CEP250 is Required for Maintaining Centrosome Cohesion in the Germline and Fertility in Male Mice.

Male gametogenesis involves both mitotic divisions to amplify germ cell progenitors that gradually differentiate and meiotic divisions. Centrosomal regulation is essential for both types of divisions, with centrioles remaining tightly paired during the interphase. Here, we generated and characterized the phenotype of mutant mice devoid of Cep250/C-Nap1, a gene encoding for a docking protein for fibers linking centrioles, and characterized their phenotype. The Cep250 -/- mice presented with no major defects, apart from male infertility due to a reduction in the spermatogonial pool and the meiotic blockade. Spermatogonial stem cells expressing Zbtb16 were not affected, whereas the differentiating spermatogonia were vastly lost. These cells displayed abnormal γH2AX-staining, accompanied by an increase in the apoptotic rate. The few germ cells that survived at this stage, entered the meiotic prophase I and were arrested at a pachytene-like stage, likely due to synapsis defects and the unrepaired DNA double-strand breaks. In these cells, centrosomes split up precociously, with γ-tubulin foci being separated whereas these were closely associated in wild-type cells. Interestingly, this lack of cohesion was also observed in wild-type female meiocytes, likely explaining the normal fertility of Cep250 -/- female mice. Taken together, this study proposes a specific requirement of centrosome cohesion in the male germline, with a crucial role of CEP250 in both differentiating spermatogonia and meiotic spermatocytes.

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.

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.

C-Nap1 mutation affects centriole cohesion and is associated with a Seckel-like syndrome in cattle.

Caprine-like Generalized Hypoplasia Syndrome (SHGC) is an autosomal-recessive disorder in Montbéliarde cattle. Affected animals present a wide range of clinical features that include the following: delayed development with low birth weight, hind limb muscular hypoplasia, caprine-like thin head and partial coat depigmentation. Here we show that SHGC is caused by a truncating mutation in the CEP250 gene that encodes the centrosomal protein C-Nap1. This mutation results in centrosome splitting, which neither affects centriole ultrastructure and duplication in dividing cells nor centriole function in cilium assembly and mitotic spindle organization. Loss of C-Nap1-mediated centriole cohesion leads to an altered cell migration phenotype. This discovery extends the range of loci that constitute the spectrum of autosomal primary recessive microcephaly (MCPH) and Seckel-like syndromes.

Characterization of the ovine ribosomal protein SA gene and its pseudogenes.

BACKGROUND: The ribosomal protein SA (RPSA), previously named 37-kDa laminin receptor precursor/67-kDa laminin receptor (LRP/LR) is a multifunctional protein that plays a role in a number of pathological processes, such as cancer and prion diseases. In all investigated species, RPSA is a member of a multicopy gene family consisting of one full length functional gene and several pseudogenes. Therefore, for studies on RPSA related pathways/pathologies, it is important to characterize the whole family and to address the possible function of the other RPSA family members. The present work aims at deciphering the RPSA family in sheep. RESULTS: In addition to the full length functional ovine RPSA gene, 11 other members of this multicopy gene family, all processed pseudogenes, were identified. Comparison between the RPSA transcript and these pseudogenes shows a large variety in sequence identities ranging from 99% to 74%. Only one of the 11 pseudogenes, i.e. RPSAP7, shares the same open reading frame (ORF) of 295 amino acids with the RPSA gene, differing in only one amino acid. All members of the RPSA family were annotated by comparative mapping and fluorescence in situ hybridization (FISH) localization. Transcription was investigated in the cerebrum, cerebellum, spleen, muscle, lymph node, duodenum and blood, and transcripts were detected for 6 of the 11 pseudogenes in some of these tissues. CONCLUSIONS: In the present work we have characterized the ovine RPSA family. Our results have revealed the existence of 11 ovine RPSA pseudogenes and provide new data on their structure and sequence. Such information will facilitate molecular studies of the functional RPSA gene taking into account the existence of these pseudogenes in the design of experiments. It remains to be investigated if the transcribed members are functional as regulatory non-coding RNA or as functional proteins.

Characterization, chromosomal assignment, and role of LIFR in early embryogenesis and stem cell establishment of rabbits.

Leukemia inhibitory factor (LIF) is a multifunctional cytokine with an important role during early embryonic development, implantation, and as an inhibitor of murine embryonic stem cell differentiation. It exerts its effects by binding to the leukemia inhibitory factor receptor, a heterodimer of two transmembrane proteins, the specific leukemia inhibitory factor receptor subunit, and the common gp130. A partial cDNA clone coding for the membrane-bound form of the specific rabbit leukemia inhibitory factor receptor was isolated from the genital ridge of 13.5 days postcoitum fetus. Fluorescent in situ hybridization analysis revealed that the rabbit leukemia inhibitory factor receptor gene is located on chromosome OCU11p11.1. It has been shown that the membrane-bound rabbit leukemia inhibitory factor receptor mRNA is expressed during embryo implantation but not at earlier developmental stages. Rabbit embryonic stem cell-like line establishment is improved in the presence of LIF, and those cells express both leukemia inhibitory factor and its receptor. The withdrawal of leukemia inhibitory factor results the differentiation of embryonic stem cell-like cells to beating myocardial-like cells. Our findings suggest that the self-renewal mechanism is similar in mouse and rabbit embryonic stem cells, and expands our knowledge on the role of the LIF-LIFR signal pathway in early rabbit embryogenesis and rabbit embryonic stem cell establishment.

Structural and functional analysis of the HSP90AA1 gene: distribution of polymorphisms among sheep with different responses to scrapie.

Scrapie is a transmissible spongiform encephalopathy in sheep and goats. Susceptibility to this neurodegenerative disease is mainly controlled by point mutations at the PRNP locus. Other genes, apart from PRNP, have been reported to modulate resistance/susceptibility to scrapie. On the basis of several studies in Alzheimer and different transmissible spongiform encephalopathy models, HSP90AA1 was chosen as a putative positional and functional candidate gene that might be involved in the polygenic variance mentioned above. In the present work, the ovine HSP90AA1 gene including the promoter and other regulatory regions has been isolated and characterized. Several sequence polymorphisms have also been identified. FISH-mapping localized the HSP90AA1 gene on ovine chromosome OAR19q24dist, which was confirmed by linkage analysis. This chromosome region has been shown to include a quantitative trait loci (QTL) for scrapie incubation period in sheep. Expression analyses were carried out in spleen and cerebellum samples. No differences in the expression of the HSP90AA1 gene were found in any of these tissues (p > 0.05) between control and infected animal samples. Nevertheless, association analyses revealed that several polymorphisms in the 5' and 3' regions of the HSP90AA1 gene were differentially distributed among animals with different responses to scrapie infection. Thus, results presented here support the hypothesis that HSP90AA1 could be a positional and functional candidate gene modulating the response to scrapie in sheep.

Structural and functional analysis of the ovine laminin receptor gene (RPSA): Possible involvement of the LRP/LR protein in scrapie response.

Scrapie is a prion disease affecting sheep and goats. Susceptibility to this neurodegenerative disease shows polygenic variance. The involvement of the laminin receptor (LRP/LR) in the metabolism and propagation of prions has previously been demonstrated. In the present work, the ovine laminin receptor gene (RPSA) was isolated, characterized, and mapped to ovine chromosome OAR19q13. Real-time RT-PCR revealed a significant decrease in RPSA mRNA in cerebellum after scrapie infection. Conversely, no differences were detected in other brain regions such as diencephalon and medulla oblongata. Association analysis showed that a polymorphism reflecting the presence of a RPSA pseudogene was overrepresented in a group of sheep resistant to scrapie infection. No amino acid change in the LRP/LR protein was found in the 126 sheep analyzed. However, interesting amino acid positions (241, 272, and 290), which could participate in the species barrier to scrapie and maybe to other transmissible spongiform encephalopathies, were identified by comparing LRP/LR sequences from various mammals with variable levels of resistance to scrapie.

IL-1 family members as candidate genes modulating scrapie susceptibility in sheep: localization, partial characterization, and expression.

Scrapie (SC) is a transmissible spongiform encephalopathy (TSE) in sheep and goats. Susceptibility to this neurodegenerative disease is controlled mainly by point mutations at the PRNP locus. Other genes, apart from PRNP, have been reported to modulate resistance/susceptibility to SC. On the basis of several studies on Alzheimer's disease and different TSE models, and of requirement for correct homeostasis of cytokines in brain, IL1B and IL1RN were chosen as putative positional and functional candidate genes that might be involved in the polygenic variance mentioned above. In the present work, ovine IL1B and IL1RN genes were partially isolated and characterized, including promoter and other regulatory regions. In addition, several sequence polymorphisms were identified. Furthermore, their cytogenetic positions on sheep chromosomes were determined by FISH and confirmed by linkage analysis, localizing both genes in OAR3p22, a region previously described as carrying a QTL for SC incubation period in sheep. Finally, expression analyses were carried out in eight naturally SC-infected and five uninfected sheep with the same genotype for PRNP (ARQ/ARQ). This comparison was performed using real-time RT-PCR in samples of spleen and cerebellum. Results showed differences in the expression of both cytokines in cerebellum (p < 0.05) but not in spleen (p > 0.05).

Construction of a cytogenetically anchored microsatellite map in rabbit.

Rabbit (Oryctolagus cuniculus) represents a valuable source of biomedical models and corresponds to a small but active economic sector in Europe for meat and fur. The rabbit genome has not been thoroughly studied until recently, and high-resolution maps necessary for identification of genes and quantitative trait loci (QTL) are not yet available. Our aim was to isolate over 300 new and regularly distributed (TG)n or (TC)n rabbit microsatellites. To achieve this purpose, 164 microsatellite sequences were isolated from gene-containing bacterial artificial chromosome (BAC) clones previously localized by fluorescence in situ hybridization (FISH) on all the rabbit chromosomes. In addition, 141 microsatellite sequences were subcloned from a plasmid genomic library, and for 41 of these sequences, BAC clones were identified and FISH-mapped. TC repeats were present in 62% of the microsatellites derived from gene-containing BAC clones and in 22% of those from the plasmid genomic library, with an average of 42.9% irrespective of the microsatellite origin. These results suggest a higher proportion of (TC)n repeats and a nonhomogeneous distribution of (TG)n and (TC)n repeats in the rabbit genome compared to those in man. Among the 305 isolated microsatellites, 177 were assigned to 139 different cytogenetic positions on all the chromosomes except rabbit Chromosome 21. Sequence similarity searches provided hit locations on the Human Build 35a and hypothetical assignments on rabbit chromosomes for ten additional microsatellites. Taken together, these results report a reservoir of 305 new rabbit microsatellites of which 60% have a cytogenetic position. This is the first step toward the construction of an integrated cytogenetic and genetic map based on microsatellites homogeneously anchored to the rabbit genome.