Multiple function of poxn gene in larval PNS development and in adult appendage formation of Drosophila.

The gene pox-neuro (poxn), which encodes a transcriptional regulator including a paired domain, specifies the differences between mono-innervated external sensory (m-es) organs and poly-innervated external sensory (p-es) organs in Drosophila. Here, we analyse the function of poxn in the development of the larval peripheral nervous system (PNS) and in other developmental aspects using a loss-of-function mutant of poxn. We observed that, in addition to the transformation of p-es into m-es organs in the mutant embryo, the external structure of the trichome-like sensilla (hairs) misdifferentiates into that of the campaniform-like sensilla (papillae) in the second and third larval instars. We also observed that POXN is expressed in a cell associated with the external structure of the trichome-like sensilla in the first and second instar larvae. These results imply that poxn is required in two distinct steps in the development of the larval PNS: (1) development of the larval p-es organs during embryogenesis and (2) re-formation of larval sensory hairs after each larval moult. In addition to its expression in the developing PNS, POXN is also expressed in concentric domains of the leg and antennal imaginal discs of early third instar larvae, and in the region of the wing disc that will form the wing hinge. The loss of poxn function results in defects of segmentation of the tarsus and antenna and in a distortion in the wing hinge. These results indicate that the poxn gene plays crucial roles in the morphogenesis of the appendages, in addition to its role in the early specification of neuronal identity.