Uncoupling Sonic hedgehog control of pattern and expansion of the developing limb bud.
Sonic hedgehog (Shh), which regulates proliferation in many contexts, functions as a limb morphogen to specify a distinct pattern of digits. How Shh's effects on cell number relate to its role in specifying digit identity is unclear. Deleting the mouse Shh gene at different times using a conditional Cre line, we find that Shh functions to control limb development in two phases: a very transient, early patterning phase regulating digit identity, and an extended growth-promoting phase during which the digit precursor mesenchyme expands and becomes recruited into condensing digit primordia. Our analysis reveals an unexpected alternating anterior-posterior sequence of normal mammalian digit formation. The progressive loss of digits upon successively earlier Shh removal mirrors this alternating sequence and highlights Shh's role in cell expansion to produce the normal digit complement.
SciCrunch is a data sharing and display platform. Anyone can create a custom portal where they can select searchable subsets of hundreds of data sources, brand their web pages and create their community. SciCrunch will push data updates automatically to all portals on a weekly basis. User communities can also add their own data to scicrunch, however this is not currently a free service.