A fosmid reporter construct, which contains more than 30 kb surrounding the
ttx-3 locus and which rescues the AIY differentiation defect of
ttx-3 mutant animals, mirrors the expression of a smaller, locus-restricted reporter construct described earlier (Altun-Gultekin et al., 2001) in the AIY, the AIA, the AIN and a previously uncharacterized neuronal pair in the pharyngeal nervous system. Based on position, morphology and colabeling with the NSM marker
mgl-1::mCherry, the authors identified the pharyngeal neurons that express
ttx-3 as the NSM neuron pair. There are also notable differences in the expression pattern of the fosmid reporter and the smaller reporters. First, expression in the AIN neurons is maintained throughout development with the fosmid reporter, whereas it is restricted to embryos with smaller reporters (Bertrand and Hobert, 2009). Second, the expression in amphid sensory neurons is markedly different. In larval and adult animals, the fosmid reporter is expressed in the ASK neuron class, whereas the smaller reporters are expressed in the ADL and ASI sensory neurons.