A working model for the evaluation of the motor phenotypes resulting from perturbation of individual members of the <i>Drosophila</i> SMN-Gemins complex.

<p>(A) The interaction map of the <i>Drosophila</i> SMN-Gemins complex is unclear and, here, it is modelled on that drafted for the human version (reviewed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083878#pone.0083878-Cauchi1" target="_blank">[21]</a>). In this regard, SMN associates to Gemin2 and Gemin3. Gemin2, in turn, interacts with Gemin5. All components of the SMN complex are individually required for viability and, importantly, motor behaviour. In particular, they are key for normal flight performance, which is a highly demanding motor activity that relies on correct function of the motor unit. The process or pathway linking the SMN complex to motor behaviour is as yet unclear (indicated by ‘?’) though we speculate that it is predominantly nuclear and, hence, might revolve around snRNP biogenesis and/or recycling. (B) The dead helicase Gem3^ΔN mutant lacks its helicase core but retains the SMN-binding domain. We hypothesise that it hijacks SMN and its associates from the endogenous wild-type Gemin3, hence, forming a non-functional or inactive SMN complex. Gem3^ΔN overexpression mimics the flightless phenotype associated with the loss of Gemin3 function though the phenotype is stronger. (C–E) Reduced Gemin3, Gemin5 or Gemin2 levels through RNAi-mediated knockdown also results in a flightless phenotype. These observations demonstrate that either of these factors performs a critical role that cannot be compensated by the presence of the remaining components. (D) Similar to its Gemin associates, SMN is required in adequate levels for normal flight behaviour as reported in the hypomorphic <i>Smn^E33</i> fly mutant <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083878#pone.0083878-Rajendra1" target="_blank">[43]</a>.