Transferred genes and endosymbiosis

转移基因和内共生Sidney K Pierce南佛罗里达大学在两种生物体之间成功转移功能基因是基因转移治疗的目标，也是遗传修饰技术的基础。 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物化学进化的主要力量。基因转移的研究包括试图插入正确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、牲畜或细胞培养物的特定特征。 大部分研究涉及将感兴趣的基因机械转移到宿主细胞中，但最近已经开发了使用病毒载体的转移。 在真核系统中，大多数研究都集中在含有细胞器的DNA与核基因组之间的基因转移机制，特别是高等植物中来自线粒体的基因转移。 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很少。 迄今为止，几乎所有的信息都来自于至少有一种生物是原核生物的转移研究。 发现基因成功转移的机制，以及外源基因在宿主细胞中的整合和表达，对于理解整个过程和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。研究人员似乎已经发现了两个案例，其中功能基因在两个真核生物界的两个生物体之间转移。 此外，可疑基因被传递到宿主细胞谱系中的后代。 这一发现来自于对叶绿体共生的长期研究，这是一种有趣的现象，通常来自特定物种的叶绿体被动物（或原生生物）细胞吞噬，并继续在宿主细胞内进行光合作用一段时间。 我们一直在调查这样一个协会使用两个物种的ascoglossan海蛞蝓Elysia chlorotica和Elysia crispata。使用药理学和分子技术，我们已经表明，至少有一个叶绿体蛋白，岩藻黄质叶绿素结合蛋白（FCP）的合成，而质体驻留在蛞蝓细胞的细胞质中，我们已经发现蛞蝓基因组DNA中的FCP基因序列，使用Southern印迹分析。 我们还为其他几种质体蛋白质提供了类似的证据。 这些发现使我们提出了一个假设，即编码叶绿体蛋白的基因已经从叶绿体转移到动物细胞基因组中。 如果假设是正确的，多细胞物种之间的基因传递可能是一个重要的进化机制，海蛞蝓将提供一个很好的模型系统，用于确定多细胞生物之间功能基因传递的机制，以及解释细胞器的内共生起源。 因此，这个提议的具体目标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。 我们的实验将依赖于分子生物学和电子显微镜的分辨能力，以确定质体-蛞蝓缔合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.