The centromere is the plate on which a kinetochore is served. That plate, however, is mysterious. Recently, a group of cell biologists dug into this mystery by forming kinetochores on chromosome regions not typically associated with kinetochores.
Kinetochores are multi-protein structures that serve as the sites of spindle attachment for each chromosome during mitosis. Kinetochores are assembled on regions of the chromosomes known as the centromere. Although the importance of the centromere has long been appreciated, the exact qualities of centromere-ness remain unresolved. Some past research shows that centromere location in budding yeast is based on DNA sequence, while other organisms rely on repeated DNA sequences or epigenetic marks (meaning not due to DNA sequence) to identify the location of a centromere. A recent paper describes a technique that triggers brief over-expression of one of those epigenetic marks—the protein CID (Drosophila CENP-A or CENH3 for those keeping score). After a pulse of this over-expression, chromosomes are coated with CID signal (green, middle image above), yet after a few generations of cell division, those CID marks are mostly cleared away (right image). The remaining CID marks (arrows), Olszak and colleagues found, became sites of new functional kinetochores. By monitoring the early steps of kinetochore formation, these biologists hope to understand how centromere position is determined.
Agata M. Olszak, Dominic van Essen, António J. Pereira, Sarah Diehl, Thomas Manke, Helder Maiato, Simona Saccani & Patrick Heun (2011). Nature Cell Biology 13,799–808. DOI: 10.1038/ncb2272.
Adapted by permission from Macmillan Publishers Ltd, copyright 2011