The Ciliates
Math 297/Biol 497
Biomolecular Computing in
Nature
The
Ciliates
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The ciliates are characterized by being single-cell organisms containing two types of nuclei in the same cytoplasm, and containing cilia. Despite these unifying features, the ciliates present a very diverse range of genetic organization. A taxonomy of ciliates can be found at the NCBI Taxonomy Homepage. Click on "Eukaryota", then click on "Alveolata", then "Ciliophora".
The two types of nuclei present in ciliates are named micronuclei and macronuclei. Their micronuclear genome is organized very differently from their macronuclear genome. In a precise sense the micronuclear genome is an encrypted version of the macronuclear genome.
Ciliates proliferate by cell division, and service their genomes by means of conjugation. During conjugation a mating pair swap haploid copies of their micronuclei. Subsequently the donated haploid copy, and a resident haploid copy are fused to form a new diploid micronucleus containing genetic material from each of the two conjugants. This new micronucleus is the source from which new micro- and macro-nuclei are formed to replace all prior micro- and macro-nuclei. There are two more scenarios that initiate decryption of a micronucleus: autogamy in some species of ciliates, and in the karyorelictid ciliates, cell division initiates micronuclear decryption.
Following conjugation new macronuclei are constructed from new micronuclei by decryption of micronuclei. This process is the topic of this course. It should be understood that though there is a lot of data available regarding this ciliate cryptosystem, this data is for only very few ciliate species, and as will become clear during the course, this data is still very limited. Also the significance of maintaining an encrypted version of the genome is unknown. At first glance this strategy of genome maintenance appears "expensive": Yet, the ciliates is an ancient and very successful group.