Morphogenesis of the Drosophila antennal auditory structure in the pupa, with a focus on the connection between the sensory organ and the exoskeleton

Hearing is an important physiological function for animals to perceive their external environment and to communicate with each other. For example, Drosophila females use their antennae to recognize species-specific courtship songs produced by males. In Drosophila , sounds are detected by the Johnston’s Organs (JO), an array of mechanoreceptors located in the second antennal segment (a2). Sounds cause vibration of the distal (third) antennal segment (a3), which in turn causes rotation of the a2-a3 joint exoskeleton, to which the JO is connected. The a2-a3 joint exhibits an elaborate structure, and mutations that disrupt the structure are associated with hearing defects. How the elaborate joint structure and its connection to the JO develop remains to be understood. Here we show their morphogenetic processes during the pupal stage, with focus on the a2-a3 joint and JO. We first describe invagination of the epidermis at the a2-a3 joint prior to cuticle formation. Then we clarify how the cellular and extracellular structures of the JO that mediate its attachment to the a2-a3 joint exoskeleton (epidermis/cuticle) develop. We further searched for genes that were expressed in the a2-a3 joint epidermis, as a step toward exploring the genetic pathway regulating the JO-exoskeleton connection. We found that an enhancer trap of big brain ( bib ), a target gene of Notch signaling, was expressed in the a2-a3 joint epidermis.