I am new guy working on C.elegans. Now, I will have to inject my GFP tagged construct together with WT-unc as rescue to unc worms. Basically, for what I know so far, after microinjection, in the rescued worms, my construct will be in the outside of the genome (not insert into chromosome) in the form of extrachromosomal array. But, I still do not quite understand what does extrachromosomal array mean? How will they work if they are not in the chromosome? Could anyone explain this important term to me? Thank you so much!
When you inject a gene of interest (in your case its GFP construct) along with selection marker (wild type unc-119?) a weird thing happens in C. elegans. These two plasmids are randomly chopped and joined together to generate an ‘extrachromosomal array’. Imagine these two plasmids are like two types of circular ropes; once inside the C. elegans body, these two types of ropes are randomly chopped and the resultant linear ropes are knotted together to create a large rope (the word ‘array’ indicates just this. ).
A couple of notes to Guna’s reply:
Do notice the part where Guna ways the plasmids are randomly chopped up, because if you take their metaphor about ropes being knotted together too literally, you could be misled. As I understand it, the structure of the array is a very large number of fragments of the DNA you injected fused together as a single DNA molecule. In theory, this means that control elements present on one plasmid could be placed next to reporter constructs from another plasmid; in practice, I’m not sure I can recall hearing of this possibility causing problems. Although it is not necessary to linearize your plasmids to get them incorporated into transgenes in C. elegans, some people prefer to do so in the hope that they can thus affect in what conformations the constructs are fused together, and avoid this possiblity. People also dilute their transgenes with carrier DNA, which can increase transmission frequency and reduce the probability of transgene fragments appearing net to each other.
“Extra” in the context of “Extrachromosomal” does not mean “additional”, it means “outside”. The extrachromosomal array is subject to mitotic loss and is not considered to behave like an additional chromosome.
The WormBook chapter is far more focused on explaining the procedures and the options than in describing just what you will end up with after having followed all the excellent advice it offers, but if you start there and look at some of the references it cites you should be able to figure out what you want to know about C. elegans transgenes.