Trans-activation of the Drosophila Y Chromosome in Spermatogenesis

真核生物基因组最显著的特征之一是存在大量的重复序列。 由于大多数重复元件没有明显的遗传功能，它们通常被视为“自私”或“垃圾”DNA。 然而，越来越明显的是，这些序列可以在调节基因表达中发挥重要作用。 例如，酵母端粒重复序列已显示出调节基因表达。 已经提出酵母中的基因沉默是由端粒异染色质介导的，端粒异染色质作为亚核细胞器来储存转录因子并调节其核浓度。 本研究计划的总体目标是阐明果蝇中丰富的重复序列的功能。 这种果蝇的基因组中大约30%是由组成型异染色质组成的，其中含有高度重复的序列。 果蝇的Y染色体完全是异染色质的，约占雄性基因组的13%。 尽管它的物理尺寸很大，但这条染色体只携带六个可突变为雄性不育的基因。 最近的分析表明，Y染色体携带一个反式激活因子，调节男性生殖细胞系的转录。 Y反式激活因子分布在Y长臂上的一个不同区域内，并且在功能上是冗余的，这表明涉及异染色质重复序列。 此外，反式激活因子与分散在相同Y长区域内的遗传因子相关，并且对精子发育至关重要。 这些结果表明Y反式激活因子在精子发生中起重要作用。 进一步的遗传和分子研究表明，Y反式激活因子与控制初级精母细胞转录的遗传途径相互作用。 此外，分析已经确定了Y反式激活因子的两个潜在的靶基因，hsp26和hsp60ms基因，这两个基因都是精子发生所需的。 本课题的主要目的是：（1）研究Y反式激活因子对hsp26和hsp60ms基因的转录调控。 热休克蛋白功能的研究将扩展到揭示Y反式激活因子在精子发生中的作用。 (2)将检验Y反式激活因子与调节精子发生中转录的途径的分支相互作用的假设，并确定Y反式激活因子是否通过调节精子细胞个体化所需的一组特定基因来控制精子发生。 (3)将产生报告基因以鉴定由Y反式激活因子控制的hsp26调节序列。 本研究将利用定点突变的方法对该顺式元件进行精确的定位，其结果将为异色果蝇Y染色体的功能研究提供重要的信息。 此外，了解果蝇异染色质如何发挥重要作用将有助于更好地理解所有异染色质的生物学意义，异染色质是几乎所有真核生物中的一个大的，但知之甚少的基因组成分。

The presence of abundant repetitive sequences is among the most conspicuouscharacteristics of eukaryotic genomes. Since most repetitive elements have no obvious genetic functions, they are often regarded as 'selfish' or 'junk' DNA. However, it has become increasingly evident that these sequences could play important roles in regulating gene expression. For example, the yeast telomeric repeats have been shown to regulate gene expression. It has been proposed that gene silencing in yeast is mediated by the telomeric heterochromatin that behaves as subnuclear organelles to store transcription factors and modulate their nuclear concentration. The overall objective of this research program is to elucidate the function of abundant repetitive sequences in the fruitfly Drosophila melanogaster. Approximately 30% of this fruitfly's genome is composed of constitutive heterochromatin, which contains highly repetitive sequences. The Drosophila Y chromosome is entirely heterochromatic and accounts for approximately 13% of a male genome. Despite its large physical size, this chromosome carries only six genes that are mutable to male sterility. Recent analysis has revealed that the Y chromosome carries a trans-activator that regulates transcription the male germ line. The Y trans-activator is distributed within a distinct region on the Y long arm and is functionally redundant, suggesting the involvement of heterochromatic repetitive sequences. In addition, the trans-activator is correlated with genetic factors that are dispersed within the same Y long region and are essential for sperm development. These results indicate that the Y trans-activator plays an important role in spermatogenesis. Further genetic and molecular studies have demonstrated that the Y trans-activator interacts with a genetic pathway that controls transcription in primary spermatocytes. In addition, the analysis has identified two potential target genes of the Y trans-activator, the hsp26 and hsp60ms genes, both of which are required for spermatogenesis. This project has three general goals: (1) The transcriptional regulation of the Y trans-activator on the hsp26 and hsp60ms genes will be investigated. Studies of the hsp function will be extended to reveal the effects of the Y transactivator in spermatogenesis. (2) The hypothesis that the Y trans-activator interacts with a branch of a pathway that regulates transcription in spermatogenesis will be tested and it will be determined whether the Y trans-activator controls spermatogenesis by regulating a specific set of genes required for spermatid individualization. (3) Reporter genes to identify the hsp26 regulatory sequence that is controlled by the Y trans-activator will be generated. Site-directed mutagenesis will be used to precisely define this cis-element.Results from thisresearch will provide important information about function of the heterocromatic Drosophila Y chromosome. Furthermore, knowing how Drosophila heterochromatin plays an essential role will help to better understand the biological significance of all heterochromatin, which is a large, yet poorly understood, genomic component in nearly all eukaryotic organisms.