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.

Human TEN1 maintains telomere integrity and functions in genome-wide replication restart.

TEN1 is a component of the mammalian CTC1-STN1-TEN1 complex. CTC1 and/or STN1 functions in telomere duplex replication, C-strand fill-in, and genome-wide restart of replication following fork stalling. Here we examine the role of human TEN1 and ask whether it also functions as a specialized replication factor.

Human CST has independent functions during telomere duplex replication and C-strand fill-in.

Human CST (CTC1-STN1-TEN1) is an RPA-like complex that is needed for efficient replication through the telomere duplex and genome-wide replication restart after fork stalling. Here, we show that STN1/CST has a second function in telomere replication during G-overhang maturation. Analysis of overhang structure after STN1 depletion revealed normal kinetics for telomerase-mediated extension in S phase but a delay in subsequent overhang shortening.

Human CST promotes telomere duplex replication and general replication restart after fork stalling.

Mammalian CST (CTC1-STN1-TEN1) associates with telomeres and depletion of CTC1 or STN1 causes telomere defects. However, the function of mammalian CST remains poorly understood. We show here that depletion of CST subunits leads to both telomeric and non-telomeric phenotypes associated with DNA replication defects.

Mps1 phosphorylation sites regulate the function of centrin 2 in centriole assembly.

The nondegradable Mps1(Δ12/13) protein drives centriole overproduction, suggesting that Mps1 phosphorylates a subset of centrosomal proteins to drive the assembly of new centrioles. Here we identify three Mps1 phosphorylation sites within the centriolar protein Centrin 2 (Cetn2). Although centrioles can be assembled in the absence of Cetn2, centriole assembly is attenuated in the absence of Cetn2.

Antizyme restrains centrosome amplification by regulating the accumulation of Mps1 at centrosomes.

Extra centrosomes are found in many tumors, and their appearance is an early event that can generate aberrant mitotic spindles and aneuploidy. Because the failure to appropriately degrade the Mps1 protein kinase correlates with centrosome overproduction in tumor-derived cells, defects in the factors that promote Mps1 degradation may contribute to extra centrosomes in tumors. However, while we have recently characterized an Mps1 degradation signal, the factors that regulate Mps1 centrosomal Mps1 are unknown.

Mps1 as a link between centrosomes and genomic instability.

Centrosomes are microtubule-organizing centers that must be precisely duplicated before mitosis. Centrosomes regulate mitotic spindle assembly, and the presence of excess centrosomes leads to the production of aberrant mitotic spindles which generate chromosome segregation errors. Many human tumors possess excess centrosomes that lead to the production of abnormal spindles in situ.

Preventing the degradation of mps1 at centrosomes is sufficient to cause centrosome reduplication in human cells.

Supernumerary centrosomes promote the assembly of abnormal mitotic spindles in many human tumors. In human cells, overexpression of the cyclin-dependent kinase (Cdk)2 partner cyclin A during a prolonged S phase produces extra centrosomes, called centrosome reduplication. Cdk2 activity protects the Mps1 protein kinase from proteasome-mediated degradation, and we demonstrate here that Mps1 mediates cyclin A-dependent centrosome reduplication.