Figure 10

Stages of vertebrate pancreas evolution. The earliest vertebrates likely possessed diffuse islet organs associated with the bile duct as found in extant jawless fish lineages such as hagfish and lampreys. The development of a distinct pancreatic gland with endocrine (insulin, glucagon and somatostatin) and exocrine (digestive) functions is a jawed vertebrate innovation and only coelacanths and tetrapods possess a four hormone (insulin, glucagon, somatostatin and pancreatic polypeptide (PP)) organ. Many of the key genes in jawed vertebrate pancreas development and function are members of multi-gene families, produced during the two rounds of whole genome duplication that took place early in vertebrate evolution.