Positional cloning of the PIS mutation in goats and its impact on understanding mammalian sex-differentiation

In goats, the PIS (polled intersex syndrome) mutation is responsible for both the absence of horns in males and females and sex-reversal affecting exclusively XX individuals. The mode of inheritance is dominant for the polled trait and recessive for sex-reversal. In XX PIS-/- mutants, the expression of testis-specific genes is observed very precociously during gonad development. Nevertheless, a delay of 4–5 days is observed in comparison with normal testis differentiation in XY males. By positional cloning, we demonstrate that the PIS mutation is an 11.7-kb regulatory-deletion affecting the expression of two genes, PISRT1 and FOXL2 which could act synergistically to promote ovarian differentiation. The transcriptional extinction of these two genes leads, very early, to testis-formation in XX homozygous PIS-/- mutants. According to their expression profiles and bibliographic data, we propose that FOXL2 may be an ovary-differentiating gene, and the non-coding RNA PISRT1, an anti-testis factor repressing SOX9, a key regulator of testis differentiation. Under this hypothesis, SRY, the testis-determining factor would inhibit these two genes in the gonads of XY males, to ensure testis differentiation

A repetitive probe for FISH analysis of bovine interphase nuclei

The purpose of this study was to generate repetitive DNA sequence probes for the analysis of interphase nuclei by fluorescent in situ hybridisation (FISH). Such probes are useful for the diagnosis of chromosomal abnormalities in bovine preimplanted embryos. Of the seven probes (E1A, E4A, Ba, H1A, W18, W22, W5) that were generated and partially sequenced, five corresponded to previously described Bos taurus repetitive DNA (E1A, E4A, Ba, W18, W5), one probe (W22) shared no homology with other DNA sequences and one (H1A) displayed a significant homology with Rattus norvegicus mRNA for secretin receptor transmembrane domain 3. Fluorescent in situ hybridisation was performed on metaphase bovine fibroblast cells and showed that five of the seven probes hybridised most centromeres (E1A, E4A, Ba, W18, W22), one labelled the arms of all chromosomes (W5) and the H1A probe was specific to three chromosomes (ch14, ch20, and ch25). Moreover, FISH with H1A resulted in interpretable signals on interphase nuclei in 88% of the cases, while the other probes yielded only dispersed overlapping signals

High-resolution comparative mapping among man, cattle and mouse suggests a role for repeat sequences in mammalian genome evolution

<p>Abstract</p> <p>Background</p> <p>Comparative mapping provides new insights into the evolutionary history of genomes. In particular, recent studies in mammals have suggested a role for segmental duplication in genome evolution. In some species such as Drosophila or maize, transposable elements (TEs) have been shown to be involved in chromosomal rearrangements. In this work, we have explored the presence of interspersed repeats in regions of chromosomal rearrangements, using an updated high-resolution integrated comparative map among cattle, man and mouse.</p> <p>Results</p> <p>The bovine, human and mouse comparative autosomal map has been constructed using data from bovine genetic and physical maps and from FISH-mapping studies. We confirm most previous results but also reveal some discrepancies. A total of 211 conserved segments have been identified between cattle and man, of which 33 are new segments and 72 correspond to extended, previously known segments. The resulting map covers 91% and 90% of the human and bovine genomes, respectively. Analysis of breakpoint regions revealed a high density of species-specific interspersed repeats in the human and mouse genomes.</p> <p>Conclusion</p> <p>Analysis of the breakpoint regions has revealed specific repeat density patterns, suggesting that TEs may have played a significant role in chromosome evolution and genome plasticity. However, we cannot rule out that repeats and breakpoints accumulate independently in the few same regions where modifications are better tolerated. Likewise, we cannot ascertain whether increased TE density is the cause or the consequence of chromosome rearrangements. Nevertheless, the identification of high density repeat clusters combined with a well-documented repeat phylogeny should highlight probable breakpoints, and permit their precise dating. Combining new statistical models taking the present information into account should help reconstruct ancestral karyotypes.</p

Specific cytogenetic labeling of bovine spermatozoa bearing X or Y chromosomes using fluorescent in situ hybridization (FISH)

X and Y specific probes were identified in order to apply the fluorescent in situ hybridization (FISH) technique to bovine spermatozoa. For Y chromosome detection, the BRY4a repetitive probe, covering three quarters of the chromosome, was used. For X chromosome detection, a goat Bacterial Artificial Chromosome (BAC) specific to the X chromosome of bovine and goats and giving a strong FISH signal was used. Each probe labeled roughly 45% of sperm cells. The hybridization method will be useful for evaluating the ratio of X- and Y- bearing spermatozoa in a sperm sample and consequently can be used to evaluate the efficiency of sperm sorting by different techniques such as flow cytometry

Cytogenetic mapping of 25 goat mammary gland Expressed Sequence Tags (ESTs)

Today, there is a shift towards a positional candidate approach in the molecular identification of genes. This study reports on an Expressed Sequence Tags (ESTs) mapping initiative in goats, based on sequence information gathered from a previous mammary gland cDNA systematic sequencing project. A total of 25 novel genes was localised cytogenetically on 16 goat chromosomes. Six of these ESTs were found to map to cattle milk QTL regions. These results made it possible to assess the use of ESTs as a shortcut to the molecular identification of some QTLs and as a valuable tool for comparative mapping

The prion or the related Shadoo protein is required for early mouse embryogenesis

AbstractThe prion protein PrP has a key role in transmissible spongiform encephalopathies but its biological function remains largely unknown. Recently, a related protein, Shadoo, was discovered. Its biological properties and brain distribution partially overlap that of PrP. We report that the Shadoo-encoding gene knockdown in PrP-knockout mouse embryos results in a lethal phenotype, occurring between E8 and E11, not observed on the wild-type genetic background. It reveals that these two proteins play a shared, crucial role in mammalian embryogenesis, explaining the lack of severe phenotype in PrP-knockout mammals, an appreciable step towards deciphering the biological role of this protein family

Cytogenetical anchoring of sheep linkage map and syntenic groups using a sheep BAC library

In order to simultaneously integrate linkage and syntenic groups to the ovine chromosomal map, a sheep bacterial artificial chromosome (BAC) library was screened with previously assigned microsatellites using a sheep-hamster hybrid panel and genetic linkage. Thirty-three BACs were obtained, fluorescently labelled and hybridised on sheep-goat hybrid metaphases (2n = 57). This study allowed us, (i), to anchor all linkage groups on sheep chromosomes, (ii), to give information on the probable position of the centromere on the linkage map for the centromeric chromosomes, (iii), to contradict the previous orientation of the ovine × linkage group by the mapping of BMS1008 on OARXq38. Concerning our somatic cell hybrid panel, this study resulted in the assignment of all the previously unassigned groups to ovine chromosomes and a complete characterisation of the hybrid panel. In addition, since hybridisations were performed on a sheep-goat hybrid, new marker/anchoring points were added to the caprine cytogenetic map

Impact of strong selection for the PrP major gene on genetic variability of four French sheep breeds (Open Access publication)

Effective selection on the PrP gene has been implemented since October 2001 in all French sheep breeds. After four years, the ARR "resistant" allele frequency increased by about 35% in young males. The aim of this study was to evaluate the impact of this strong selection on genetic variability. It is focussed on four French sheep breeds and based on the comparison of two groups of 94 animals within each breed: the first group of animals was born before the selection began, and the second, 3–4 years later. Genetic variability was assessed using genealogical and molecular data (29 microsatellite markers). The expected loss of genetic variability on the PrP gene was confirmed. Moreover, among the five markers located in the PrP region, only the three closest ones were affected. The evolution of the number of alleles, heterozygote deficiency within population, expected heterozygosity and the Reynolds distances agreed with the criteria from pedigree and pointed out that neutral genetic variability was not much affected. This trend depended on breed, i.e. on their initial states (population size, PrP frequencies) and on the selection strategies for improving scrapie resistance while carrying out selection for production traits