RESUMO
Duplication and deletion of the 1.4-Mb region in 17p12 that is delimited by two 24-kb low copy number repeats (CMT1A-REPs) represent frequent genomic rearrangements resulting in two common inherited peripheral neuropathies, Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsy (HNPP). CMT1A and HNPP exemplify a paradigm for genomic disorders wherein unique genome architectural features result in susceptibility to DNA rearrangements that cause disease. A gene within the 1.4-Mb region, PMP22, is responsible for these disorders through a gene-dosage effect in the heterozygous duplication or deletion. However, the genomic structure of the 1.4-Mb region, including other genes contained within the rearranged genomic segment, remains essentially uncharacterized. To delineate genomic structural features, investigate higher-order genomic architecture, and identify genes in this region, we constructed PAC and BAC contigs and determined the complete nucleotide sequence. This CMT1A/HNPP genomic segment contains 1,421,129 bp of DNA. A low copy number repeat (LCR) was identified, with one copy inside and two copies outside of the 1.4-Mb region. Comparison between physical and genetic maps revealed a striking difference in recombination rates between the sexes with a lower recombination frequency in males (0.67 cM/Mb) versus females (5.5 cM/Mb). Hypothetically, this low recombination frequency in males may enable a chromosomal misalignment at proximal and distal CMT1A-REPs and promote unequal crossing over, which occurs 10 times more frequently in male meiosis. In addition to three previously described genes, five new genes (TEKT3, HS3ST3B1, NPD008/CGI-148, CDRT1, and CDRT15) and 13 predicted genes were identified. Most of these predicted genes are expressed only in embryonic stages. Analyses of the genomic region adjacent to proximal CMT1A-REP indicated an evolutionary mechanism for the formation of proximal CMT1A-REP and the creation of novel genes by DNA rearrangement during primate speciation.
Assuntos
Doença de Charcot-Marie-Tooth/genética , Deleção Cromossômica , Evolução Molecular , Duplicação Gênica , Genoma , Neuropatia Hereditária Motora e Sensorial/genética , Animais , Cromossomos Humanos Par 17/genética , Feminino , Dosagem de Genes , Humanos , Sequências Repetitivas Dispersas/genética , Masculino , Camundongos , Proteínas da Mielina/genética , Mapeamento Físico do Cromossomo , Pseudogenes , Recombinação Genética , Análise de Sequência de DNA/métodos , Sulfotransferases/genéticaRESUMO
The ord gene is required for proper segregation of all chromosomes in both male and female Drosophila meiosis. Here we describe the isolation of a null ord allele and examine the consequences of ablating ord function. Cytologically, meiotic sister-chromatid cohesion is severely disrupted in flies lacking ORD protein. Moreover, the frequency of missegregation in genetic tests is consistent with random segregation of chromosomes through both meiotic divisions, suggesting that sister cohesion may be completely abolished. However, only a slight decrease in viability is observed for ord null flies, indicating that ORD function is not essential for cohesion during somatic mitosis. In addition, we do not observe perturbation of germ-line mitotic divisions in flies lacking ORD activity. Our analysis of weaker ord alleles suggests that ORD is required for proper centromeric cohesion after arm cohesion is released at the metaphase I/anaphase I transition. Finally, although meiotic cohesion is abolished in the ord null fly, chromosome loss is not appreciable. Therefore, ORD activity appears to promote centromeric cohesion during meiosis II but is not essential for kinetochore function during anaphase.
Assuntos
Proteínas de Transporte/genética , Proteínas de Ciclo Celular , Centrômero/genética , Proteínas de Drosophila , Drosophila/genética , Mutação , Alelos , Animais , Proteínas de Transporte/fisiologia , Centrômero/fisiologia , Centrômero/ultraestrutura , Drosophila/fisiologia , Drosophila/ultraestrutura , Feminino , Deleção de Genes , Teste de Complementação Genética , Masculino , Meiose/genética , Troca de Cromátide Irmã/genética , Troca de Cromátide Irmã/fisiologia , Espermatócitos/ultraestruturaRESUMO
Attachment between the sister chromatids is required for proper chromosome segregation in meiosis and mitosis, but its molecular basis is not understood. Mutations in the Drosophila ord gene result in premature sister chromatid separation in meiosis, indicating that the product of this gene is necessary for sister chromatid cohesion. We isolated the ord gene and found that it encodes a novel 55 kDa protein. Some of the ord mutations exhibit unusual complementation properties, termed negative complementation, in which particular alleles poison the activity of another allele. Negative complementation predicts that protein-protein interactions are critical for ORD function. The position and nature of these unusual ord mutations demonstrate that the C-terminal half of ORD is essential for sister chromatid cohesion and suggest that it mediates protein binding.
