Worm Breeder's Gazette 11(4): 102
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
The mec-7 gene encodes a -tubulin required for the formation of 15- protofilament microtubules (Genes and Dev. 3:870). These large diameter microtubules are found exclusively in the touch neurons (ALML ALMR, AVM, PVM, PLML, and PLMR) (J. Cell Biol.93:15). mec-7 mutants lack the 15-protofilament microtubules and are touch insensitive. We recently reported that a mec-7-lacZ extrachromosomal element, evEx1, is expressed exclusively in the touch neurons, and at a lesser extent, in the FLP neurons (W.B.G.1140). The gene mec-3 encodes a potential transcription factor that is required for the proper differentiation of the touch neurons (including the appearance of 15- protofilament microtubules) (Cell 54:5). Similarly, mec-3 was previously shown to be expressed in the touch neurons and in the FLPs, but also in the PVD neurons (Genes & Dev. 3:1823). An attractive possibility is that mec-3 directly activates mec-7 expression. However, our mec-7-lacZ construct was found to be expressed at almost normal levels in a mec-3 mutant background, using the presumed null allele u298:Tc1. This led us to propose that the mec-3 gene product was not required to trigger mec-7 transcription (W.B.G. 1140). Here we present recent data which suggest that, in fact, mec-3 is the transcriptional activator of mec-7.First, mec-7 may be transcribed in all the cells that were previously shown to express a mec-3-lacZ fusion gene, i.e. the touch neurons as well as the FLPs and the PVDs. We have stably integrated the mec-7-lacZ fusion gene, following the procedure of Kari et al. (W.B.G. 1114). The integrated evEx1 array has been named jeIn1. Using jeIn1-containing N2 animals, we found stronger and more consistent stainings, as compared with evEx1 containing animals -Gal activity was still predominantly confined to the touch neurons, but a significantly higher proportion of larvae stained in the FLPs. PVD neuron staining was also detected in a proportion similar to the FLPs (identities of these cells to be confirmed). mec-7 may therefore be expressed in the exact same subset of neurons as mec-3 (this raises the question as to why 15- protofilament microtubules are not found in the FLPs or the PVDs). Second, and most importantly, the mec-7-lacZ gene expression is greatly reduced in some newly tested mec-3 mutants. We have transferred jeIn1 into the genetic background of 5 more mec-3 alleles ( sent to us by Shohei Mitani). Table 1 shows the results of the X-Gal stainings of these mec-3 transgenics: there is a global decrease, of a similar amplitude in all cells, of mec-7 expression. This decrease is more pronounced in some alleles. This suggests that some alleles of mec-3, in particular u298, are somehow leaky, while others, such as u6 are more severe (but not null?). In the light of these results, the possibility that the mec-3 protein directly activates mec-7 transcription remains a strong one. [See Figure 1]