What marks a particular DNA segment for ‘time off’?
DNA tagged for ‘time off’
New york and London aren’t the only cities bursting with activity. The nucleus, an active part of the cell filled with double stranded DNA performs various activities including; opening, closing and transcription.
The nucleus has an effective and flexible ‘border control’ called the lamina meshwork. Proteins travel in and out of the nucleus ‘city’ via the lamina on business binding with different DNA. Increasing evidence suggests this border control not only acts for shape, support and ‘immigration’ purposes, but also for ‘time off’ duty. During time off, certain DNA segments are pulled to the lamina meshwork becoming inaccessible to proteins and turning off segments of the genome.
Time off is particularly critical and delicate in embryogenesis (a cell or embryo developing into a final cell type or organism). During this development, a cell’s fate is determined; one can image a ballot system with stems cells pledging their allegiance to a particular cell type.
Embryogenesis has fascinated scientists for decades. Research has sought to answer many questions including; ‘what marks a particular DNA segment for time off?’ PHD student, Karen Reddy and her team have answered this question by comparing immature, embryonic, skinlike cells to mature immune system cells from mice. They discovered differences occurring near genes that are used differently and consistent DNA regions clinging to the mesh lamina. Upon further investigation, they found the lamina binding DNA segments were able to bind the protein YY1, which then sent the surrounding DNA to the lamina on ‘time off’.
Furthermore, Reddy’s team discovered two molecular tags that are needed for DNA to move to the lamina. Through epigenetic regulation, these tags found on the histone proteins, wrap around the DNA without causing DNA sequence changes. Once a DNA is tagged, it goes to the lamina. Whether YY1 has additional roles, like acting as a magnet to bring the DNA to the lamina.
Whilst DNA gets some time off, this leaves more interesting questions to be answered by Reddy and other scientists.
- J. C. Harr, T. R. Luperchio, X. Wong, E. Cohen, S. J. Wheelan, K. L. Reddy. Directed targeting of chromatin to the nuclear lamina is mediated by chromatin state and A-type lamins. The Journal of Cell Biology, 2015; 208 (1): 33 DOI: 10.1083/jcb.201405110
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