The membrane-localized intracellular protein Numb is known to antagonize Notch signalling in several developmental contexts, such as during mesodermal development in Drosophila. But now, surprisingly, Range and co-workers report that the sea urchin homologue of Numb (LvNumb) regulates Notch signalling positively during the specification of non-skeletal mesoderm (NSM) cells in sea urchin embryos (see p. 2445). The researchers show that LvNumb protein localizes to the presumptive NSM cells in early embryos. By injecting LvNumb RNA and antisense morpholinos, they demonstrate that LvNumb is needed for the specification of all the NSM cell types. The authors also show that LvNumb acts synergistically with Notch during NSM specification and that, unlike in other systems, LvNumb does not need to interact with the endocytic machinery to regulate Notch signalling. Numb might, the researchers speculate, regulate Notch positively by binding to other unknown factors, the identification of which could provide new insights into Notch and Numb signalling and shed light on the changing role of Numb during evolution.
- © 2008.