Studying the genetics of cancer often involves looking specifically at cancerous cells (that is, tumor cells) and asking what is different about those cells than the regular cells they were before.

For example, what mutations are present in the DNA of a cancer cell, that could be the cause of the cancer? Also… different genes could be transcribed (read active) in cancer cells, or perhaps the same genes are active but more or less than normal. What are those genes? Answering these questions helps scientists in two ways. First, it allows them to understand the actual workings of cancer- what causes cancer? Second, it provides diagnostic ques- if we know something is only found in cancer cells, then we know how to find cancer (and also what type it is).

That’s where cancer-specific transcripts come in.

Transcripts are the mRNA that is produced from a gene. So what is a chimeric transcript?

Normally, a transcript comes from a single gene. But a chimeric transcript, just like the mythical animals, is made up of more than one gene. There are a few genes which do this as part of their normal function, but there’s another way these transcripts are made, that is not normal.

About 17% of our genome is made up of a sequence called LINE (which stands for Long Interspersed Nucleotide Elements, or L1). These are stretches of DNA which, when “activated” can insert themselves into another place in the genome, sometimes directly in the middle of another gene, or in the vicinity of a gene. That can have serious consequences because it disrupts the natural function of those genes, so normally L1 elements are silenced, they are not jumping around, except as a recent paper shows, in some cancer cells.

It turns out that not only are these fragments of DNA inserting themselves into other genes, but they are creating chimeras: Transcripts with the normal gene and L1 DNA that are not found in normal cells.

For further discussion on this paper check out Scientific Blogging.

Image: Frank Chimero via Flickr

Citation:

Cruickshanks, H., & Tufarelli, C. (2009). Isolation of cancer-specific chimeric transcripts induced by hypomethylation of the LINE-1 antisense promoter Genomics, 94 (6), 397-406 DOI: 10.1016/j.ygeno.2009.08.013