Early disruption of centromeric chromatin organization in centromere protein A (Cenpa) null mice

Centromere protein A (Cenpa for mouse, CENP-A for other species) is a histo ne H3-like protein that is thought to be involved in the nucleosomal packag ing of centromeric DNA. Using gene targeting, we have disrupted the mouse C enpa gene and demonstrated that the gene is essential. Heterozygous mice ar e healthy and fertile whereas null mutants fail to survive beyond 6.5 days postconception, Affected embryos show severe mitotic problems, including mi cronuclei and macronuclei formation, nuclear bridging and blebbing, and chr omatin fragmentation and hypercondensation, Immunofluorescence analysis of interphase cells at day 5.5 reveals complete Cenpa depletion, diffuse Cenpb foci, absence of discrete Cenpc signal on centromeres, and dispersion of C enpb and Cenpc throughout the nucleus. These results suggest that Cenpa is essential for kinetochore targeting of Cenpc and plays an early role in org anizing centromeric chromatin at interphase, The evidence is consistent wit h the proposal of a critical epigenetic function for CENP-A in marking a ch romosomal region for centromere formation.