TY - JOUR
T1 - Analysis of Trypanosoma brucei vsg expression site switching in vitro
AU - Horn, David
AU - Cross, George A.M.
N1 - Funding Information:
This work was supported by the National Institutes of Health (grant AI 21729). We thank Kelvin Davies (Rockefeller University) for providing a vsgbR2 cDNA clone, Miguel Navarro (Rockefeller University) for providing a vsgB cDNA clone and Elizabeth Wirtz for critical reading of the manuscript.
PY - 1997/2
Y1 - 1997/2
N2 - Trypanosoma brucei can undergo antigenic variation by switching between distinct telomeric variant surface glycoprotein gene (vsg) expression sites (ESs) or by replacing the active vsg. DNA rearrangements have often been associated with ES switching, but it is unclear if such rearrangements are necessary or whether ES inactivation always accompanies ES activation. To explore these issues, we derived ten independent clones, from the same parent, that had undergone a similar vsg activation event. This was achieved in the absence of an immune response, in vitro, using cells with selectable markers integrated into an ES. Nine of the ten clones had undergone ES switching. Such heritable changes in transcription state occurred at a frequency of approximately 6 x 10-7. Comparison of switched and un-switched clones highlighted the dynamic nature of T. brucei telomeres, but changes in telomere length were not specifically associated with ES switching. Mapping within and beyond the ESs revealed no detectable DNA rearrangements, indicating that rearrangements are not necessary for ES activation/inactivation. Examination of individual cells indicated that ES activation consistently accompanied inactivation of the previously active ES. In some cases, however, we found cells that appeared to have efficiently established the switched state but which subsequently, at a frequency of approximately 2 x 10-3, generated cells expressing both pre- and post-switch vsgs. These results show that ES activation/inactivation is usually a coupled process but that cells can inherit a propensity to uncouple these events.
AB - Trypanosoma brucei can undergo antigenic variation by switching between distinct telomeric variant surface glycoprotein gene (vsg) expression sites (ESs) or by replacing the active vsg. DNA rearrangements have often been associated with ES switching, but it is unclear if such rearrangements are necessary or whether ES inactivation always accompanies ES activation. To explore these issues, we derived ten independent clones, from the same parent, that had undergone a similar vsg activation event. This was achieved in the absence of an immune response, in vitro, using cells with selectable markers integrated into an ES. Nine of the ten clones had undergone ES switching. Such heritable changes in transcription state occurred at a frequency of approximately 6 x 10-7. Comparison of switched and un-switched clones highlighted the dynamic nature of T. brucei telomeres, but changes in telomere length were not specifically associated with ES switching. Mapping within and beyond the ESs revealed no detectable DNA rearrangements, indicating that rearrangements are not necessary for ES activation/inactivation. Examination of individual cells indicated that ES activation consistently accompanied inactivation of the previously active ES. In some cases, however, we found cells that appeared to have efficiently established the switched state but which subsequently, at a frequency of approximately 2 x 10-3, generated cells expressing both pre- and post-switch vsgs. These results show that ES activation/inactivation is usually a coupled process but that cells can inherit a propensity to uncouple these events.
KW - Antigenic variation
KW - Expression site
KW - Telomere
KW - Trypanosama brucei
KW - Variant surface glycoprotein
UR - http://www.scopus.com/inward/record.url?scp=0031043358&partnerID=8YFLogxK
U2 - 10.1016/S0166-6851(96)02794-6
DO - 10.1016/S0166-6851(96)02794-6
M3 - Article
C2 - 9084039
AN - SCOPUS:0031043358
SN - 0166-6851
VL - 84
SP - 189
EP - 201
JO - Molecular and Biochemical Parasitology
JF - Molecular and Biochemical Parasitology
IS - 2
ER -