Recognition of mammalian centromeres by anti-dynein and anti-dynactin components

Antibodies against one component of dynein, namely IC, and two components of dynactin, namely p50 and p150, were studied for their activity against the centromeres of three mammalian species, human, mouse and Indian muntjac. Ordinarily human and mouse chromosomes carry one dot-like centromere, whereas Indian muntjac has two or three tandemly organized centromeres per chromosome. Dynein and dynactin antigens can be detected on all active centromeres. However, inactive centromeres (which do not bind microtubules and lack a trilamellar kinetochore) in human MDA 435 cells and mouse L cells do not respond to any of the three antibodies. In parallel with their response to CREST serum every Indian muntjac chromosome exhibits more than one anti-dynein or anti-dynactin binding site. The area reacted upon by any of these three antibodies is very precise and apparently associated with the kinetochore at the site of the active centromere. This is in contrast to the label observed with CREST serum, which 'stains' both the active as well as inactive centromeres and spans a considerable distance, including some heterochromatin. The label on colcemid-arrested mouse and human chromosomes was more intense than that observed on untreated chromosomes. In preparations not treated with colcemid metaphase chromosomes in the ring configuration exhibited label with all of the three antibodies. This observation is contrary to the belief that the dynein motor proteins do not persist on centromeres at metaphase.