Most of us have a junk drawer full of an assortment of items that can be really useful in the right circumstances. The trick is being able to find those items in the seemingly random mess when you need them. That’s the problem faced by the eukaryotic cell. Human cells have roughly 6 feet of DNA full of useful genes jammed into a nucleus that is roughly 10 micrometers (0.00001 meters) in diameter. The cell has to sort through the mess to express the genes that it needs. This searching process is facilitated by the regulated packaging of the DNA by chromosomal proteins into chromatin. The differential packaging that makes specific regions of the DNA more or less accessible in different cells at different times is referred to as epigenetic regulation and is the subject of active research.

The problem of DNA packaging and organization gets even more difficult in sperm cells. The nucleus in human sperm are only about 3 micrometers in diameter, about a third the size of a regular cell nucleus. That level of compaction involves a set of sperm-specific chromosomal proteins. SU Biology faculty member Glenn Yasuda has been studying the sperm proteins that package the ends of the chromosomes called telomeres in the fruitfly model system with collaborators at the University of Washington. The telomere cap protects the ends of the chromosomes and positions them in the highly condensed sperm nucleus. Fertilization by sperm containing uncapped telomeres from mutant fly males results in the fusion and shredding of chromosomes and embryonic lethality. These observations are similar to those made in human cells where defects in the telomere capping complex is associated with chromosome fusion events, genomic instability, and cancer.