Trans-activation of the Drosophila Y Chromosome in Spermatogenesis

大量重复序列的存在是真核生物基因组最显著的特征之一。由于大多数重复元素没有明显的遗传功能，它们通常被认为是“自私的”或“垃圾”DNA。然而，越来越明显的是，这些序列可能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被证明可以调节基因表达。有人提出，酵母基因沉默是由端粒异染色质介导的，异染色质作为亚核细胞器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丰富的重复序列在果蝇中的功能。大约30%的果蝇基因组是由组成异染色质组成的，它包含高度重复的序列。果蝇的Y染色体是完全异色的，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6个易致雄性不育的基因。最近的分析表明，Y染色体携带一个反式激活子，调节雄性生殖系的转录。Y反式激活子分布在Y长臂上的一个独特区域，并且在功能上是冗余的，表明参与了异染色质重复序列。此外，反式激活子与分散在同一Y长区域内的遗传因素相关，这些遗传因素对精子发育至关重要。这些结果表明，Y反式激活子在精子发生中起着重要作用。进一步的遗传和分子研究表明，Y反式激活子与控制初级精母细胞转录的遗传途径相互作用。此外，该分析还确定了Y反式激活子的两个潜在靶基因，hsp26和hsp60ms基因，这两个基因都是精子发生所必需的。本项目有三个总体目标：(1)研究Y反式激活子在hsp26和hsp60ms基因上的转录调控。对hsp功能的研究将扩展到揭示Y转录激活子在精子发生中的作用。(2) Y反式激活子与精子发生过程中调节转录的途径分支相互作用的假设将得到验证，并将确定Y反式激活子是否通过调节精细胞个体化所需的一组特定基因来控制精子发生。(3)生成鉴定受Y反式激活子控制的hsp26调控序列的报告基因。位点定向诱变将用于精确定义这种顺式元件。本研究结果将为了解异色果蝇Y染色体的功能提供重要信息。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.