Cell Image of the Month - Let there be SUN

Staining of SUN2 (green) in the nuclear membrane with microtubules (red) in A-431 cells.

SUN2 (Sad1 and UNC84 domain containing 2), found in the nuclear membrane of cells, is an essential protein for many cellular processes. SUN plays a large role in the organization of multi-nucleated muscle cells, and dysregulation of SUN can cause muscular dystrophy among other diseases.

It is winter time with short days and long, dark nights. Everyone is in need for some sun, and so are your cells. But in cells, SUN (green) is a protein located at the nuclear membrane. The nuclear membrane is the selective barrier between the nucleus and the cytosol, but also provides physical rigidity to the nucleus, organizes chromatin, and is important in meiotic chromosome pairing (Worman & Gunderson 2006). These functions are fulfilled by interactions with the cytoskeleton, on the cytosolic site with the microtubules and on nuclear site with the lamina network. The interactions are mediated by protein complexes containing SUN proteins. SUN proteins reside in the inner nuclear membrane and bind to the lamina as well as to chromatin, which has been hypothesized to regulate gene expression (Van de Vosse et al. 2012).

The loss of SUN proteins has been linked to the development of cancer and diseases (Haque et al. 2010). One example is muscle dystrophy that is denoted by a weakening of skeletal muscles. Muscle cells contain multiple nuclei, and the correct positioning of the nuclei are essential for the correct function of the muscle. SUN proteins play a role in this positioning, and mice models show that mice without SUN proteins die shortly after birth (Lei et al. 2009).