huckebein specifies aspects of CNS precursor identity required for motoneuron axon pathfinding.

huckebein encodes a putative zinc finger protein expressed in a subset of Drosophila CNS precursors, including the NB 4-2/GMC 4-2a/RP2 cell lineage. In huckebein mutant embryos, GMC 4-2a does not express the cell fate marker EVEN-SKIPPED; conversely, huckebein overexpression produces a duplicate EVEN-SKIPPED-positive GMC 4-2a. We use Dil to trace the entire NB 4-2 lineage in wild-type and huckebein mutant embryos. Loss of huckebein does not affect the number, position, or type of neurons in the NB 4-2 lineage; however, all motoneurons show axon pathfinding defects and never terminate at the correct muscle. Thus, huckebein regulates aspects of GMC and neuronal identity required for proper motoneuron axon pathfinding in the NB 4-2 lineage.