Functional Analysis of the Drosophila melanogaster condensin subunit Cap-G

细胞周期中染色体的准确复制和分离是确保个体生物和整个种群遗传稳定性的先决条件。在参与调节这些过程的许多成分中，一种称为凝聚素的蛋白质复合物在塑造有丝分裂染色体中起着至关重要的作用，因此它们可以忠实地分布。许多生物体含有两种这样的凝聚素复合物（凝聚素I和II），这两种复合物都被证明是精确的染色体分布所必需的。在果蝇中，冷凝蛋白II似乎缺乏一种称为Cap-G2的成分。我们已经表明，冷凝蛋白I（Cap-G）的相应组件似乎并没有接管Cap-G2的作用，也不参与冷凝蛋白II的组装。由于我们的研究结果进一步质疑苍蝇中可溶性凝聚素II复合物的存在，因此果蝇中的凝聚素I是否接管了其他生物中描述的凝聚素II的所有功能是一个悬而未决的问题。在脊椎动物中，凝聚素II已被证明主要存在于细胞周期间期的细胞核中。它的功能之一是在DNA合成阶段启动复制的姐妹染色单体的分解。由于在果蝇Cap-G是唯一明确的核富集的凝聚素I-specific亚基在间期，我们的目标是分析Cap-G，单独或与其他凝聚素亚基组合，有助于脱离交织的姐妹染色单体后，他们的复制已经在S期。 此外，我们最近的Cap-G与其他蛋白质的关联研究表明，蛋白质Brahma（Brm）和Moira（Moi）与Cap-G一起特异性富集。 Brm和Moi是SWI/SNF染色质重塑复合物的组分，SWI/SNF染色质重塑复合物是一种分子机器，其有助于重组染色质以使其更易于转录。我们建议阐明是否有一个功能依赖的SWI/SNF行动上凝聚素，反之亦然，在果蝇。令人惊讶的是，一个基本上C-末端截短的变体的基本Cap-G仍然支持发展的生活苍蝇，即使374个氨基酸的缺乏，即使这种变体不再定位于细胞核。然而，由仅表达这种截短的Cap-G变体的母体产生的胚胎表现出严重降低的生存力。我们的目标是进一步解剖这种表型，以具体回答这个问题，是否是一个忠实的过渡，通过早期胚胎周期所需的Cap-G的核定位。

The accurate duplication and segregation of chromosomes during cell cycles is a prerequisite for ensuring genetic stability within an individual organism and entire populations. Among the many components involved in regulating these processes, a protein complex called condensin plays a crucial role in shaping mitotic chromosomes, so that they can be faithfully distributed. Many organisms contain two of these condensin complexes (condensin I and II), which both have been shown to be required for accurate chromosome distribution. In the fly Drosophila melanogaster, condensin II appears to lack one of its components, called Cap-G2. We have shown that the corresponding component of condensin I (Cap-G) does not seem to take over the role of Cap-G2 and does not participate in the assembly of condensin II. As our results furthermore questioned the very existence of a soluble condensin II complex in flies, it is an open question whether condensin I in Drosophila takes over all the functions of condensin II described in other organisms. In vertebrates, condensin II has been shown to reside primarily in the nucleus during interphase of the cell cycle. One of its functions is to initiate resolution of replicated sister chromatids already during the phase of DNA synthesis. As in Drosophila Cap-G is the only clearly nuclearly enriched condensin I-specifc subunit during interphase, we aim to analyze whether Cap-G, alone or in combination with other condensin subunits, helps to disengage the intertwined sister chromatids after their duplication already in S-phase. Furthermore, our recent association studies of Cap-G with other proteins have revealed that the proteins Brahma (Brm) and Moira (Moi) are specifically enriched together with Cap-G. Brm and Moi are components of the SWI/SNF chromatin remodelling complex, a molecular machine, which helps to restructure chromatin in order to make it more accessible for transcription. We propose to elucidate whether there is a functional dependence of SWI/SNF action on condensin, or vice versa, in Drosophila. Surprisingly, a substantially C-terminally truncated variant of the essential Cap-G still supports development of living flies, even though 374 amino acids are lacking and even though this variant no longer localizes to the nucleus. However, embryos produced by mothers expressing solely this truncated Cap-G variant exhibit a severely reduced viability. We aim at dissecting this phenotype further to specifically answer the question whether it is the nuclear localization of Cap-G which is required for a faithful transition through the early embryonic cycles.