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Eukaryotic Cell, December 2006, p. 2114-2119, Vol. 5, No. 12
1535-9778/06/$08.00+0     doi:10.1128/EC.00059-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Consequences of Telomere Shortening at an Active VSG Expression Site in Telomerase-Deficient Trypanosoma brucei{triangledown} ,{dagger}

Oliver Dreesen and George A. M. Cross*

Laboratory of Molecular Parasitology, The Rockefeller University, New York, New York

Received 24 February 2006/ Accepted 16 October 2006

Trypanosoma brucei evades the host immune response by sequential expression of a large family of variant surface glycoproteins (VSG) from one of ~20 subtelomeric expression sites (ES). VSG transcription is monoallelic, and little is known about the regulation of antigenic switching. To explore whether telomere length could affect antigenic switching, we created a telomerase-deficient cell line, in which telomeres shortened at a rate of 3 to 6 bp at each cell division. Upon reaching a critical length, short silent ES telomeres were stabilized by a telomerase-independent mechanism. The active ES telomere progressively shortened and frequently broke. Upon reaching a critical length, the short active ES telomere stabilized, but the transcribed VSG was gradually lost from the population and replaced by a new VSG through duplicative gene conversion. We propose a model in which subtelomeric-break-induced replication-mediated repair at a short ES telomere leads to duplicative gene conversion and expression of a new VSG.

* Corresponding author. Mailing address: Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6307. Phone: (212) 327-7571. Fax: (212) 327-7845. E-mail: george.cross{at}rockefeller.edu.

{triangledown} Published ahead of print on 27 October 2006.

{dagger} Supplemental material for this article may be found at http://ec.asm.org/.

Eukaryotic Cell, December 2006, p. 2114-2119, Vol. 5, No. 12
1535-9778/06/$08.00+0     doi:10.1128/EC.00059-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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