Carolyn Jahn
Title: Associate Professor
Research area: Genomic Rearrangements in Ciliates
Degree: Ph.D., Genetics, Cornell University, Graduate School of Medical Sciences
Voice: 312.503.2955
Fax: 312.503.7912
e-mail: c-jahn@northwestern.edu  

Detailed research description:
Genomic rearrangements are known to be associated with human diseases, particularly birth defects and cancer. By studying the controlled genomic rearrangement process that occurs in the hypotrichous ciliated protozoan Euplotes crassus during the formation of a macronucleus, we can determine what DNA sequences and enzymes might be involved and how the process is controlled. Hypotrichous ciliated protozoa dramatically reorganize their DNA in the process of forming a transcriptionally active macronucleus from an inactive micronucleus. The macronucleus contains small linear DNA molecules, each carrying a different gene. The formation of the macronuclear DNA molecules involves recognition of specific fragmentation sites and addition of telomeres, precise elimination of sequences internal to the retained macronuclear sequences, and degradation of the majority of the micronuclear genome.

This process can be studied in Euplotes crassus because large quantities of two different mating types can be grown that, when mixed, undergo synchronous mating, meiosis, and macronuclear development. We have identified two highly abundant (>104 copies per genome), repetitive element families (Tec1 and Tec2) that frequently interrupt the macronuclear-destined sequences. The elements are excised during a discrete period of macronuclear development and can be found as extrachromosomal circles. The abundance of these elements and their excised forms, coupled with the precise timing of excision, provides an ideal starting point for molecular analyses of the mechanisms behind this genomic reorganization process. Our goal is to determine how this process is controlled so that excision occurs in a precise manner at a specific stage of macronuclear development.

Representative publications:

Frels, J.S., Tebeau, C.M., Doktor, S.Z. and Jahn, C.L.
  1996 Differential replication and DNA elimination in the
  polytene chromosomes of Euplotes crassus. Mol. Biol.
  Cell, 7: 755-768.

Jahn, C.L., Ling, Z., Tebeau, C.M. and Klobutcher,
  L.A. 1997 An unusual histone H3 specific for early
  macronuclear development in Euplotes crassus.
  Proc. Natl. Acad. Sci. USA, 94: 1332-1337.

Klobutcher, L.A., Gygax, S., Podoloff, J., Vermeesch, J.,
  Price, C.M., Tebeau, C.M. and Jahn, C.L. 1998 A
  conserved DNA sequence adjacent to chromosome
  fragmentation/telomere addition sites in Euplotes crassus.
  Nucleic Acids Res., 26:4230-4240.

Jahn, C.L. 1999 Differentiation of chromatin during DNA
  elimination in Euplotes crassus. Mol. Biol. Cell, 10: 4217-
  4230.

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