CTC1-mediated C-strand fill-in is an essential step in telomere length maintenance.
To prevent progressive telomere shortening as a result of conventional DNA replication, new telomeric DNA must be added onto the chromosome end. The de novo DNA synthesis involves elongation of the G-rich strand of the telomere by telomerase. In human cells, the CST complex (CTC1-STN1-TEN1) also functions in telomere replication. CST first aids in duplication of the telomeric dsDNA. Then after telomerase has extended the G-rich strand, CST facilitates fill-in synthesis of the complementary C-strand. Here, we analyze telomere structure after disruption of human CTC1 and demonstrate that functional CST is essential for telomere length maintenance due to its role in mediating C-strand fill-in. Removal of CTC1 results in elongation of the 3΄ overhang on the G-rich strand. This leads to accumulation of RPA and telomeric DNA damage signaling. G-overhang length increases with time after CTC1 disruption and at early times net G-strand growth is apparent, indicating telomerase-mediated G-strand extension. In contrast, C-strand length decreases continuously, indicating a deficiency in C-strand fill-in synthesis. The lack of C-strand maintenance leads to gradual shortening of the telomeric dsDNA, similar to that observed in cells lacking telomerase. Thus, telomerase-mediated G-strand extension and CST-mediated C-strand fill-in are equally important for telomere length maintenance.
Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA.
Xuyang
X
Feng
Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA.
Shih-Jui
SJ
Hsu
Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA.
Christopher
C
Kasbek
Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA.
Mary
M
Chaiken
Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45230, USA.
Carolyn M
CM
Price
D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004256:DNA Polymerase I / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D017353:Gene Deletion; D005786:Gene Expression Regulation; D045325:HCT116 Cells; D057809:HEK293 Cells; D006801:Humans; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D016615:Telomere / Q000378:metabolism* / Q000648:ultrastructure; D059505:Telomere Homeostasis; D059506:Telomere Shortening; D034501:Telomere-Binding Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism
C544945:Ctc1 protein, human; C544946:Stn1 protein, human; D034501:Telomere-Binding Proteins; C544947:Ten1 protein, human; D004247:DNA; C509186:TERT protein, human; D019098:Telomerase; D004256:DNA Polymerase I