[4][page needed] As a ciliated protozoan, Tetrahymena thermophila exhibits nuclear dimorphism: two types of cell nuclei.

They have a bigger, non-germline macronucleus and a small, germline micronucleus in each cell at the same time and these two carry out different functions with distinct cytological and biological properties.

This unique versatility allows scientists to use Tetrahymena to identify several key factors regarding gene expression and genome integrity.

Because Tetrahymena can be grown in a large quantity in the laboratory with ease, it has been a great source for biochemical analysis for years, specifically for enzymatic activities and purification of sub-cellular components.

[5][6] Studies on Tetrahymena have contributed to several scientific milestones including: The life cycle of T. thermophila consists of an alternation between asexual and sexual stages.

Typical of ciliates, T. thermophila differentiates its genome into two functionally distinct types of nuclei, each specifically used during the two different stages of the life cycle.

After a brief period of co-stimulation (~1hr), starved cells begin to pair at their anterior ends to form a specialized region of membrane called the conjugation junction.

It is at this junctional zone that several hundred fusion pores form, allowing for the mutual exchange of protein, RNA and eventually a meiotic product of their micronucleus.

However, the macronucleus is only propagated from one cell to the next during the asexual, vegetative stage of the life cycle, and so it is never directly inherited by sexual progeny.

[15] Treatment with the DNA alkylating agent methyl methanesulfonate also resulted in substantially elevated Rad 51 protein levels.

The Sgs1 helicase appears to promote the non-crossover outcome of meiotic recombinational repair of DNA,[18] a pathway that generates little genetic variation.

T. vorax is known for its inducible trophic polymorphisms, an ecologically offensive tactic that allows it to change its feeding strategy and diet by altering its morphology.

While T. vorax is the most well studied Tetrahymena that exhibits inducible trophic polymorphisms, many lesser known species are able to undertake transformation as well, including T. paulina and T.

These morphological switches are triggered by an abundance of stomatin in the environment, a mixture of metabolic compounds released by competitor species, such as Paramecium, Colpidium, and other Tetrahymena.

Specifically, chromatographic analysis has revealed that ferrous iron, hypoxanthine, and uracil are the chemicals in stomatin responsible for triggering the morphological change.

When the chemical inducers are in high concentration, T. vorax cells will transform at higher rates, allowing them to prey on their former trophic competitors.

mRNA and amino acid sequencing indicate that ubiquitin may play a crucial role in allowing transformation to take place as well.

In T. thermophila, chromosome amplification and gene expansion are inducible responses to common organometallic pollutants such as cadmium, copper, and lead.

When researchers grew a sample of the T. thermophila population in normal growth medium (lacking Cd2+) for one month, the number of MTT1, MTT3, and CNBDP genes decreased to an average of three copies (135C).

Thus, the authors argue that chromosome amplification is an inducible and reversible mechanism in the Tetrahymena genetic response to metal stress.

Rather, researchers believe that the duplication resulted from homologous recombination events, producing transcriptionally active, upregulated genes that carry repeated MTT1.

[27] Some strains of T. thermophila have also been found to develop a single, non-beating, enlarged cilia that assists the cell in steering or directing movement.

While the behavior has been shown to correlate with faster dispersal and form as a reversible trait in Tetrahymena cells, little is known about the genetic or cellular mechanisms that allow for its development.