Is Grease the Word? Part II: Morphogens

Science's STKE  10 May 2005:
Vol. 2005, Issue 283, pp. tw176
DOI: 10.1126/stke.2832005tw176

During development, secreted signaling molecules called morphogens form concentration gradients to mediate both short-range (a few cell diameters) and long-range (many cell diameters) signals. How morphogens such as those in the Wingless and Hedgehog families--which are covalently linked to lipids that promote their association with the cell membrane--move long distances through the hydrophilic extracellular milieu has been unclear (see Mann and Culi). Panáková et al. used biochemical fractionation together with Western analysis and immunoprecipitation to show that a portion of the larval Drosophila Wingless and Hedgehog protein was associated with low-density lipoprotein particles (lipophorins) rather than with the cell membrane. Immunofluorescence analysis of imaginal discs (which give rise to adult structures such as wings) revealed that Wingless and Hedgehog colocalized in endosomes with fluorescently labeled lipophorin. Hedgehog accumulated near the sites at which it was produced, and the distance over which both Hedgehog and Wingless signaled was attenuated in flies in which lipophorin production was reduced through RNAi directed against apolipophorins I and II. Thus, the authors propose that hydrophobic morphogens such as Hedgehog and Wingless move through tissues in association with lipoprotein particles.

D. Panáková, H. Sprong, E. Marois, C. Thiele, S. Eaton, Lipoprotein particles are required for Hedgehog and Wingless signalling. Nature 435, 58-65 (2005). [PubMed]

R. S. Mann, J. Culi, Morphogens hitch a greasy ride. Nature 435, 30-33 (2005). [PubMed]