Thus, we hypothesized that an additional transcription factor could be primarily required for specifying the PVM cell fate. PVM is located on the left

side of the animal and adjacent to the PVD cell soma (Figure 1). Mutants of zag-1(rh315) ( Wacker et al., 2003) showed an extra PVD-like cell in this location ( Figure 5; Table S2) ( Smith et al., 2010). In addition to displaying the highly branched morphology that is characteristic of PVD, the extra PVD-like cell also expressed multiple PVD markers ( Table S1). We considered the possibility that this PVD-like cell could have arisen from duplication of the PVD lineage ( Figure 1). However, the absence of an additional dat-1::mcherry-expressing PDE neuron in zag-1(rh315) excludes this model (data selleck products not shown). Because the C59 wnt PVD sister cell, V5Rpaapp, normally undergoes programmed cell death ( Figure 1), we entertained the alternative idea that this cell survives in the zag-1 mutant

and gives rise to a duplicate PVD neuron. This idea is ruled out, however, by the finding that the introduction of an egl-1 mutation to prevent V5Rpaapp apoptosis ( Conradt and Horvitz, 1998) results in a third PVD-like cell on the left side in the zag-1; egl-1 double mutant (data not shown). Finally, expression of the light touch neuron-specific marker, mec-4::mCherry, was not detected in this region, therefore suggesting that the normal PVM cell is missing in the zag-1 mutant ( Table S1). Based on these results, we conclude that the extra PVD neuron observed in zag-1 mutants arises from the conversion of PVM into a PVD-like

cell. We refer to this converted PVM cell in zag-1 mutants as cPVM. Similar results were obtained for zag-1(ok214) and zag-1(zd86) ( Clark and Chiu, 2003) (data not shown). Megestrol Acetate The timing at which cPVM initiates lateral branching is also consistent with the proposal that PVM is converted to a PVD-like fate in zag-1 mutants. PVM normally arises soon after hatching in the wild-type animal ( Sulston and Horvitz, 1977) ( Figure 1), and cPVM was initially observed in L1 zag-1 mutant animals. Also, as noted earlier for cAVM, the cPVM cell initiated a PVD-like branching pattern in L2 larvae in zag-1 mutants ( Figure 5C), whereas the PVD neuron, which first appears in L2 animals, does not display lateral branches until later, in the L3 stage ( Smith et al., 2010). We used transgenic animals expressing the mosaic PVD::mCherry marker to distinguish PVD versus cPVM lateral branches in later larval stages and in the adult. Random loss of the mCherry marker from PVD but not cPVM confirmed that the PVD-like branching pattern of the cPVM cell is retained during larval development ( Figure 5) (see Experimental Procedures). This analysis also revealed that PVD (marked with PVD::GFP) showed a reduced number of lateral branches in the posterior region occupied by cPVM in the zag-1 mutant ( Figure 5).