The Drosophila short gastrulation gene (sog) encodes Sog, an extracellular antagonist that blocks signals elicited by Dpp, a member of the bone morphogenetic protein (BMP) superfamily. The expression of a Sog gradient in the dorsal region is thought to result in the concomitant reciprocal gradient of Dpp. Yu et al. studied the effects of Sog on wing development in adult flies and found that Sog only abrogates signaling by the Glass-bottom-boat (Gbb) protein and not signaling by Dpp. Truncated forms of Sog, called Supersog, were observed in embryonic and pupal cells but not larval cells, revealing that Sog is processed in vivo in a developmentally regulated manner. Expression of Supersog in Drosophila led to inhibition of both Dpp signaling and Gbb signaling, indicating that Supersog was able to inhibit a broader range of signaling pathways in the developing fly wing. The metalloproteinase Tolloid (Tld) degrades Sog to an inactive form. However, Yu et al. present evidence that Sog is proteolytically processed into Supersog by Tld, in a complex with the Twisted Gastrulation (Tsg) protein. Thus, whereas Tld alone degrades Sog, the subsequent expression of Tsg may modify Tld proteolytic activity, leading to the formation of active Supersog. This may establish the gradient required to regulate Dpp activity and subsequent differentiation of the dorsal region.
Yu, K., Srinivasan, S., Shimmi, O., Biehs, B., Rashka, K.E., Kimelman, D., O'Connor, M.B., and Bier, E. (2000) Processing of the Drosophila Sog protein creates a novel BMP inhibitory activity. Development 127: 2143-2154. [Online Journal]