DNA Methylation in Drosophila

基因组印迹是一组染色体上的可逆和可区分的标记，由 传播者父母的性别。这种印记可能会极大地影响染色体行为或基因表达， 而适当印记的破坏可能会导致染色体丢失、癌症、出生缺陷或遗传病。一个 个体既有母系的印记，也有父系的印记，反映出其基因组的一半是从 每一位家长。这两套印记在生物体的整个生命中都稳定地保持着。在一些单元中(例如， 人类精子干细胞)，这种维持可能持续数千次的细胞分裂过程 世纪。当每条染色体传给下一代时，所有父母的印记都会被抹去，从而有利于 一组新的印记，适合传播者的性别。然而，由于印记是 通过未知的机制维护、建立和解释，尚不清楚印记是如何丢失的 会导致疾病。 我们的长期目标是了解男性和女性如何建立特定性别的印记， 并由后代维持，导致特定于父母的遗传行为。我们的具体假设 DNA甲基化是基因组印迹的一个重要但短暂的特征。我们把这一假设建立在 唯一已知dna甲基转移酶mt2突变果蝇的基因组印迹分析。我们的 初步数据表明，DNA甲基化是建立父系印记的母体所必需的， 这表明父亲的印记是由母亲的基因控制的。基于这些观察，我们 建议通过追求三个具体目标，将我们的研究重点放在印记建立上： 1.确定MT2的甲基化靶标DNA序列。我们将确定哪些序列 通过引入可打印的转基因而变得甲基化，在整个发育和有丝分裂后都是活跃的 成年，并监测DNA甲基化水平和染色质结构，因为它们与基因活性相关。 2.确定父系来源的染色体mt2活性的特异性模式。这把钥匙 基因组印迹的特征是区分父系和母系染色体，而不考虑 染色体序列。我们将重点测试可能的染色体歧视模型，包括 母本和父本基因组的基因活性定位和染色质结构的差异。 3.确定建立基因组印迹的遗传因素。我们发现了一种基因 包含建立母体印记所需的基因的间隔。我们将确定哪种基因是 参与母体印记的建立，并开始调查其行动模式。

Genomic imprinting is a reversible and differential mark on a set of chromosomes that is determined by the sex of the transmitting parent. This imprint may dramatically affect chromosome behavior or gene expression, and disruption of a proper imprint may result in chromosome loss, cancer, birth defects, or genetic disease. An individual has both maternal and paternal imprints, reflecting that half of its genome has been inherited from each parent. Both sets of imprints are stably maintained throughout the life of an organism. In some cells (e.g., human sperm stem cells), this maintenance may last through thousands of cell divisions over the course of a century. As each chromosome is transmitted to the next generation, all parental imprints are erased in favor of a new set of imprints appropriate to the sex of the transmitting individual. However, since the imprints are maintained, established, and interpreted through unknown mechanisms, it is not known how loss of imprinting leads to disease. Our long-term goal is to understand how sex-specific imprints are established by both males and females, and maintained by the offspring, resulting in parent-of-origin-specific genetic behaviors. Our specific hypothesis is that DNA methylation is an important but transient feature of genomic imprinting. We base this hypothesis on analysis of genomic imprints in fruit flies mutant for the sole known DNA methyltransferase, Mt2. Our preliminary data suggest that DNA methylation is required maternally for establishment of paternal imprints, indicating that the paternal imprint is controlled by the maternal genotype. Based on these observations, we propose to focus our research on imprint establishment by pursuing three specific aims: 1. Identify the DNA sequence that is targeted for methylation by Mt2. We will identify which sequences become methylated by introducing an imprintable transgene, active throughout development and post-mitotic adulthood, and monitoring DNA methylation levels and chromatin structure as they correlate with gene activity. 2. Determine the mode of specificity of Mt2activity for paternally-derived chromosomes. Thekey feature of genomic imprinting is the discrimination of paternal from maternal chromosomes, without regard to chromosome sequence. We will focus on testing possible models of chromosome discrimination, including localized gene activity and differences in chromatin structure of maternal and paternal genomes. 3. Identify genetic factors responsible for establishing genomic imprints. We have identified a genetic interval containing a gene required for the establishment of a maternal imprint. We will identify which gene is involved in maternal imprint establishment, and begin to investigate its mode of action.