Contribution de la cytogénétique à l'étude de la fertilité de 2 lignées de poules pondeuses sélectionnées sur la consommation alimentaire résiduelle

Deux lignées de poules pondeuses ont été sélectionnées sur la consommation alimentaire résiduelle (+ R à consommation élevée, R- à faible consommation). Une détérioration des taux de fertilité et d’éclosion est observée dans la lignée R+. De nombreuses études réalisées sur les mammifères et les oiseaux ont montré l’association entre la mortalité embryonnaire et la présence d’anomalies chromosomiques. Dans le présent travail, des observations phénotypiques et des analyses cytogénétiques - limitées aux 10 premières paires de chromosomes observées et aux chromosomes sexuels, pour un total de 2n = 78 - ont été effectuées sur des embryons âgés de 48 ou de 16-18 h issus des 2 lignées R- et R+ aux générations 14 et 15. Des prélèvements de pulpes de plumes ont aussi permis de déterminer le caryotype de quelques adultes reproducteurs issus des 2 lignées. Le pourcentage d’oeufs clairs (non fécondés) est toujours significativement plus élevé en lignée R+. Les quelques cas d’anomalies chromosomiques mises en évidence dans les 2 lignées ne semblent pas être à l’origine de la baisse de fertilité de la lignée R+. Les reproducteurs adultes étudiés avaient tous des caryotypes normaux. L’explication de la baisse de fertilité en lignée R+ s’orienterait plutôt vers un problème de qualité des spermatozoïdes ou de leur conservation dans les voies génitales femelles dans la mesure ou l’étude cytogénétique n’a montré aucune anomalie de la méiose femelle ou de la multiplication des cellules embryonnaires. De plus les difficultés de reproduction ne sont pas concentrées dans certaines familles mais retrouvées dans toute la lignée.Two lines of brown egg layers have been divergently selected on residual food consumption (RFC). They differ markedly in their reproductive performance which deteriorates in the line selected on high values of RFC (R+ line). Several studies carried out in mammals and birds have shown a clear association between embryonic mortality and chromosomal abnormalities. In this study, fertile eggs were sampled from both lines at generations 14 and 15 after 48 or 16-18 h of incubation in order to observe the embryo development and determine the karyotype, on the first 10 pairs of chromosomes observed and sexual chromosomes, out of a total 2n = 78. Karyotypes were also prepared from feather pulps of adult breeders. The percentage of unfertilized eggs was always significantly higher in the R+ line. The few chromosomal abnormalities observed in both lines could not be responsible for the reduction in fertility in the R+ line. The adult karyotypes were normal. The lower fertility in the R+ line probably involves the quality of sperm cells or their conservation in the female genital tract, since cytogenetic analysis did not show any specific abnormality in female meiosis or in embryo cell multiplication. Furthermore, fertility problems were not clustered in some families but distributed over the entire line

The Crest Phenotype in Chicken Is Associated with Ectopic Expression of HOXC8 in Cranial Skin

The Crest phenotype is characterised by a tuft of elongated feathers atop the head. A similar phenotype is also seen in several wild bird species. Crest shows an autosomal incompletely dominant mode of inheritance and is associated with cerebral hernia. Here we show, using linkage analysis and genome-wide association, that Crest is located on the E22C19W28 linkage group and that it shows complete association to the HOXC-cluster on this chromosome. Expression analysis of tissues from Crested and non-crested chickens, representing 26 different breeds, revealed that HOXC8, but not HOXC12 or HOXC13, showed ectopic expression in cranial skin during embryonic development. We propose that Crest is caused by a cis-acting regulatory mutation underlying the ectopic expression of HOXC8. However, the identification of the causative mutation(s) has to await until a method becomes available for assembling this chromosomal region. Crest is unfortunately located in a genomic region that has so far defied all attempts to establish a contiguous sequence

Integrative mapping analysis of chicken microchromosome 16 organization

<p>Abstract</p> <p>Background</p> <p>The chicken karyotype is composed of 39 chromosome pairs, of which 9 still remain totally absent from the current genome sequence assembly, despite international efforts towards complete coverage. Some others are only very partially sequenced, amongst which microchromosome 16 (GGA16), particularly under-represented, with only 433 kb assembled for a full estimated size of 9 to 11 Mb. Besides the obvious need of full genome coverage with genetic markers for QTL (Quantitative Trait Loci) mapping and major genes identification studies, there is a major interest in the detailed study of this chromosome because it carries the two genetically independent <it>MHC </it>complexes <it>B </it>and <it>Y</it>. In addition, GGA16 carries the ribosomal RNA (<it>rRNA</it>) genes cluster, also known as the <it>NOR </it>(nucleolus organizer region). The purpose of the present study is to construct and present high resolution integrated maps of GGA16 to refine its organization and improve its coverage with genetic markers.</p> <p>Results</p> <p>We developed 79 STS (Sequence Tagged Site) markers to build a physical RH (radiation hybrid) map and 34 genetic markers to extend the genetic map of GGA16. We screened a BAC (Bacterial Artificial Chromosome) library with markers for the <it>MHC-B</it>, <it>MHC-Y </it>and <it>rRNA </it>complexes. Selected clones were used to perform high resolution FISH (Fluorescent <it>In Situ </it>Hybridization) mapping on giant meiotic lampbrush chromosomes, allowing meiotic mapping in addition to the confirmation of the order of the three clusters along the chromosome. A region with high recombination rates and containing PO41 repeated elements separates the two <it>MHC </it>complexes.</p> <p>Conclusions</p> <p>The three complementary mapping strategies used refine greatly our knowledge of chicken microchromosome 16 organisation. The characterisation of the recombination hotspots separating the two <it>MHC </it>complexes demonstrates the presence of PO41 repetitive sequences both in tandem and inverted orientation. However, this region still needs to be studied in more detail.</p

Distribution of HOX genes in the chicken genome reveals a new segment of conservation between human and chicken

Homeobox genes play an important role in the regulation of early embryonic development. They represent a family of evolutionarily highly conserved transcription factors. In this work, several genes that belong to the four HOX gene clusters are assigned by in situ hybridization to four distinct chicken chromosomes. The four gene clusters are mapped to 2p2.1 (HOXA), 3q3.1 (HOXB), 1q3.1 (HOXC) and 7q1.3 --> q1.4 (HOXD). We confirm partial homologies already detected by genetic mapping between chicken chromosomes 1, 2 and 7 and human chromosomes 12, 7 and 2 and we describe a new conserved segment between chicken chromosome 3 and human chromosome 17. These results represent the first data that confirm the physical linkage between chicken HOX genes and may improve our understanding of phylogenetic relationships and genome evolution. Copyright (C) 2001 S. Karger AG, Basel

The avian fli gene is specifically expressed during embryogenesis in a subset of neural crest cells giving rise to mesenchyme

The ets-family of transcription factors is involved in the development of endothelial and hematopoietic cells. Among these genes, fli was shown to be responsible for erythroblastomas and Ewing's sarcomas. Its involvement in Ewing's sarcoma, a putative neurectodermal tumor, as well as the in situ hybridization studies performed in mice and Xenopus suggested a role in neural crest development. We cloned quail iii cDNA in order to analyze in more detail its expression in neural crest cells, which have been extensively studied in avian species. Fli gene maps on chicken chromosome 1 to band q31-->q33. Two RNAs are transcribed, most likely arising from two different promoters. The analysis of its expression in neural crest cells reveals that it is expressed rather late, when the neural crest cells reach their target. Among the various lineages derived from the crest, it is restricted to the mesenchymal one. It is maintained at later stages in the cartilage of neural crest but also of mesodermal origin. In addition, iii is expressed in several mesoderm-derived cells: endothelial cells as well as intermediate and splanchnopleural mesoderm