Dr. Orias earned his Ph.D. in Zoology in 1960 at the University of Michigan where he studied mating type differentiation in Tetrahymena. In 1974-75 he was Guest Professor at the Biological Institute of the Carlsberg Foundation in Copenhagen, Denmark. During 1979-80 he was a Visiting Professor in the Anatomy Department at the Albert Einstein College of Medicine. He was a member of the Genetics Study Section of NIH from 1977-1981, and of the Editorial Board of the Journal of Protozoology. Dr. Orias was a co-organizer of the 2nd International Ciliate Molecular Genetics meeting held here at UCSB in July 1986. Dr. Orias joined the faculty at UCSB in 1959.
We do molecular and developmental genetics of the unicellular eukaryote Tetrahymena thermophila. We have been mainly working on two problems: the mechanism of mating type determination, and the construction of a genetic map of the Tetrahymena genome. In conjunction with the Wilson laboratory at UCSB, we are also investigating an unusual microtubule structure that is required for cell-to-cell transfer of gamete pronuclei during fertilization in conjugating Tetrahymena.
The Ciliated Protozoa (the phylogenetic group to which Tetrahymena belongs) share a unique feature: the possession of a polyploid somatic nucleus (the macronucleus or MAC), which is autonomous from the diploid germline nucleus (the micronucleus or MIC). The MAC differentiates from the MIC after fertilization; this differentiation is accompanied by an extensive occurrence of specific DNA rearrangements. Clonally inherited, developmentally programmed differentiations of the MAC play a crucial role in both classes of phenomena under study in my lab. Tetrahymena has a number of attractive features that allow one to combine molecular biology with conventional genetics (see Tetrahymena genetics page).
Mating type determination. Previous work by Nanney et al. had shown that the germline (MIC) encodes the genetic potential for 7 mating types. Yet any one vegetative cell line expresses only one of these mating types, stochastically determined during MAC differentiation. Many features of this phenomenon, elucidated by genetic experiments, make it appear very possible that programmed DNA alternations during MAC differentiation play an important role in this process. Our genetic work leads us to the hypothesis that during MAC differentiation, the locus of mating type determination can undergo a series of switches through a well defined series of hereditary mating type states. A stochastic event, perhaps related to amplification to final ploidy, stops the differentiation process at an unpredictable state along the series. We are currently attempting to clone the locus of mating type determination, as a first step towards ultimately reaching a molecular understanding of this interesting phenomenon.
Mapping the genome. We are mapping the Tetrahymena thermophila genome using random PCR-amplified DNA polymorphisms. To date, nearly 500 DNA polymorphisms have been assigned to arms of the 5 germline chromosomes; nearly 400 of those have been placed in 25 linkage groups, at LOD>3 statistical significance. These linkage groups also include some of the classical Tetrahymena loci. The immediate goal is to identify and map 500 DNA polymorphisms, so that any new mutation or cloned gene should have at least 95% probability of showing linkage to an already mapped genetic marker.
Site-specific fragmentation of the micronuclear form of the DNA during macronuclear differentiation yields 200-300 autonomously replicating molecular species. These pieces lack centromeres and are randomly distributed during macronuclear (amitotic) division. We have recently been able to identify loci that are located on the same piece of macronuclear DNA, based on their co-assortment during division in doubly heterozygous macronuclei. A genetic mapping of the fragmented macronuclear genome is now underway.
SELECTED REFERENCES:
Orias E. and Bradshaw A.D. (1992) Stochastic developmental variation in the ratio of allelic rDNAs among newly differentiated, heterozygous macronuclei of Tetrahymena thermophila. Devel. Genet. 13: 87-93.
Lynch T.J., Brickner, J.H., Nakano K.J. and Orias E. (1995) Genetic map of randomly amplified DNA polymorphisms closely linked to the mating type locus of Tetrahymena thermophila. Genetics 141: 1315-1325.
Longcor M.A., Wickert S.A., Chau M.-F. and Orias E. (1996) Coassortment of genetic loci during macronuclear division in Tetrahymena thermophila. Eur. J. Protistol 32: 85-89.
Orias E.(1997) Tetrahymena Genome Project Web Page. Adress: http://lifesci.ucsb.edu/~genome/Tetrahymena.
February 16, 1997
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