The centromeres of the Indian muntjac: evidence for the existence of multiple centromeres?

Unlike the centromeres of other species, the "compound' centromeres of the Indian muntjac span over exceptionally extended regions (Brinkley et al., 1984). We extend this concept and show that some of these centromeres are divisible into several chromomeres in which the light staining regions alternate with the dark staining C-band positive segments. Unlike the centromeres of other species where the centromere replicates as one unit, the replication of the sub-units constituting the centromere of the X-chromosome in the muntjac occurs at different times as at least three independent segments. The CREST staining of the centromere regions of even the smallest (Y2) chromosome is interrupted by non-staining segments. Electron microscopy shows similar interruptions in the continuity of the trilamellar kinetochore. Sister chromatid exchanges occur in the region of the centromeres and chromatid breaks within the centromere region occur in the non-fluorescent segments. We interpret these data to suggest that the centromere regions of the Indian muntjac are made up of independent multiple centromeres interrupted by non-centromeric chromatin. Relevance of these parameters in mutagenesis is briefly discussed.