Mutation of the MYH3 gene causes recessive cleft palate in Limousine cattle.

BACKGROUND: The palate is a structure separating the oral and nasal cavities and its integrity is essential for feeding and breathing. The total or partial opening of the palate is called a cleft palate and is a common malformation in mammals with environmental or hereditary aetiologies. Generally, it compromises life expectancy in the absence of surgical repair. A new form of non-syndromic cleft palate arose recently in Limousine cattle, with animals referred to the French National Observatory of Bovine Abnormalities since 2012. Since the number of affected animals has increased steadily, this study was undertaken to identify the cause of this disease. RESULTS: Based on pedigree analysis, occurrence of cleft palate in Limousine cattle was concordant with an autosomal recessive mode of inheritance. Genotyping of 16 affected animals and homozygosity mapping led to the identification of a single disease-associated haplotype on Bos taurus chromosome (BTA)19. The genome of two affected animals was sequenced, and their sequences were compared to the ARS-UCD1.2 reference genome to identify variants. The likely causal variants were compared to the variant database of the 1000 bull genome project and two fully linked mutations in exon 24 of the MYH3 (myosin heavy chain) gene were detected: a 1-bp non-synonymous substitution (BTA19:g.29609623A>G) and a 11-bp frameshift deletion (BTA19:g.29609605-29609615del). These two mutations were specific to the Limousine breed, with an estimated allele frequency of 2.4% and are predicted to be deleterious. The frameshift leads to a premature termination codon. Accordingly, mRNA and protein analyses in muscles from wild-type and affected animals revealed a decrease in MYH3 expression in affected animals, probably due to mRNA decay, as well as an absence of the MYH3 protein in these animals. MYH3 is mostly expressed in muscles, including craniofacial muscles, during embryogenesis, and its absence may impair palate formation. CONCLUSIONS: We describe a new form of hereditary cleft palate in Limousine cattle. We identified two fully linked and deleterious mutations, ultimately leading to the loss-of-function of the MYH3 protein. The mutations were included on the Illumina EuroG10k v8 and EuroGMD v1 SNP chips and are used to set up a reliable eradication strategy in the French Limousine breed.

Co-invalidation of Prnp and Sprn in FVB/N mice affects reproductive performances and highlight complex biological relationship between PrP and Shadoo.

Shadoo and PrP belongs to the same protein family, whose biological function remains poorly understood. Previous experiments reported potential functional redundancies or antagonisms between these two proteins, depending on the tissue analysed. While knockdown experiments suggested the requirement of Shadoo in the absence of PrP during early mouse embryogenesis, knockout ones, on the contrary, highlighted little impact, if any, of the double-knockout of these two loci. In the present study, we reinvestigated the phenotype associated with the concomitant knockout of these two genes using newly produced FVB/N Sprn knockout mice. In this genetic background, the combined two genes' knockout induces intra-uterine growth retardations, likely resulting from placental failures highlighted by transcriptomic analyses that revealed potential redundant or antagonist roles of these two proteins in different developmental-related pathways. It also induced an increased perinatal-lethality and ascertained the role of these two loci in the lactation process.

The Prion-like protein Shadoo is involved in mouse embryonic and mammary development and differentiation.

Shadoo belongs to the prion protein family, an evolutionary conserved and extensively studied family due to the implication of PrP in Transmissible Spongiform Encephalopathies. However, the biological function of these genes remains poorly understood. While Sprn-knockdown experiments suggested an involvement of Shadoo during mouse embryonic development, Sprn-knockout experiments in 129Pas/C57BL/6J or 129Pas/FVB/NCr mice did not confirm it. In the present study, we analyzed the impact of Sprn gene invalidation in a pure FVB/NJ genetic background, using a zinc finger nuclease approach. The in-depth analysis of the derived knockout transgenic mice revealed a significant increase in embryonic lethality at early post-implantation stages, a growth retardation of young Sprn-knockout pups fed by wild type mice and a lactation defect of Sprn-knockout females. Histological and transcriptional analyses of knockout E7.5 embryos, E14.5 placentas and G7.5 mammary glands revealed specific roles of the Shadoo protein in mouse early embryogenesis, tissue development and differentiation with a potential antagonist action between PrP and Shadoo. This study thus highlights the entanglement between the proteins of the prion family.

Survey of mitochondrial sequences integrated into the bovine nuclear genome.

Nuclear copies of the mitochondrial DNA (NUMTs) have already been described in several species. In this context, we identified and analysed 166 bovine NUMT regions with a total length of 430 kbp, representing about 0.02% of the cattle nuclear genome. Copies of all mitochondrial regions were detected in the nuclear genome, with distinct degrees of sequence similarity to the mitogenome. Some NUMT regions include large mitogenome segments and show high similarity to the organelle genome sequence. NUMT regions are frequently modified by insertion of repetitive sequences and by sequence rearrangements. We confirmed the existence of 29 NUMT regions by PCR amplification using DNA from the cow (Dominette) which was used to generate the bovine genome reference sequence, ruling out the possibility that these NUMTs could be artifacts of the genome assembly. As there are NUMT regions with high similarity to the mitogenome, special care is needed when designing primers for mitochondrial DNA amplification. Our results can therefore be used to avoid co-amplification of bovine nuclear sequences similar to mitochondrial DNA.

DNAJC2 is required for mouse early embryonic development.

DNAJC2 protein, also known as ZRF1 or MPP11, acts both as chaperone and as chromatin regulator. It is involved in stem cell differentiation and its expression is associated with various cancer malignancies. However, the role of Dnajc2 gene during mouse embryogenesis has not been assessed so far. To this aim, we invalidated Dnajc2 gene in FVB/Nj mice using the CrispR/Cas9 approach. We showed that this invalidation leads to the early post-implantation lethality of the nullizygous embryos. Furthermore, using siRNAs against Dnajc2 in mouse 1-cell embryos, we showed that maternal Dnajc2 mRNAs may allow for the early preimplantation development of these embryos. Altogether, these data demonstrate for the first time the requirement of DNAJC2 for early mouse embryogenesis.

Survey of allele specific expression in bovine muscle.

Allelic imbalance is a common phenomenon in mammals that plays an important role in gene regulation. An Allele Specific Expression (ASE) approach can be used to detect variants with a cis-regulatory effect on gene expression. In cattle, this type of study has only been done once in Holstein. In our study we performed a genome-wide analysis of ASE in 19 Limousine muscle samples. We identified 5,658 ASE SNPs (Single Nucleotide Polymorphisms showing allele specific expression) in 13% of genes with detectable expression in the Longissimus thoraci muscle. Interestingly we found allelic imbalance in AOX1, PALLD and CAST genes. We also found 2,107 ASE SNPs located within genomic regions associated with meat or carcass traits. In order to identify causative cis-regulatory variants explaining ASE we searched for SNPs altering binding sites of transcription factors or microRNAs. We identified one SNP in the 3'UTR region of PRNP that could be a causal regulatory variant modifying binding sites of several miRNAs. We showed that ASE is frequent within our muscle samples. Our data could be used to elucidate the molecular mechanisms underlying gene expression imbalance.

Progressive ataxia of Charolais cattle highlights a role of KIF1C in sustainable myelination.

Hereditary spastic paraplegias (HSPs) are clinically and genetically heterogeneous human neurodegenerative diseases. Amongst the identified genetic causes, mutations in genes encoding motor proteins such as kinesins have been involved in various HSP clinical isoforms. Mutations in KIF1C are responsible for autosomal recessive spastic paraplegia type 58 (SPG58) and spastic ataxia 2 (SPAX2). Bovines also develop neurodegenerative diseases, some of them having a genetic aetiology. Bovine progressive ataxia was first described in the Charolais breed in the early 1970s in England and further cases in this breed were subsequently reported worldwide. We can now report that progressive ataxia of Charolais cattle results from a homozygous single nucleotide polymorphism in the coding region of the KIF1C gene. In this study, we show that the mutation at the heterozygous state is associated with a better score for muscular development, explaining its balancing selection for several decades, and the resulting high frequency (13%) of the allele in the French Charolais breed. We demonstrate that the KIF1C bovine mutation leads to a functional knock-out, therefore mimicking mutations in humans affected by SPG58/SPAX2. The functional consequences of KIF1C loss of function in cattle were also histologically reevaluated. We showed by an immunochemistry approach that demyelinating plaques were due to altered oligodendrocyte membrane protrusion, and we highlight an abnormal accumulation of actin in the core of demyelinating plaques, which is normally concentrated at the leading edge of oligodendrocytes during axon wrapping. We also observed that the lesions were associated with abnormal extension of paranodal sections. Moreover, this model highlights the role of KIF1C protein in preserving the structural integrity and function of myelin, since the clinical signs and lesions arise in young-adult Charolais cattle. Finally, this model provides useful information for SPG58/SPAX2 disease and other demyelinating lesions.

Bovine and murine models highlight novel roles for SLC25A46 in mitochondrial dynamics and metabolism, with implications for human and animal health.

Neuropathies are neurodegenerative diseases affecting humans and other mammals. Many genetic causes have been identified so far, including mutations of genes encoding proteins involved in mitochondrial dynamics. Recently, the "Turning calves syndrome", a novel sensorimotor polyneuropathy was described in the French Rouge-des-Prés cattle breed. In the present study, we determined that this hereditary disease resulted from a single nucleotide substitution in SLC25A46, a gene encoding a protein of the mitochondrial carrier family. This mutation caused an apparent damaging amino-acid substitution. To better understand the function of this protein, we knocked out the Slc25a46 gene in a mouse model. This alteration affected not only the nervous system but also altered general metabolism, resulting in premature mortality. Based on optic microscopy examination, electron microscopy and on biochemical, metabolic and proteomic analyses, we showed that the Slc25a46 disruption caused a fusion/fission imbalance and an abnormal mitochondrial architecture that disturbed mitochondrial metabolism. These data extended the range of phenotypes associated with Slc25a46 dysfunction. Moreover, this Slc25a46 knock-out mouse model should be useful to further elucidate the role of SLC25A46 in mitochondrial dynamics.

Novel equine tissue miRNAs and breed-related miRNA expressed in serum.

BACKGROUND: MiRNAs regulate multiple genes at the post-transcriptional level and therefore play an important role in many biological processes. It has been suggested that miRNA exported outside the cells contribute to inter-cellular communication. Consequently, circulating miRNAs are of particular interest and are promising biomarkers for many diseases. The number of miRNAs annotated in the horse genome is much lower compared to model organisms like human and mouse. We therefore aimed to identify novel equine miRNAs for tissue types and breed in serum. RESULTS: We analysed 71 small RNA-seq libraries derived from nine tissues (gluteus medius, platysma, masseter muscle, heart, liver, cartilage, bone, total blood and serum) using miRDeep2 and miRdentify tools. Known miRNAs represented between 2.3 and 62.9 % of the reads in 71 libraries. A total of 683 novel miRNAs were identified. Breed and tissue type affected the number of miRNAs detected and interestingly, affected its average intensity. A total of 50 miRNAs in serum proved to be potential biomarkers to differentiate specific breed types, of which miR-122, miR-200, miR-483 were over-expressed and miR-328 was under-expressed in ponies compared to Warmbloods. The different miRNAs profiles, as well as the differences in their expression levels provide a foundation for more hypotheses based on the novel miRNAs discovered. CONCLUSIONS: We identified 683 novel equine miRNAs expressed in seven solid tissues, blood and serum. Additionally, our approach evidenced that such data supported identification of specific miRNAs as markers of functions related to breeds or disease tissues.

Integrated mRNA and miRNA expression profiling in blood reveals candidate biomarkers associated with endurance exercise in the horse.

The adaptive response to extreme endurance exercise might involve transcriptional and translational regulation by microRNAs (miRNAs). Therefore, the objective of the present study was to perform an integrated analysis of the blood transcriptome and miRNome (using microarrays) in the horse before and after a 160 km endurance competition. A total of 2,453 differentially expressed genes and 167 differentially expressed microRNAs were identified when comparing pre- and post-ride samples. We used a hypergeometric test and its generalization to gain a better understanding of the biological functions regulated by the differentially expressed microRNA. In particular, 44 differentially expressed microRNAs putatively regulated a total of 351 depleted differentially expressed genes involved variously in glucose metabolism, fatty acid oxidation, mitochondrion biogenesis, and immune response pathways. In an independent validation set of animals, graphical Gaussian models confirmed that miR-21-5p, miR-181b-5p and miR-505-5p are candidate regulatory molecules for the adaptation to endurance exercise in the horse. To the best of our knowledge, the present study is the first to provide a comprehensive, integrated overview of the microRNA-mRNA co-regulation networks that may have a key role in controlling post-transcriptomic regulation during endurance exercise.

Omics technologies provide new insights into the molecular physiopathology of equine osteochondrosis.

BACKGROUND: Osteochondrosis (OC(D)) is a juvenile osteo-articular disorder affecting several mammalian species. In horses, OC(D) is considered as a multifactorial disease and has been described as a focal disruption of endochondral ossification leading to the development of osteoarticular lesions. Nevertheless, OC(D) physiopathology is poorly understood. Affected horses may present joint swelling, stiffness and lameness. Thus, OC(D) is a major concern for the equine industry. Our study was designed as an integrative approach using omics technologies for the identification of constitutive defects in epiphyseal cartilage and/or subchondral bone associated with the development of primary lesions to further understand OC(D) pathology. This study compared samples from non-affected joints (hence lesion-free) from OC(D)-affected foals (n = 5, considered predisposed samples) with samples from OC-free foals (n = 5) considered as control samples. Consequently, results are not confounded by changes associated with the evolution of the lesion, but focus on altered constitutive molecular mechanisms. Comparative proteomics and micro computed tomography analyses were performed on predisposed and OC-free bone and cartilage samples. Metabolomics was also performed on synovial fluid from OC-free, OC(D)-affected and predisposed joints. RESULTS: Two lesion subtypes were identified: OCD (lesion with fragment) and OC (osteochondral defects). Modulated proteins were identified using omics technologies (2-DE proteomics) in cartilage and bone from affected foals compare to OC-free foals. These were associated with cellular processes including cell cycle, energy production, cell signaling and adhesion as well as tissue-specific processes such as chondrocyte maturation, extracellular matrix and mineral metabolism. Of these, five had already been identified in synovial fluid of OC-affected foals: ACTG1 (actin, gamma 1), albumin, haptoglobin, FBG (fibrinogen beta chain) and C4BPA (complement component 4 binding protein, alpha). CONCLUSION: This study suggests that OCD lesions may result from a cartilage defect whereas OC lesions may be triggered by both bone and cartilage defects, suggesting that different molecular mechanisms responsible for the equine osteochondrosis lesion subtypes and predisposition could be due to a defect in both bone and cartilage. This study will contribute to refining the definition of OC(D) lesions and may improve diagnosis and development of therapies for horses and other species, including humans.

Next-generation sequencing identifies equine cartilage and subchondral bone miRNAs and suggests their involvement in osteochondrosis physiopathology.

BACKGROUND: MicroRNAs (miRNAs) are an abundant class of small single-stranded non-coding RNA molecules ranging from 18 to 24 nucleotides. They negatively regulate gene expression at the post-transcriptional level and play key roles in many biological processes, including skeletal development and cartilage maturation. In addition, miRNAs involvement in osteoarticular diseases has been proved and some of them were identified as suitable biomarkers for pathological conditions. Equine osteochondrosis (OC) is one of the most prevalent juvenile osteoarticular disorders in horses and represents a major concern for animal welfare and economic reasons. Its etiology and pathology remain controversial and biological pathways as well as molecular mechanisms involved in the physiopathology are still unclear. This study aims to investigate the potential role of miRNAs in equine osteochondrosis (OC) physiopathology.Short-read NGS technology (SOLID™, Life Technologies) was used to establish a comprehensive repertoire of miRNA expressed in either equine cartilage or subchondral bone. Undamaged cartilage and subchondral bone samples from healthy (healthy samples) and OC-affected (predisposed samples) 10-month Anglo-Arabian foals were analysed. Samples were also subjected or not to an experimental mechanical loading to evaluate the role of miRNAs in the regulation of mechano-transduction pathways. Predicted targets of annotated miRNAs were identified using miRmap. RESULTS: Epiphyseal cartilage and subchondral bone miRNome were defined, including about 300 new miRNAs. Differentially expressed miRNAs were identified between bone and cartilage from healthy and OC foals, as well as after an experimental mechanical loading. In cartilage, functional annotation of their predicted targets suggests a role in the maintenance of cartilage integrity through the control of cell cycle and differentiation, energy production and metabolism as well as extracellular matrix structure and dynamics. In bone, miRNA predicited targets were associated with osteoblasts and osteoclasts differentiation, though the regulation of energy production, vesicle transport and some growth factor signaling pathways. CONCLUSION: Taken together, our results suggest a role of miRNAs in equine OC physiopathology and in the cellular response to biomechanical stress in cartilage and bone. In silico target prediction and functional enrichment analysis provides new insight into OC molecular physiopathology.

LIPH expression in skin and hair follicles of normal coat and Rex rabbits.

Natural mutations in the LIPH gene were shown to be responsible for hair growth defects in humans and for the rex short hair phenotype in rabbits. In this species, we identified a single nucleotide deletion in LIPH (1362delA) introducing a stop codon in the C-terminal region of the protein. We investigated the expression of LIPH between normal coat and rex rabbits during critical fetal stages of hair follicle genesis, in adults and during hair follicle cycles. Transcripts were three times less expressed in both fetal and adult stages of the rex rabbits than in normal rabbits. In addition, the hair growth cycle phases affected the regulation of the transcription level in the normal and mutant phenotypes differently. LIPH mRNA and protein levels were higher in the outer root sheath (ORS) than in the inner root sheath (IRS), with a very weak signal in the IRS of rex rabbits. In vitro transfection shows that the mutant protein has a reduced lipase activity compared to the wild type form. Our results contribute to the characterization of the LIPH mode of action and confirm the crucial role of LIPH in hair production.

A deletion in exon 9 of the LIPH gene is responsible for the rex hair coat phenotype in rabbits (Oryctolagus cuniculus).

The fur of common rabbits is constituted of 3 types of hair differing in length and diameter while that of rex animals is essentially made up of amazingly soft down-hair. Rex short hair coat phenotypes in rabbits were shown to be controlled by three distinct loci. We focused on the "r1" mutation which segregates at a simple autosomal-recessive locus in our rabbit strains. A positional candidate gene approach was used to identify the rex gene and the corresponding mutation. The gene was primo-localized within a 40 cM region on rabbit chromosome 14 by genome scanning families of 187 rabbits in an experimental mating scheme. Then, fine mapping refined the region to 0.5 cM (Z = 78) by genotyping an additional 359 offspring for 94 microsatellites present or newly generated within the first defined interval. Comparative mapping pointed out a candidate gene in this 700 kb region, namely LIPH (Lipase Member H). In humans, several mutations in this major gene cause alopecia, hair loss phenotypes. The rabbit gene structure was established and a deletion of a single nucleotide was found in LIPH exon 9 of rex rabbits (1362delA). This mutation results in a frameshift and introduces a premature stop codon potentially shortening the protein by 19 amino acids. The association between this deletion and the rex phenotype was complete, as determined by its presence in our rabbit families and among a panel of 60 rex and its absence in all 60 non-rex rabbits. This strongly suggests that this deletion, in a homozygous state, is responsible for the rex phenotype in rabbits.

Chromosomal distribution of endogenous Jaagsiekte sheep retrovirus proviral sequences in the sheep genome.

A family of endogenous retroviruses (enJSRV) closely related to Jaagsiekte sheep retrovirus (JSRV) is ubiquitous in domestic and wild sheep and goats. Southern blot hybridization studies indicate that there is little active replication or movement of the enJSRV proviruses in these species. Two approaches were used to investigate the distribution of proviral loci in the sheep genome. Fluorescence in situ hybridization (FISH) to metaphase chromosome spreads using viral DNA probes was used to detect loci on chromosomes. Hybridization signals were reproducibly detected on seven sheep chromosomes and eight goat chromosomes in seven cell lines. In addition, a panel of 30 sheep-hamster hybrid cell lines, each of which carries one or more sheep chromosomes and which collectively contain the whole sheep genome, was examined for enJSRV sequences. DNA from each of the lines was used as a template for PCR with JSRV gag-specific primers. A PCR product was amplified from 27 of the hybrid lines, indicating that JSRV gag sequences are found on at least 15 of the 28 sheep chromosomes, including those identified by FISH. Thus, enJSRV proviruses are essentially randomly distributed among the chromosomes of sheep and goats. FISH and/or Southern blot hybridization on DNA from several of the sheep-hamster hybrid cell lines suggests that loci containing multiple copies of enJSRV are present on chromosomes 6 and 9. The origin and functional significance of these arrays is not known.

Activin signaling pathways in ovine pituitary and LbetaT2 gonadotrope cells.

In the pituitary, activin stimulates the synthesis and release of FSH. However, the activin receptor signaling pathways that mediate these effects are poorly known. We investigated these mechanisms in primary ovine pituitary cells (POP) and in the murine LbetaT2 gonadotrope cell line. POP cells and LbetaT2 cells express the different activin receptors (types IA, IB, IIA, and IIB) and the Smad proteins (Smad-2, -3, -4, and -7). In both POP and LbetaT2 cells, activin activated several signaling pathways: Smad-2, extracellular regulated kinase-1/2 (ERK1/2), p38, and phosphatidylinositol 3'-kinase (PI3K)/Akt. Phosphorylation of ERK1/2 and p38 were stimulated (3- to 6-fold) rapidly in 5 min, whereas activation of both Smad-2 and Akt (3- to 5-fold) occurred later, in 60 min. Activin also increased the association of activin receptor IIB with PI3K. Using specific inhibitors, we demonstrated that the activation of Smad-2 was partially blocked by the inhibition of PI3K but not by the inhibition of ERK1/2 or p38, suggesting a cross-talk between the Smad and PI3K/Akt pathways. In both POP and LbetaT2 cells, FSH expression and secretion in response to activin were not altered by the inhibition of PI3K/Akt, ERK1/2, or p38 pathways, whereas they were reduced by about 2-fold by expression of a dominant negative of Smad-2 or the natural inhibitory Smad-7 in LbetaT2 cells. These results indicate that activin activates several signaling pathways with different time courses in both POP and LbetaT2 cells, but only the Smad-2 pathway appears to be directly implicated in FSH expression and release in LbetaT2 cells.

Expression profiles and chromosomal localization of genes controlling meiosis and follicular development in the sheep ovary.

In female sheep fetuses, two of the most crucial stages of ovarian development are prophase of meiosis I and follicle formation. In the present study, sheep ovaries collected on Days 25, 38, 49, 56, 67, 75, 94, and 120 of gestation, at birth, and in adulthood were tested by reverse transcription-polymerase chain reaction (RT-PCR) for the expression of 14 genes known to be involved in the ovarian differentiation in diverse organisms. The aim of this study was to determine 1) the expression pattern of six genes involved in germ cell development or meiosis (DMC1, SPO11, MSH4, MSH5, DAZL, and Boule) and five ovary-derived factors (OVOL1, SIAH2, DIAPH2, FOXL2, and FGF9), 2) the onset of gene expression for several members of the bone morphogenetic protein (BMP) pathway involved in follicular development (GDF9, BMP15, BMPR-IB), and 3) the chromosomal localization of seven of these genes in the sheep genome. The RT-PCR analysis revealed that the two germline-specific genes, DAZL and Boule, were expressed between 49 and 94 days postcoitum (dpc) with a similar pattern to typical meiosis genes (DMC1, MSH4, and MSH5), suggesting their possible participation in prophase of meiosis I. GDF9 and OVOL1 gene transcription started at 56 dpc and extended until birth, while BMP15 presented a more restricted window of expression between 94 dpc and birth, corresponding to the formation of first growing follicles. The homologous ovine genes for SPO11, DMC1, MSH5, DAZL, FGF9, DIAPH2, and SIAH2 were located on OAR 13q21-22, 3q35, 20q22, 19q13, 10q15, Xq44, and 1q41-42, respectively. In sheep, quantitative trait loci affecting female reproductive capacities are currently being detected. The ontology and precise mapping of ovarian genes will be useful to identify potential candidate genes that might underlie these effects.

Cytogenetic localization of 136 genes in the horse: comparative mapping with the human genome.

The aim of this study was to increase the number of type I markers on the horse cytogenetic map and to improve comparison with maps of other species, thus facilitating positional candidate cloning studies. BAC clones from two different sources were FISH mapped: homologous horse BAC clones selected from our newly extended BAC library using consensus primer sequences and heterologous goat BAC clones. We report the localization of 136 genes on the horse cytogenetic map, almost doubling the number of cytogenetically mapped genes with 48 localizations from horse BAC clones and 88 from goat BAC clones. For the first time, genes were mapped to ECA13p, ECA29, and probably ECA30. A total of 284 genes are now FISH mapped on the horse chromosomes. Comparison with the human map defines 113 conserved segments that include new homologous segments not identified by Zoo-FISH on ECA7 and ECA13p.

Sheep/human comparative map in a chromosome region involved in scrapie incubation time shows multiple breakpoints between human chromosomes 14 and 15 and sheep chromosomes 7 and 18.

A chromosome region involved in scrapie incubation time was identified on sheep chromosome 18 (OAR18). Since OAR18 (and OAR7) share conserved chromosome segments with human chromosomes HSA14 and HSA15, a dense map of type I markers was constructed by FISH mapping of bacterial artificial chromosomes containing genes located on these human chromosomes. In this study, we used the complete human sequence information (gene positions in megabases, Mb) to locate approximately one gene every 2 Mb on HSA15 (19 genes mapped between 19.51 and 66.02 Mb) and on HSA14 (11 genes between 73.24 and 102.62 Mb). Combined with previous work carried out in cattle and goats, our results made it possible to refine the comparative map between ruminants and humans for these two highly rearranged chromosomes (10 segments on HSA15 and 7 on HSA14). Furthermore, we identified relatively short intervals containing evolutionary breakpoints, which is a prerequisite to position them precisely. This work is also the first step in the cloning of the region involved in scrapie incubation period in sheep.