequencies were estimated in 50 unrelated quails. Although the very few chicken markers that do work well in quail could be used as anchor points for a comparative mapping, most chicken markers are not useful for studies in quail. Therefore, more effort should be committed to developing quail-specific markers rather than attempting to adapt chicken markers for work in quail.

Conserved synteny between the chicken Z sex chromosome and human chromosome 9 includes the male regulatory gene DMRT1: a comparative (re)view on avian sex determination

Sex-determination mechanisms in birds and mammals evolved independently for more than 300 million years. Unlike mammals, sex determination in birds operates through a ZZ/ZW sex chromosome system, in which the female is the heterogametic sex. However, the molecular mechanism remains to be elucidated. Comparative gene mapping revealed that several genes on human chromosome 9 (HSA 9) have homologs on the chicken Z chromosome (GGA Z), indicating the common ancestry of large parts of GGA Z and HSA 9. Based on chromosome homology maps, we isolated a Z-linked chicken ortholog of DMRT1, which has been implicated in XY sex reversal in humans. Its location on the avian Z and within the sex-reversal region on HSA 9p suggests that DMRT1 represents an ancestral dosage-sensitive gene for vertebrate sex-determination. Z dosage may be crucial for male sexual differentiation/determination in birds.