As a general rule, genes and transcribed into RNA, a copy of the genetic code that is translated into protein. However the RNA transcript itself can have its genetic code edited before being translated into protein, providing a way to make different versions of a protein. In humans RNA editing seems to happen more in nervous system gene transcripts and abnormal RNA editing is frequently detected in neurological disease.
Squid has long been a model system to study how nerves transmit signals, due to their extremely large nerves but genomic information is not yet available for this model organism. However researchers from Tel Aviv University took advantage of advances in DNA sequencing and computational analyses and have investingated RNA editing in the squid Doryteuthis pealieii. While RNA editing is rare in mammals and fruit flies, squid seem to use RNA editing much more frequently. In terms of the types of RNA transcripts that are edited, changes to the genetic code were more common in RNA transcripts associated with brain physiology, which is consistent with other organisms that have been looked at including humans.
The researchers extracted DNA and RNA from a squid. The RNA and genomic DNA sequences were compared. Places where the RNA did not match with the genomic DNA were identified as edited sites. 60% of the RNA transcripts were edited, whereas the fruit fly was previously reported to edit only 3% of transcripts and mammals even less. Why so much editing in squid? It is not clear but researchers suggest that RNA editing could be related to the sophistication of their complex nervous system and behaviors compared with their cousins, clams and oysters. Research in fruit flies and octopus point to RNA editing as a quick way to produce different proteins adapted to a particular temperature or environment.
The majority of transcripts in the squid nervous system are extensively recoded by A-to-I RNA editing. Alon, S., et al. eLIFE 2015; DOI: 10.7554/eLife.05198.