Studies on the evolution of biological processes in vertebrates have historically been hindered by a lack of genetic information of different species. Previous studies often relied on morphological traits to attempt to reconstruct the evolutionary pathways of modern vertebrates. With the availability of more and more genetic data for a range of species, it has been possible to perform more accurate assessments of vertebrate evolution.
We already know that certain vertebrate biological processes - such as parts of our immune system - may have had their initial origins in cartilaginous fish (see The Shark Post - 29th Jan) so it is no surprise to learn that we may owe our pancreatic system to sharks too.
The researchers examined transcripts encoding genes involved in insulin regulation, glucose sensing, digestion, transcriptional regulation and other processes and compared them to transcripts in mammalian lineages. The researchers found that the mechanisms responsible for glucose sensing and insulin regulation are very similar across the vertebrate lineage. These features are therefore hypothesised to be commonly shared across all jawed vertebrates. Going one step further, the researchers propose that these shared mechanisms may have led to the development of the complex, glucose dependant brain of vertebrates.
Whilst the pancreas of elasmobranchs does differ to that of other fish and tetrapods in that the elasmobranch pancreas is a 3 peptide system and "higher" vertebrates have a 4 peptide system, the elasmobranch pancreas shares similarities to the mammalian pancreas as it is a distinct gland which has both endocrine and exocrine functions. These factors support the idea that the vertebrate pancreas evolved from a single, early origin and was possibly heavily blueprinted on the early shark pancreas.
Whilst this work has not yet been published, it may be viewed on bioRxiv here http://biorxiv.org/content/biorxiv/early/2014/06/06/006056.full.pdf
Mulley, J., Hargreaves, A., Hegarty, M., Heller, R. and Swain, M. (2014) Transcriptomic analysis of the lesser spotted catshark (Scyliorhinus canicula) pancreas, liver and brain reveals molecular level conservation of vertebrate pancreas function.
