September 15, 2011

There is something so gratifying about a light switch. My two-year old will pull a chair to our kitchen light switch to turn it on and off. Over. And over. And over again. Maybe that’s why I find phosphorylation so satisfying (and maybe why I have a headache). It’s a molecular switch, and the vast combinations of where, when, and how different proteins are phosphorylated can provide mind-numbing levels of regulation within a cell. Combine my appreciation for phosphorylation with my absolute love for early worm embryos, and you have today’s lovely images.

The one-cell stage worm embryo divides like many cells throughout development—asymmetrically. Asymmetric cell division results in two daughter cells with different developmental fates and frequently different sizes. For asymmetric cell division to take place in the early worm embryo, the entire mitotic spindle apparatus is moved towards one end of the cell, the posterior. A complex of polarity proteins (made of PAR proteins and the aPKC homolog PKC-3) functions upstream of an evolutionary conserved pathway of proteins (made of the NuMA homolog LIN-5 and G-protein signaling), and a recent paper finds the well sought-after link between these two pathways. In Galli and colleagues’ paper, they show that LIN-5 is phosphorylated by PKC-3. The position of PKC-3 at only one side of the cell results in the phosphorylation of LIN-5 only in that region, which in turns allows the mitotic spindle to position itself correctly. In the images above, one-cell stage worm embryos show staining for phosphorylated LIN-5 (top row, red in bottom row) during mitosis (spindle is in green, chromosomes in blue). Phosphorylated LIN-5 is enriched at higher levels at the anterior cortex (the left-hand side in each image) during earlier stages of mitosis.

Galli, M., Muñoz, J., Portegijs, V., Boxem, M., Grill, S., Heck, A., & van den Heuvel, S. (2011). aPKC phosphorylates NuMA-related LIN-5 to position the mitotic spindle during asymmetric division Nature Cell Biology, 13 (9), 1132-1138 DOI: 10.1038/ncb2315
Adapted by permission from Macmillan Publishers Ltd, copyright ©2011