Identification and characterization of the meteor protein, a novel heterochromatin-related protein in Drosophila.

从大规模筛选的果蝇有丝分裂突变体中分离出一种新的有丝分裂突变体mtr^2，它显示有丝分裂细胞中含有高浓缩染色单体的比例很高，这些染色单体经历了后期分离，但分离被阻止了。用mtr^2对幼体中枢神经系统细胞进行细胞学检查，发现突变细胞的着丝粒处经常发生染色体断裂。mtr^2细胞含有异常纺锤体，纺锤体微管数量较少。在mtr^2细胞中，即使存在纺锤体缺陷，染色单体也可以在中期之前分离。mtr^2中异常的晚期样细胞含有与中期细胞正常水平相当的细胞周期蛋白B。在这些细胞学观察的基础上，我们提出了一个模型，即mtr^2的主要缺陷是着丝粒结构的扰动，它可能导致着丝粒上姐妹染色单体连接的丢失，并进一步导致有丝分裂纺锤体形成完成后有丝分裂检查点的活性状态释放失败。对mtr^2的遗传分析表明，该染色体包含两个独立的有丝分裂突变，一个新的致死突变l(3)acc6487和一个雌雄不育突变mtr^2。与着丝粒构建有关的有丝分裂表型与1 (3)acc6487突变相一致。另一方面，mtr基因对雄性果蝇减数分裂进入的负调控是必需的。mtr基因定位于多烯染色体的98C区，并通过质粒修复克隆了包含该基因的基因组区域。mtr基因与已知的编码红斑狼疮抗原相关蛋白a的dllap基因相对应。l(3)acc6487基因克隆的精细染色体定位正在进行中。

A novel mitotic mutant, mtr^2, which had been isolated from our large-scale screens of Drosophila mitotic mutants, showed a high proportion of mitotic cells containing hyper-condensed chromatids that have undergone anaphase separation but that the segregation was prevented. Cytological examination of cells in the larval central nervous system from mtr^2 revealed that chromosome fragmentation occurred frequently at centromeres in the mutant cells. The mtr^2 cells contained abnormal mitotic spindles consisted of a less number of spindle microtubules. In the mtr^2 cells, chromatid separation can occur before metaphase even though they have the spindle defects. The abnormal anaphase-like cells in mtr^2 contained a comparable level of cyclin B to the normal level in metaphase cells. On the base or these cytological observations, we proposed a model that the primary defect or the mtr^2 is a perturbation of centromer structure and that it possibly leads to a loss of sister chromatid connection at centromere and further results in a failure of release from an active state of mitotic checkpoint after a completion of mitotic spindle formation. Genetic analyses of the mtr^2 revealed that the chromosome contains two separate mitotic mutations, a novel lethal mutation l(3)acc6487 and a female and male sterile mutation mtr^2. The mitotic phenotypes concerned with construction of centromeres corresponded with the l(3)acc6487 mutation. On the other hand, the mtr gene is required for a negative regulation of meiotic entry in Drosophila males. The mtr gene was localized to 98C region on the polytene chromosome and cloned the genomic region including this gene by a plasmid rescue. The mtr gene corresponds to the known gene, dlarp encoding a of the Lupas Antigen-related protein. A fine chromosome mapping for gene cloning of the l(3)acc6487 is now underway.