Transferred genes and endosymbiosis

转移基因和内共生西德尼·K·皮尔斯南佛罗里达大学成功地在两个生物体之间转移功能基因是基因转移治疗的目标和基因改造技术的基础。基因转移也是线粒体和叶绿体内共生起源的理论基础，是原核生物进化的重要机制，甚至被认为是早期生化进化的主要力量。基因转移的研究包括尝试插入纠正的基因以抵消缺陷基因的存在，以改善或治愈各种人类疾病，或者通过将新的或改变的基因转移到宿主DNA中来改变作物、牲畜或细胞培养的特定特征。这项研究的很大一部分涉及到将感兴趣的基因机械转移到宿主细胞中，但最近利用病毒载体进行的转移已经开发出来。在真核系统中，大多数研究都集中在含有细胞器的DNA和核基因组之间的基因转移机制上，特别是从高等植物的线粒体转移。尽管已经取得了重大进展，但关于多细胞生物体之间基因转移的自然发生机制的信息仍然很少。到目前为止，几乎所有的信息都来自对转移的研究，其中至少有一种生物是原核生物。发现基因成功转移的机制，以及将外来基因整合和表达到宿主细胞中，对于理解这一过程以及一般的进化都是至关重要的。然而，研究基因转移机制的一个主要困难是找到一个自然发生的系统，在这个系统中发生了明显的、成功的基因转移事件。研究人员似乎发现了两个案例，功能基因在来自两个真核王国的两个生物之间转移。此外，可疑基因被传递给宿主细胞谱系中的后续世代。这一发现来自对叶绿体共生的长期研究，这是一种有趣的现象，通常来自特定藻类的叶绿体被动物(或原生动物)细胞吞噬，并在宿主细胞内继续进行一段时间的光合作用。我们一直在研究这种关联，使用了两种海鞘鼻涕虫，一种是氯化鬼针藻，另一种是皱叶鬼针藻。利用药理学和分子生物学技术，我们已经证明了至少有一种叶绿体蛋白--岩藻黄质-叶绿素结合蛋白(FCP)被合成，而该叶绿体存在于该虫细胞的细胞质中，并且我们通过Southern杂交分析在该虫基因组DNA中发现了FCP基因序列。我们也为其他几种叶绿体蛋白找到了类似的证据。这些发现使我们得出这样的假设，即编码叶绿体蛋白的基因已经从藻类转移到动物细胞基因组中。如果假设是正确的，基因在多细胞物种之间的传递可能是一种重要的进化机制，而海参将为确定功能基因在多细胞生物之间转移的机制以及解释细胞细胞器的内共生起源提供一个很好的模式系统。因此，这项提议的具体目的是确定这两个多细胞物种之间基因转移的性质，并开始确定可能的机制。我们的实验将依靠分子生物学和电子显微镜的分辨率来确定叶绿体-鼻涕虫结合的分子和细胞生物学的性质。两种鼻涕虫之间的比较应该会为结果增加重要的信息。

Transferred genes and endosymbiosisSidney K PierceUniversity of South FloridaThe successful transfer of functional genes between two organisms is the objective of gene transfer therapy and the basis of genetic modification technology. Gene transfer is also the theoretical foundation of the endosymbiotic origin of mitochondria and chloroplasts, is an important mechanism of evolution amongst prokaryotes and has even been proposed as a major force in early biochemical evolution. Research on gene transfer has included attempts to insert corrected genes to offset the presence of defective genes to improve or cure various human diseases or to change particular characteristics of crop plants, livestock or cell cultures by transferring a novel or altered gene into host DNA. Much of this research has involved the mechanical transfer of the gene of interest into the host cell, but lately transfers using viral vectors have been developed. In eukaryotic systems, most research has been focused on the mechanism of gene transfer between DNA containing organelles and the nuclear genome, particularly from mitochondria in higher plants. In spite of the significant progress that has been made, there is only a little information about naturally occurring mechanisms of transfer of genes between multicellular organisms. Virtually all information to date has come from studies of transfers where at least one of the organisms is prokaryotic. Discovering the mechanisms underlying the successful transfer of a gene, as well as incorporation and expression of a foreign gene into a host cell is essential to understanding both the process, as well as evolution, in general. However, a major difficulty to studying gene transfer mechanisms is finding a naturally occurring system where an obvious, successful, gene transfer event has occurred.The investigators appears to have found two cases where functional genes have been transferred between two organisms from two eukaryotic kingdoms. Furthermore, the suspect genes are transmitted to subsequent generations in the host cell lineage. This discovery came from a long term investigation of a chloroplast symbiosis, an intriguing phenomenon in which chloroplasts, usually from a specific species of alga, are engulfed by an animal (or protistan) cell and continue to photosynthesize inside the host cell for a period of time. We have been investigating such an association using two species of ascoglossan sea slugs Elysia chlorotica and Elysia crispata. Using both pharmacological and molecular techniques we have shown that at least one chloroplast protein, fucoxanthin-chlorophyll binding protein (FCP) is synthesized while the plastid resides in the cytoplasm of the slug cell and we have found the FCP gene sequence in slug genomic DNA using southern blot analysis. We have also developed similar evidence for several other plastid proteins. These discoveries have led us to the hypothesis that genes coding for chloroplast proteins have been transferred from the alga into the animal cell genome. If the hypothesis is correct, transmission of genes between multicellular species may be an important evolutionary mechanism and the sea slugs will provide an excellent model system for determining the mechanisms underlying the transfer of functional genes between multicellular organisms, as well as explaining the endosymbiotic origin of cellular organelles. So, the specific aims of this proposal are to determine the nature of the gene transfer between these two multicellular species and begin to determine the possible mechanism. Our experiments will rely on the resolving power of molecular biology and electron microscopy to determine the nature of the molecular and cell biology of the plastid-slug association. Comparisons between the two species of slugs should add important information to the results.