Sexual dimorphism is a widely acknowledged biological phenomenon, yet the mechanisms underlying specific developmental dimorphisms are largely unknown. As a result of the defined connectome available for both C. elegans males and hermaphrodites, it is clear that there are dimorphic wiring differences in shared neurons between the adult animals of the two sexes (1). Several of these dimorphisms are found in the phasmid sensory neurons, whose synapses onto the command interneurons are sexually dimorphic, suggesting that they have sex-specific functions. I am confirming the predicted sex-specific functions of the phasmid neurons using behavioral assays. To study how these dimorphic patterns of connectivity (and function) are established, I am using transsynaptic labeling (GRASP technology; 2) to visualize both male-specific and hermaphrodite-specific synaptic connections of phasmid neurons. Sexual determination is regulated across many invertebrate and vertebrate species by the highly-conserved doublesex/mab (DM) domain genes. In C. elegans, the DM domain class contains 11 paralogs, the majority of which have no known function. I analyzed expression patterns for 8 of the dmd genes in both larval and adult stages in the two sexes to identify dimorphisms, and identified
dmd-4 as a candidate for dimorphic regulation in the PHA and PHB phasmid neurons.
dmd-4 is an embryonic lethal gene, so I am generating a conditional knockout allele and perform mosaic rescue analysis to determine if
dmd-4 is part of the genetic regulatory system for dimorphism in the phasmid neurons, and if this function is cell-autonomous. Ultimately, we will seek to elucidate the genetic regulatory logic of dimorphisms in shared neurons.1. Jarrell TA, Wang Y, Bloniarz AE, Brittin CA, Xu M, Thomson JN, Albertson DG, Hall DH, Emmons SW. 2012. Science 337, 437-444.2. Feinberg EH, VanHoven MK, Bendesky A, Wang G, Fetter RD, Shen K, Bargmann CI. 2008. Neuron 57(3), 353-363.