A SOLO performance in meiotic cohesion

EGF takes dual control of mRNA E GF coordinates the nuclear and cy t o p l a s m i c activities of an RNA-binding protein to ensure a specifi c mRNA is translated at the right time and place in neu-rons, say Tsai et al. mRNAs localize to specifi c regions within neurons, where they can be translated to quickly generate large amounts of a protein in the place where it is needed. Due to the large size of neurons, this is much more effi cient than translating all mRNAs in a single place and then shipping out each protein to its site of action. But the movement and translation of these mRNAs must be tightly regulated, potentially by extracellular signals such as growth factors. Tsai et al. discovered that EGF boosts expression of the ␬-opioid receptor (KOR) by stimulating both the nuclear export and translation of KOR mRNA. The key to this dual control was an RNA-binding protein called Grb7. EGF prods a phosphatase called SHP-2 to dephosphorylate Grb7 in the nucleus, prompting it to bind KOR mRNA and recruit a protein complex involved in nuclear export. But EGF also stimulated focal adhesion kinase to rephosphorylate Grb7 in the cytoplasm, causing it to release the mRNA for translation into KOR protein. Senior author Li-Na Wei is now investigating what happens in between nuclear exit and translation. mRNA is transported from the cell body to the axons, a process that is also likely to be regulated, perhaps by signals other than EGF. The researchers are also interested to discover the signals that regulate the localization and translation of other mRNAs. Y an et al. describe how a D ro s o p h i l a protein works with the cohesin complex to hold sister chromatids together during meiosis, ensuring their faithful segregation into sperm. Just as in mitosis, the cohesin complex keeps sister chromatids together until they separate in the second of meiosis' two divisions. In addition, sister chromatid cohesion helps homologous chromosomes pair up and divide in the fi rst meiotic division. But the function of cohesins in Drosophila meiosis is largely unknown because mutations in the proteins are lethal, and fl ies lack a homologue of the meiosis-specifi c cohesin Rec8. Yan et al. investigated a previously uncharacterized protein called SOLO (sisters on the loose), and found that it colocalized with the cohesin subunit SMC1 …