Biologists and geneticists know that a very convenient way to study functions of certain mammal genes, including their role in developmental disorders, is by means of introduction of these genes into embryos of laboratory animals. Russian scientists from St. Petersburg State University, Research and Development Centre of Experimental Medicine Russian academy of medical sciences), and the Institute of High-Molecular Compounds (Russian academy of sciences) suggest their own technique for this purpose. Researchers injected DNA-protein complexes to pregnant mice, and genes were able to cross placental barrier and then could be detected in embryo’s tissues.

Currently most common technique for gene transfer is using modified viruses; however, introduction of a virus in an organism can be toxic and often causes active response of organism’s immune system. Non-viral DNA delivery methods don’t have mentioned drawbacks, and researchers prefer to use them despite the fact they are much less effective. One of these techniques is called intravenous hydrodynamic DNA injection. The idea is that DNA together with a large amount of solvent is quickly (in several seconds) introduced into blood flow of a mouse. Hydrodynamic strain helps DNA squeeze through a transplacental barrier and enter tissues of an embryo, which cannot be reached by means of an ordinary intravenous injection.

 

 

In the experiments scientists used DNA of a gene, coding luciferase, a glowing protein, belonging to fireflies. This DNA was bound to a synthetic peptide, a short polymer of amino acids linked by peptide bonds. Part of this peptide was designed to bind with DNA and, at the same time, work as an “access pass” to a cell nucleus. Another part of the peptide showed affinity to cells of a placental trophoblast. Thus, DNA, which is bound to a hybrid peptide flows it everywhere, like a thread follows needle, first to cells of a placenta, later this complex moves to embryo’s tissues, and finally reaches cell nucleus, where genes are usually located.

A complex molecule, consisting of DNA of a luciferase gene and a hybrid peptide, was introduced into caudal (tail) vein of pregnant female mice by means of hydrodynamic DNA injection. This DNA was mainly traced in animals’ liver, but some of it got into embryos, and into all tissues. This experiment shows that placenta can be penetrated by alien DNA, introduced by means of a hydrodynamic injection. Researchers plan to make their development more effective, and to transfer genes into embryonic tissues via either some specific agents, which promote gene transplantation, or by injecting DNA somewhere else, into peritoneum, for instance.

Researchers describe their new development as a simple, cost-effective technique, which causes no immune response in pregnant female mice, and that is why multiple injections can be made, when necessary. This technique can become a good basis for precise delivery of required genes into mammalian embryos’ tissues.

Source: Science News

Kizilova Anna