Initially, the only way to obtain insulin for clinical use was to extract it from the pancreas of another creature. Animal glands were obtainable as a waste product of the meatpacking industry. Insulin was derived primarily from cows (Eli Lilly and Company) and pigs (Nordisk Insulinlaboratorium). The making of eight ounces of purified insulin could require as much as two tons of pig parts. Insulin from these sources is effective in humans as it is highly similar to human insulin (three amino acid difference in bovine insulin, one amino acid difference in porcine). Initially, lower preparation purity resulted in allergic reactions to the presence of non-insulin substances. Purity has improved steadily since the 1920s ultimately reaching purity of 99% by the mid-1970s thanks to high-pressure liquid chromatography (HPLC) methods. Minor allergic reactions still occur occasionally, even to synthetic "human" insulin varieties.Beginning in 1982, biosynthetic "human" insulin has been manufactured for clinical use through genetic engineering techniques using recombinant DNA technology. Genentech developed the technique used to produce the first such insulin, Humulin, but did not commercially market the product themselves. Eli Lilly marketed Humulin in 1982. Humulin was the first medication produced using modern genetic engineering techniques in which actual human DNA is inserted into a host cell (E. coli in this case). The host cells are then allowed to grow and reproduce normally, and due to the inserted human DNA, they produce a synthetic version of human insulin. Manufacturers claim this reduces the presence of many impurities.
The cellular function that links them is a common signalling pathway that brings information from outside the cell to the nucleus. This pathway is called the Ras-MAP-kinase signal transduction pathway (Ras-MAPK Pathway). References
Some text in this article was originally taken from http://ghr.nlm.nih.gov/condition=costellosyndrome, a public domain source

External links

GeneReviews: Costello Syndrome
GeneReviews: Daisys battle with Costello Syndrome