Directing egg traffic: Internal mechanosensory feedback modulates central pattern generation to coordinate ovulation in Drosophila

Successful reproduction requires precise coordination of muscle contractions during ovulation and the motor control has been well investigated in insects. However, the location of the central pattern generator (CPG) and the sensory feedback orchestrating this process remain poorly understood. Using Drosophila , we identify a novel pair of multidendritic mechanosensory neurons (mdn-LO) in the lateral oviducts that express the mechanosensitive channels TMC (transmembrane channel-like protein), PPK (pickpocket), and Piezo. We demonstrate that TMC is essential for ovulation coordination: tmc mutation or neuron-specific knockdown increases egg-jamming at the junction between the lateral and the common oviduct, while ppk or Piezo single mutants reduce egg-laying without causing jamming. Calcium imaging reveals that mdn-LO neurons are rhythmically activated by oviduct contractions, and chemogenetic stimulation of these neurons triggers muscle contractions. Trans-Tango and GRASP (GFP Reconstitution Across Synaptic Partners) analyses show that mdn-LO neurons form synapses with female-specific insulin-like peptide 7 (ILP7)-expressing oviduct motor neurons in the abdominal ganglion. Activating either mdn-LO or ILP7 neurons induces egg-jamming, indicating their roles within a CPG network. Whereas the ILP7 neurons are likely to coordinate oviduct muscle contractions using glutamate, we found that the co-localized ILP7 affects the rate of ovulation, but plays no role in egg jamming. Importantly, the ILP7 neurons exhibit spontaneous rhythmic calcium oscillations, which are regulated by the mechanical feedback generated by egg movement in the oviduct. This novel circuit, including the TMC-expressing mdn-LO neurons and a set of ILP7 neurons, organizes an innate behavior by coupling strategic sensory information and a CPG to ensure bilateral coordination of oviduct contractions to prevent egg jamming during oviposition.