CENP-E is a kinesin-7 family motor protein that localizes specifically to kinetochores during mitosis and plays essential roles in establishing stable kinetochore-microtubule attachments and ensuring accurate chromosome segregation. The protein is recruited to centromeres, the specialized chromosomal regions that form the foundation for kinetochore assembly, where it functions as a plus-end-directed motor that moves along spindle microtubules. Unlike constitutive centromere proteins, CENP-E expression and localization are tightly restricted to the mitotic phase of the cell cycle, making it a distinctive mitosis-specific component of the chromosome segregation machinery.
The mechanistic function of CENP-E involves using ATP hydrolysis to generate directional movement along microtubules, which enables it to capture lateral kinetochore-microtubule attachments and convert them into stable end-on attachments at the kinetochore outer plate. This motor activity is particularly important for congressing polar chromosomes to the metaphase plate and for correcting erroneous attachments such as merotely, where a single kinetochore is attached to microtubules from both spindle poles. In vitro studies have demonstrated that CENP-E can transport cargo along microtubules and bind to both microtubules and kinetochore components simultaneously, suggesting it acts as a molecular tether.
Despite this established framework, several aspects of CENP-E function remain contested or poorly understood. The relationship between CENP-E reduction and aneuploidy appears complex, with in vitro experiments showing that partial CENP-E depletion can generate chromosome missegregation, but the precise threshold levels required for faithful segregation and whether merotely is the primary error mode remain unclear. Additionally, whether CENP-E motor activity is absolutely required for all its functions or whether it can act as a passive structural scaffold in some contexts continues to be investigated.
Member Concepts
Tensions
- Motor protein activity vs Structural scaffold function: CENP-E is defined as a motor protein that generates force through ATP hydrolysis, yet some studies suggest it may also function as a passive structural element linking kinetochores to microtubules. Resolving this tension requires determining whether motor activity is essential for all CENP-E functions or whether ATP-independent scaffolding contributes significantly to chromosome alignment and segregation fidelity.
- In vitro functional requirements vs In vivo chromosome segregation: In vitro experiments demonstrate that CENP-E can function with purified components in controlled environments, but these simplified systems may not capture the full complexity of centromere-kinetochore organization during actual mitosis in living cells. This creates uncertainty about which mechanistic insights from in vitro studies are directly applicable to chromosome segregation in vivo and which require additional cellular context.
- Merotely correction vs Aneuploidy generation: CENP-E is proposed to correct merotelic attachments where one kinetochore binds microtubules from both poles, yet CENP-E reduction generates aneuploidy, implying failure of proper chromosome segregation. The tension lies in whether merotely is the primary mechanism by which CENP-E deficiency causes aneuploidy or whether other attachment errors predominate, which would require distinguishing between different error correction pathways.
Open Questions
- What is the minimal threshold level of CENP-E required to maintain chromosome segregation fidelity in different cell types?
- Does CENP-E motor activity contribute equally to all phases of chromosome congression or are there distinct ATP-dependent and ATP-independent functions?
- How does CENP-E coordinate with other kinetochore components to distinguish correct from incorrect microtubule attachments?
- What determines the mitosis-specific expression and localization pattern of CENP-E compared to constitutive centromere proteins?
- Is merotely the predominant attachment error when CENP-E function is compromised or do other error modes contribute significantly to aneuploidy?