During the development of the nervous system, neurons extend axons along defined routes to their targets to form proper connections. We are investigating the roles of a novel protein PQN-55 in axon targeting and synaptogenesis.
pqn-55 belongs to a novel conserved protein family including Drosophila Curta and mouse Q5U4B9. These proteins share an N-terminal Zn-binding SWIM (for SWI2/SNF2 and MuDR) domain followed by several conserved regions. SWIM domain is generally thought to bind DNA and proteins, and has recently been shown to function in ubiquitination(1). The Drosophila Curta gene functions in retinal axon targeting. To explore the functions of this family of proteins, we have begun an analysis of the C. elegans
pqn-55. PQN-55 is broadly expressed in many tissues including neurons and muscles and shows cytoplasmic localization. By transgene analysis of
pqn-55 deletion constructs, we identified that a conserved region in the middle of the protein appeared to be sufficient for the cytoplasmic localization. We isolated one deletion mutation that likely eliminates the function of
pqn-55. The homozygous
pqn-55 mutant animals are viable and display defects in egg-laying and movement. By rescuing experiments, we show
pqn-55 functions cell-autonomously in neurons for Egl and Unc. The overall axon morphology for motor neurons and touch neurons is normal. Immunostaining for synaptotagmin, RIM, ELKS and SYD-2/Liprin shows a grossly normal localization at the synapses. The synaptic patterns for several types of neurons, including HSN are also largely normal. These preliminary data suggest that
pqn-55 may not have a major role in trafficking synaptic components or synaptogenesis. We are further exploring the genetic interactions of
pqn-55 with known axon guidance and synapse molecules. Reference: 1. Nishito, Y. et al. Biochem. J. (2006) 396, 411.