Microsurgically-extracted metaphase chromosomes of the Indian muntjac examined with phase contrast and scanning electron microscopy

Abstract

Metaphase chromosomes are extracted from Indian muntjac cultured fibroblasts either through the use of microneedles or by the application of a droplet of silicone oil onto the cell surface. Interconnecting fibers among the chromosomes allow the entire diploid complement to be extracted from the cell. The seven muntjac chromosomes are brought to the surface of a glass coverslip for analysis. Each chromosome can be identified on the basis of morphology, and particular chromosomes or chromosome parts can be isolated. Many of the fibers which interconnect the chromosomes may be attributed to adhesions formed between the sticky chromosome surfaces during extraction. However, when interchromosomal contacts are avoided during extraction, the chromosomes are found to be arranged radially with the centromeres near the center and interconnected by fibers. This arrangement is similar to that seen inside muntjac cells at metaphase. Scanning electron microscopy reveals the chromosome surfaces to consist of looping fibers, except for regions near the centromeres and the secondary constrictions. Chromosome fibers at these sites are organized into parallel bundles. Chromosome interconnections are strands composed of multiple fibers which seem to be continuous with chromosome fibers.