Protozoan Sequencing Added to U.S. Genome Project

By GAIL GALLESSICH BROWN

A protozoan that has been studied by a UC Santa Barbara scientist for the past 46 years has been assigned high priority for genome sequencing by the National Human Genome Research Institute (NHGRI).

Called Tetrahymena thermophila, the single-celled organism split off from an ancestor in common with humans about two billion years ago. Yet it carries many of the same genes as humans, and can be used to understand the function of many human genes.

Small as it is, Tetrahymena has about 30,000 genes, a similar number as humans. It reproduces quickly, doubling in numbers every two hours, which makes it inexpensive and easy to study. The organism is a ciliate, and uses tiny, hair-like cilia to propel it.

Eduardo Orias, research professor of genomics in the Molecular, Cellular, and Developmental Biology Department, nominated the protozoan for sequencing by submitting a white paper to the NHGRI on behalf of and with contributions from the international ciliate research community. He also consulted with the Whitehead Institute/MIT Genome Center. (The paper is available on line at http://www.nhgri.nih.gov/DER/Sequencing/Tetrahymena_Genome.pdf). This resulted in Tetrahymena being chosen as a high priority genome for sequencing.

Orias, who is the coordinator of the International Tetrahymena Genome Project, will collaborate in the analysis of the genome sequence and will facilitate the exchange of information and expert advice between the Tetrahymena research com munity and the sequencing center. His lab at UCSB will provide Tetrahymena DNA for the genome sequencing. "My lab is one of the largest repositories for the many strains of Tetrahymena that exist," he said.

He began to study Tetrahymena in 1956 when he was a graduate student at the University of Michigan, and has been working on it virtually ever since. For several years his research group at UCSB has been doing genetic and physical mapping of the organism, and making samples of the strains available to other investigators.

Sequencing of Tetrahymena will have many benefits, Orias suggested, including in forming the biology of the causative agent of malaria and other related protist pathogens of great medical or agricultural significance.

Studies of Tetrahymena have made major contributions to genetics and cell biology. For example, scientists used this organism to study the structure of telomeres (ends of chromosomes) and the telomerase enzyme, which has profound importance in cancer and aging.

Rat and mouse genome sequencing is approaching completion. In addition to Tetrahymena, NHGRI has chosen (in alphabetical order) chicken, chimpanzee, fungi (various species), honeybee, and sea urchin for the next round of sequencing.