Gene transfer refers to the artificial or natural transfer of foreign genetic material to a fertilized egg. More precisely, individual genes are transferred from a donor organism to a recipient organism. A distinction is made between horizontal and vertical gene transfer. Gene transfer can take place by transformation, conjugation or transfection. Technical methods are, for example, microinjection or the biolistic method, also called “gene gun”.
What is gene transfer?
Gene transfer refers to the artificial or natural transfer of foreign genetic material to a fertilized egg. Horizontal gene transfer is a process in which genetic material is taken up or passed on without sexual reproductive pathways and regardless of species boundaries. In this process, a gene with a specific property is introduced into a genome and activated there. More precisely, this means that genetic material is not transferred along a lineage, whereas vertical gene transfer occurs through ancestors to descendants. In evolutionary theory, horizontal gene transfer provides an explanation for the emergence of microorganisms, for example, which are characterized by strong evolutionary leaps. Vertical transmission, in which pathogens are passed on to another generation via the genetic material of an infected generation, must be distinguished from this as a special form. In microorganisms and invertebrates, horizontal transfer is documented. Among bacteria, for example, genes that are resistant to antibiotics spread. In Wolbachia bacteria, on the other hand, an entire genome is transferred into the cells of a fruit fly, even if only some of the genes later take over certain functions. Due to the rapid decomposition of tansgenic DNA outside a cell, horizontal gene transfer is unlikely to occur in microbiological fauna. Mostly it takes place in the laboratory. However, the emergence of various resistances and pathogens alone could provide information about a naturally occurring gene transfer. Such gene transfer has been demonstrated, for example, in the soil bacterium Agrobacterium tumefaciens, which has the ability to transfer DNA to plant cells, a process first described by the Belgian molecular biologists Marc Van Montagu and Jozef Schell in 1983, and in the Gram-negative rod bacterium Bartonella henselae, which is able to transfer DNA into eukaryotic cells via its own transport system. Vertical gene transfer, in turn, is a crossing that takes place between two individuals or plants on a sexual basis, whereby genes are passed on to the next generations. We are then talking about transmission along the vertical lineage. For example, if transgenic and non-transgenic plants are crossed, the non-transgenic ones also pick up the constructs of the genes. Likewise, it can be a matter of passing on to chromosomes that have gene defects. In microorganisms, the inheritance of DNA to offspring is called vertical transmission. This term, in turn, additionally describes the transmission of pathogens during pregnancy, birth process and after birth by the mother to the child. Infectious diseases can occur here, e.g. rubella or HIV.
Function and task
In genetic engineering, horizontal gene transfer is used to create genetically modified organisms. The process involves numerous methods depending on the particular modification, such as whether it is a prokaryote or eukaryote. The former refers to organisms that do not have a cell nucleus. These are e.g. bacteria, more precisely eubacteria and archaebacteria. They are characterized by a high biological adaptability and a simple morphology, have no mitochondria, a genome free in the cytoplasm, have a complex extracellular matrix and additional DNA. Accordingly, eukaryotes are organisms that have a nucleus and develop from nucleus-containing initial cells. These, in turn, may be spores or zygotes. A zygote is a diploid cell that has arisen from an egg and sperm cell. Spores are unicellular or multicellular microorganisms with a high resistance to environmental influences. In prokaryotes, transformation, transduction, and conjugation occur; in eukaryotes, transfection occurs. In transduction, DNA fragments are transferred between two bacteria by infection with bacteriophages.In conjugation, DNA is transferred from one bacterium to another. Even from donor to recipient across species boundaries. Bacteria that act as donors have the F factor that makes conjugation possible in the first place. Using a plasma bridge, a connection is created between the bacteria and the donor transfers the plasmid to the recipient. Transformation, in turn, is the uptake of free DNA by bacteria.
Diseases and disorders
Researchers have now been able to demonstrate that human genetic material was not only transferred from one generation to the next via vertical gene transfer, but that humans also adopted it from bacteria during evolution. Thus, more than a hundred genes from microorganisms entered the human genome via horizontal gene transfer. The result of the research first caused a stir in 2001, but was still considered controversial. As the years progressed, a more extensive genome database finally became available, and British scientists compared genes from fruit fly species, primates, various nematodes and humans with hereditary material from the microorganisms. In the case of humans, the result was 145 genes that originated in the microbial world and that also perform important functions, such as being involved in fat metabolism or in various immune reactions. Such a horizontal gene transfer probably occurred at a time when the different species had not yet split up. In contrast, in nematodes and fruit flies, gene transfer in this form still exists today. However, it has not yet been possible to clarify how the smuggling of such bacteria into the human genome took place. One possible explanation is viruses, which could have served as transporters. In general, gene transfer can have both a positive effect on the health of organisms by making them immune to external susceptibilities, but the opposite can also occur whereby pathogens, as in the case of HIV, are passed on to another organism.
