Transferred genes and endosymbiosis

移植基因和内共生西德尼·K·皮尔斯南佛罗里达大学功能基因在两种生物体之间的成功移植是基因移植治疗的目标，也是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。对基因转移的研究包括试图插入纠正的基因以抵消存在缺陷的基因，以改善或治愈各种人类疾病，或通过将一种新的或改变的基因转移到宿主DNA中来改变农作物、牲畜或细胞培养物的特定特征。这方面的许多研究都涉及到将感兴趣的基因机械转移到宿主细胞中，但最近使用病毒载体的转移已经发展起来。在真核生物系统中，大多数研究都集中在含有DNA的细胞器和核基因组之间的基因转移机制上，特别是在高等植物的线粒体中。尽管已经取得了重大进展，但关于多细胞生物之间自然发生的基因转移机制的信息却很少。迄今为止，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体是原核生物。发现基因成功转移的机制，以及外源基因在宿主细胞中的结合和表达，对于理解这一过程以及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，其中一个明显的、成功的基因转移事件已经发生。研究人员似乎发现了两个案例，其中功能基因在两个真核生物王国的两个生物体之间转移。此外，可疑基因在宿主细胞系中被传递给后代。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，叶绿体通常来自一种特定的藻类，被动物（或原生生物）细胞吞没，并在宿主细胞内继续进行一段时间的光合作用。我们一直在用两种ascoglossan海蛞蝓Elysia chlorotica和Elysia crispata来研究这种关联。利用药理学和分子技术，我们发现至少有一种叶绿体蛋白，岩藻黄素-叶绿素结合蛋白（FCP）是合成的，而质体驻留在鼻涕虫细胞的细胞质中，我们已经发现了FCP基因序列在鼻涕虫基因组DNA中使用南方印迹分析。我们还发现了其他几种质体蛋白的类似证据。这些发现使我们产生了一种假设，即编码叶绿体蛋白质的基因已经从藻类转移到动物细胞基因组中。如果这一假设是正确的，那么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，海蛞蝓将为确定多细胞生物之间功能基因转移的机制以及解释细胞器的内共生起源提供一个很好的模型系统。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质体-鼻涕虫关联的分子和细胞生物学性质。两种蛞蝓之间的比较应该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.