While we’re on the subject of extinct species, Prof Kevin Campbell and colleagues in Canada and Australia have reported resurrecting mammoth hemoglobin in a paper out this week in Nature Genetics. This won’t help at all with cloning a mammoth, but provides a fascinating insight into mammoth physiology and evolution.
Hemoglobin is the protein which transports oxygen in the blood. It is made up of two subunits, alpha and beta globin, which are coded for by two different genes. Campbell and colleagues used fairly basic molecular biology techniques to isolate these genes from mammoth remains and express the protein in bacterial cells. Firstly, they amplified both elephant and mammoth hemoglobin genes using PCR and compared their sequences, finding that mammoth beta-globin protein differs from the elephant protein at three amino acid sites.
They then inserted the elephant hemoglobin genes into a bacterial carrier molecule called a plasmid, which had previously been designed to express human hemoglobin. This carrier molecule basically contains the elephant hemoglobin genes and a bacterial promoter – a little sequence of DNA which is recognized by bacterial proteins that switch on the genes to produce the hemoglobin protein. Producing mammoth hemoglobin was slightly more complicated because the mammoth DNA was degraded so the hemoglobin genes had to be isolated in pieces. This meant they couldn’t insert the genes directly into the plasmid, so instead they recreated the mammoth sequence by modifying the elephant construct at the sites where it differs from mammoths.
Once they had the expressed hemoglobin, they then compared the oxygen-binding properties of the elephant and mammoth proteins using standard physiological tests and chemical modelling. The changes in the amino acid sequence of the mammoth hemoglobin protein, when compared with elephants, appear to be important for cold tolerance, as they allow the mammoth blood to deliver oxygen to cells even at very low temperatures.
“This is true paleobiology, as we can study and measure how these animals functioned as if they were alive today” says Professor Alan Cooper, Director of the Australian Centre for Ancient DNA (ACAD) at the University of Adelaide, where the mammoth hemoglobin sequences were determined. You can hear more about this research from Alan Cooper on Radio New Zealand here.
Reference: Campbell KL, Roberts JEE, Watson LN, et al. Substitutions in woolly mammoth hemoglobin confer biochemical properties adaptive for cold tolerance. Nature Genetics doi:10.1038/ng.574