|Scientists reveal general picture about the origin of new genes in fruit flies
|Gene, the very basic unit of life, has long held the limelight in modern biological studies. One fundamental truth revealed by scientists of the twentieth century is that gene is a segment of DNA and provides information an organism needs to build or do something -- like making a nose or an arm, or repairing a wound. Now, with the help of molecular biology, scholars are able to think about another important issue: where do the new genes come from?
Like doctors infer an individual's growth from the embryo, geneticists find sufficiently young genes to observe their origination and evolution, through which they might finally peep into the rise of all genes, including ancient ones that have undergone millions of years of variation.
Since 2004, Dr. WANG Wen and coworkers with the CAS-Max-Planck Junior Research Group on Evolutionary Genomics have reported a series of young genes of Drosophila (or fruit fly, a two-winged insect model often used in genetic experiments), such as the monkey-king which bares out gene-splitting mechanism and the testes-specific expression Hun, etc.
Based on extensive genome sequence comparisons among 300-odd young genes in Drosophila melanogaster species subgroups, PhD candidates ZHOU Qi, ZHANG Guojie et al from Wang's group recently surveyed the mutational process by which new genes originate. Although previous case studies had explained some general principles governing the origination of new genes, this is the first whole-genome level investigation by far which provides a panoramic picture for the origin of new genes in fruit flies.
Several interesting observations were made. First of all, as gene duplication is widely believed to play a pivotal role in evolution, Wang and collaborators discovered that within a single species ¨C melanogaster for instance ¨C newly-born genes are largely tandem duplicates, while survived old genes shared by multiple species are usually dispersed duplicates.
Then, researchers identified the previously underestimated roles of de novo origination and retroposition. The process by which a new gene is de novo generated from non-coding sequence, a less discussed topic before, proves responsible for over one tenth of the birth of new genes. And retroposition, a means of gene copying which features the integration of a sequence derived from RNA into a DNA genome, is considered a major mechanism that generates about another one tenth of new genes.
Their study also supported a widespread contribution of changes in gene structure to fixing new genes. About 30% of the identified new fruit fly genes recruit various genome sequences and form chimeric gene structures.
According to Dr. Wang, the origination of new genes is a key mechanism underlying the emergence of genetic novelties during an organism's evolution. Known processes of new gene's creation include exon shuffling, gene duplication, retroposition, gene fusion, fission, de novo origination and so on. The origination rate is around five to 11 new genes per million years.
However, Wang says that scientists still need to work out more genome sequences in other species to testify similar patterns, and the studies on how new genes impact the development, heredity and evolution of organisms are equally significant.
The work, published by Genome Research, is co-funded by a CAS-MPS Fellowship, the National Natural Science Foundation of China and the National Basic Research Program of China.
Dr. Wang was recruited in 2002 to the CAS Kunming Institute of Zoology as head of the Group. He also serves the Institute's deputy director.
Some of Wang's work is joined by overseas researchers, including Prof. Manyuan Long from the University of Chicago, who discovered Jingwei, the first gene of sufficiently recent origin in Drosophila to offer insights into the origin of a gene.