> In these gene modification treatments, what genes are being modified?  
> The genes in some cells, or all cells?  If only some cells, how are the treatments targeted? 

RNA has many roles in cell development so there is no one answer. It can be used to challenge the immune system, producing a robust immune response, somewhat like a vaccine. 

It can be used to switch genes on and off in the target organism, either as exploration to see what genes do, or as a tool for pest control, as we have discussed. In this mode, genomic material should not be affected, at least not the host DNA. Although, gene silencing appears to be heritable, hence termed epigenetic inheritance. 

Finally, this new work shows that using RNA, one can actually make edits to the genome directly, changes which would be passed on to the next generation of cells. In this way one could target individual cells which are defective, as in congenital birth defects, which would enable the cells to start producing "normal" cells instead of the bad version. This type of cell targeting is in its infancy.

People who do genetic engineering already have techniques to edit the genomic material inside germline cells (sperm, eggs). This is how transgenic animals are produced. However, it is fairly tedious and a bit hit or miss. Nevertheless, one can design synthetic DNA sequences (like the gene for fluorescence, for example) and insert them into developing animal eggs. The eggs go on to become transgenic animals, like mice or fish. In this case, they would glow under black light. 

Fluorescent proteins are not just a gimmick but they can be used to accompany other genetic material and therefore used as a marker to see that the genes are successfully incorporated into the next generation, and more importantly, they can show visually the function of genes and their products. 

What is new in the work I just posted, is that one can bypass some of the techniques used now, to the much simpler approach of using RNA to go directly into the cell, whether its a defective blood cell (somatic cells) or a living egg (germline cells) and make changes. Hence, the idea of using it as a treatment for illness, a pest control device (which could shut down important cell functions in the pest) or to make actual heritable changes.

Actual heritable changes could include: pre-emptively repair defective genes leading to birth defects; produce novel plants and organisms (genetic engineering); target pest reproductive systems to create non-viable offspring. These all require the careful identification of "genes" or coding that has clear function, and extensive experimentation to determine the effectiveness and safety of the technique. 

All of us working with genomic experiments are cognizant of the potentials for good and bad, and the whole field is extremely well regulated and monitored. No genetically modified material is allowed to be released into the environment without ample justification and reasonable consideration of the safety and impact. Of course, there are those who cannot believe that genetic engineering is safe. 

Pete

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