Systematic expression profiling of dprs and DIPs reveals cell surface codes in Drosophila larval peripheral neurons

In complex nervous systems, neurons must identify their correct partners to form synaptic connections. The prevailing model to ensure correct recognition posits that cell surface proteins (CSPs) in individual neurons act as identification tags. Thus, knowing what cells express which CSPs would provide insights into neural development, synaptic connectivity, and nervous system evolution. Here, we investigated expression of dprs and DIPs, two CSP subfamilies belonging to the immunoglobulin superfamily (IgSF), in Drosophila larval motor neurons (MNs), sensory neurons (SNs), peripheral glia and muscles using a collection of GAL4 driver lines. We found that dprs are more broadly expressed than DIPs in MNs and SNs, and each examined neuron expresses a unique combination of dprs and DIPs. Interestingly, many dprs and DIPs are not robustly expressed, but instead, are found in gradient and temporal expression patterns. Hierarchical clustering showed a similar expression pattern of dprs and DIPs in neurons from the same type and with shared synaptic partners, suggesting these CSPs may facilitate synaptic wiring. In addition, the unique expression patterns of dprs and DIPs revealed three uncharacterized MNs - MN23-Ib, MN6-Ib (A2) and MN7-Ib (A2). This study sets the stage for exploring the functions of dprs and DIPs in Drosophila MNs and SNs and provides genetic access to subsets of neurons.