Answers to submitted questions will be answered and updated hopefully on a weekly basis. Dave will try his hardest to answer in a timely manner. Some responses may answer multiple questions that I grouped together. Check out what other people have asked first! Your burning question might have already been answered! ---Science Penpals

1. Does a DNA strand need all of its components to be active?  (Elias, New Mexico)

DNA is one incredibly complex set of instructions, so it's a great question to ask how much of it is actually needed to work.  Many research teams all over the world are working very hard to answer this very question.  The answer seems to be it depends.  Some parts of your DNA are necessary for your cells to live or behave correctly, and any changes to them are very dangerous.  On the other hand, we don't know the function of some parts of your DNA, and changes to them don't have much effect on your cells.  So it depends on which parts of the DNA you may be missing.

Genes are simply sections of your DNA– about 2% of your genome is made of genes.  These genes are scattered around the genome, and they are the instructions for your cells to make the protein molecules they need to live and do things.  Through studying the differences in the DNA between people, researchers have found that many people have sections of their DNA that are missing or are actually duplicated and present in multiple copies.  If these deletions or duplications overlap genes, there is a good chance this person's cells can't work right, which can lead to a variety of diseases.  For example, most cases of Duchenne muscular dystrophy and cystic fibrosis are known to be caused by specific deletions within important genes.  But not all deletions turn out to be bad.  Other research has found that there are over 100 genes can be entirely deleted without causing disease.  And one cool study showed that some deletions in early humans may have helped humans grow larger brains than our chimpanzee cousins!

 
 

2. Can you use CRISPR to remove T cells from the human genome?  Could that be harmful?  (Suhani, North Carolina)

At the moment, using CRISPR to eliminate T cells in humans isn’t possible for a few reasons.

 

First, editing every cell of a particular type, like T cells, would probably have to be done at the embryo stage, when there are only a few cells.  That way, most or all cells in the body would take on the mutations introduced at this early stage.  Editing human embryos is a big no-no right now, though.  In the US, the FDA and NIH are legally blocked from approving or funding embryo editing for clinical use.  However, it was reported last year that a researcher in China edited human embryos, which became twin girls.  The scientific community and world governments (including China) have come out against such a practice, so practically, you’re not allowed to do this kind of thing in humans yet.

 

Secondly, T cells are really, really important.  Most of your white blood cells are T cells.  You don’t want to get rid of them.  Their job is to both fight invading pathogens and signal other immune cells to fight the invaders.  People are sometimes born with mutations that stop their T cells from functioning, and without receiving a bone marrow transplant to give them a whole new immune system, these patients aren’t able to fight infections and most likely die very early.

A nude mouse is a strain of lab mouse without T cells.  They have a mutation in the FOXN1 gene, resulting in a lack of thymus (where T cells are made) and no hair!

Photo: Armin Kübelbeck

All that aside, it is possible to eliminate certain types of cells in the body.  This is commonly done in mice and rats if scientists want to study what a particular type of cell does, or if we want to study the development of cancer by getting rid of the immune system.  CRISPR can be used to knock out particular genes crucial for T cell development by introducing mutations that stop these genes from working.  No T cell genes, no T cells.  It is also possible to use CRISPR to insert a kill-switch that kills a particular type of cell during development.  This can be done by cutting the DNA and inserting a new gene that makes a toxin with an extra signal that only allows the toxin to be made in T cells.  Both of these methods would involve editing the genomes of early embryos so that every cell gets the edit.  These mice/rats can grow up without T cells, but they must be raised in a sterile environment where they can avoid infections (similar to a human without T cells).

 
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