Transferred genes and endosymbiosis

University Of South Florida, Tampa FL

Investigators

Abstract

Transferred genes and endosymbiosis Sidney K Pierce University of South Florida The 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.