By Raman Sukumar & group (IISc), Sanjeev Galande & group (IISER)
For several years, there has been a global effort to sequence the genomes of numerous plants and animals. A few years ago, the genome of the African elephant was sequenced. Two years ago, we at the IISc and IISER began work on genome sequencing of the Asian elephant, the species that is found in India, as well as in many countries in south and south-east Asia.
The elephant is the largest living land mammal in the world, and traces its ancestry to the African subcontinent where the ancestors of both the Asian and African elephant evolved. The Asian elephant lineage is believed to have travelled into Eurasia several million years ago while the African elephants remained restricted to Africa.
The Asian elephant is one of the focus areas of our research group at the Centre for Ecological Sciences at IISc. When we started, the genome of the Asian elephant had not been sequenced. Besides building this genetic resource, our effort was to find the genetic differences between the Asian elephant and their cousins in Africa, and also between elephants and other mammals.
Another group in the US was working on sequencing the genome of the Asian elephant and it was able to complete its project earlier this year. Nevertheless, we continued our work, and though some data, relating to the overall genome sequence, for example, is likely to be the same, our project has thrown up some new and interesting facts.
For the purpose of our research, we extracted the DNA from the blood sample of an elephant named Jayaprakash in the Bandipur elephant camp in Karnataka. After sequencing its genome, we compared it with the genome of the African elephant which is already available in a public database.
Our results show that there are about 1,500 genes in the Asian elephants with sequences that are different from their African cousins. Many of these genes are responsible for sense of smell. This is expected as the ancestors of present-day Asian elephants moved from the plains of Africa into Eurasia and finally to Asia, they would have encountered
different smells and would have adapted to respond to it differently. Our study provides a strong evidence of a genetic basis for the differences between the Asian and African elephants in their sense of smell.
The other observation was the kind of genes that were getting ‘expressed’ in the blood cells of elephants. While every cell of a species has the same genome sequence, certain genes get expressed in different ways across organs or tissues. This enables an organ or tissue to carry out its specific functions. The part of the genome that is expressed in a particular tissue or organ is called its transcriptome. We sequenced the transcriptome of the blood cells of an Asian elephants and compared it with other well-studied animals. We found that many of the genes known to be important for immune system function in other animals are also expressed in the Asian elephant, but some of the genes were uniquely expressed only in the Asian elephant blood.
Our research has also built up a genetic resource which can be used as primary data for further studies. The genetic information will help other researchers undertake new projects in many areas of research such as evolution, genetic disorders, physiology, metabolism, etc.