Identification of centromeric antigens in dicentric Robertsonian translocations: CENP-C and CENP-E are necessary components of functional centromeres.

Robertsonian translocations are the most common structural dicentric rearrangements in humans. The stability of these dicentrics is attributed to the inactivation of one centromere by mechanisms which are currently unknown. The presence and amounts of centromeric proteins (CENPs) differ between the centromeres of the few dicentrics which have been studied, providing a limited understanding of the protein components necessary for centromeric function. However, CENP-C previously has been observed only at the active centromeres in two dicentric chromosomes. In the present investigation, the presence and localizations of several centromeric antigens, CENP-B, -C and -E, have been determined in 12 dicentric Robertsonian translocations. Each translocation was studied initially using in situ hybridization with alpha-satellite DNA probes to determine the active centromere. Subsequent immunofluorescence of monoclonal and polyclonal antibodies generated to various centromeric antigens demonstrated that the protein composition differs at the two centromeres of these dicentric translocations. While CENP-B was present at both active and inactive centromeres, CENP-C and -E were located at active centromeres only in the majority of translocations. These results confirm previous observations of CENP-C at active centromeres and provide the first evidence that CENP-E correlates with active centromeres as well, demonstrating that at least two specific centromeric proteins are required for human centromeric function.