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

一个新的有丝分裂突变体MTR^2是从我们大规模筛选的果蝇有丝分裂突变体中分离出来的，它显示出高比例的含有超浓缩染色单体的有丝分裂细胞已经进行了后期分离，但分离被阻止了。对MTR^2的幼虫中枢神经系统细胞的细胞学检查表明，突变细胞的着丝粒处经常出现染色体断裂。MTR^2细胞含有异常的纺锤体，由数量较少的纺锤体微管组成。在MTR^2细胞中，即使有纺锤体缺陷，染色单体也可以在中期之前分离。MTR^2中异常的后期样细胞中的细胞周期蛋白B含量与中期细胞中的正常水平相当。在这些细胞学观察的基础上，我们提出了一个模型，即初级缺陷或MTR^2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，进而导致在有丝分裂纺锤体形成完成后无法从有丝分裂检查点的活跃状态释放。对mtr^2的遗传分析表明，该染色体含有两个独立的有丝分裂突变，一个是新的致死突变L(3)acc6487，另一个是雌雄不育突变mtr^2。与着丝粒构建有关的有丝分裂表型与L(3)acc6487突变相对应。另一方面，MTR基因是雄性果蝇减数分裂进入负调控所必需的。将mtr基因定位于多线染色体上的98C区，并通过质粒拯救的方法克隆了含有该基因的基因组区域。MTR基因对应于已知的编码Lupas抗原相关蛋白a的基因dlarp。目前正在进行L(3)ACC6487基因克隆的精细染色体定位。

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.