It may appear that chromosomes are just floating around inside of the nucleus, but that couldn’t be further from the truth. Inside that double membrane of the nucleus is a lot of chromosome choreography, and this is especially true during meiosis. Today’s image is from a paper showing the interaction between two nuclear envelope proteins and their regulation of chromosome dynamics and pairing.
Meiosis is a type of cell division that reduces the number of chromosomes down to one copy of each in the resulting daughter cells, called gametes (eggs and sperm). During meiosis, the pairing of homologous chromosomes (matching chromosomes) is important for recombination and chromosome segregation later in meiosis. Recombination is the exchange of DNA regions between two paired chromosomes, and is key in generating genetic variation. In yeast and worms, KASH domain proteins and SUN domain proteins of the nuclear envelope interact to ensure proper chromosome pairing and positioning within the nucleus. Mammals were known to have a SUN domain protein, SUN1, and a recent paper identified its KASH domain binding partner, KASH5. Morimoto and colleagues found that KASH5 and SUN1 both localize at telomeres, regions at the ends of chromosomes, during meiosis in mice. In addition, KASH5 interacts with the microtubule-associated dynein-dynactin complex to regulate chromosome movement. In the images above, chromosomes from mouse spermatocytes have both KASH5 and SUN1 localized at telomeres throughout meiosis (chromosomes are blue).
Akihiro Morimoto, Hiroki Shibuya, Xiaoqiang Zhu, Jihye Kim, Kei-ichiro Ishiguro, Min Han, & Yoshinori Watanabe (2012). A conserved KASH domain protein associates with telomeres, SUN1, and dynactin during mammalian meiosis originally published in the Journal of Cell Biology, 198 (2), 165-172 DOI: 10.1083/jcb.201204085