These cells appear to be the ring neurons that project to the ellipsoid body. The antibody also decorates neuropil and cell bodies in the antennal lobes, albeit with lower intensity. Null leonardo mutants die as mature embryos. In the absence of Tor, overexpression of leo is sufficient to activate tll expression. The effect of leo requires D-Raf and Ras1 activities but not KSR or DOS, two recently identified essential components of Drosophila RTK signaling pathways.
Tor signaling is impaired in embryos derived from females lacking maternal expression of leo .
Studies of Drosophila and other insects have indicated an essential role for the mushroom bodies in learning and memory. The gene is expressed abundantly and preferentially in mushroom body neurons. Mutant alleles that reduce Leonardo protein levels in the mushroom bodies significantly decrease the capacity for olfactory learning, but do not affect sensory modalities or brain neuroanatomy that are requisite for conditioning. Clones of mutant leonardo show a loss of photoreceptors. Ommatidia lack outer as well as inner photoreceptors.