Homeotic proboscipedia cell identity functions respond to cell signaling pathways along the proximo-distal axis.

To better understand how the different cell identities composing a segment are attributed and coordinated under the control of a single homeotic selector gene, we examined dose-sensitive homeotic phenotypes associated with gain-of-function and loss-of-function mutations of the homeotic gene proboscipedia (pb; Hox-A2/-B2). We then employed dose-sensitive segment and cell identity phenotypes resulting from ectopic proboscipedia expression to screen for other interacting loci. We find that pb, as well as the homeotic loci Ultrabithorax, Sex combs reduced and Antennapedia, respond to positional information along the proximo-distal axis. This response for pb implicates at least two signal transduction pathways, those involving Ras1 and Notch.