Worm Breeder's Gazette 13(2): 34 (February 1, 1994)
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.
To determine the site of action of lin-36 (see preceding abstract), we conducted a genetic mosaic analysis. A strain of genotype lin-8 ( n111 ); dpy-17 ( el64 ) nc1 -1(1865) lin-36 ( n766 ) unc-36 ( e251 ); sDp3 (Ä)was constructed. unc-36 has a focus in AB.p. dpy-17 apparently has a hypodermal focus in AB.a, AB.p, and C. ncl-1 has a cell-autonomous focus and affects numerous cells. Two strategies were adopted to find mosaic animals. In one, mosaic animals of the L3 - adult stages were isolated on the basis of gross morphology and then observed using Nomarski optics to confirm and further define the site of the duplication loss. Unc non-Dpy animals result from duplication loss in AB or AB.p. Dpy non-Unc animals result from loss in P1 , P2 ,or C (the progeny segregated allow a loss in P2 to be distinguished from a loss in C). Semi-Unc non-Dpy animals are the result of a loss in either AB.pl or AB.pr. The other strategy used was to examine seemingly wild-type L3 and L4 animals for the Ncl phenotype directly using Nomarski optics. This approach allowed us to identify AB.a losses. The Ncl phenotype was scored primarily in neurons. (We did not score the Pn.p cells because their Ncl phenotype is difficult to see.) From P1 ,the pharyngeal neurons I4 , I6 , M4 ,MS, and M1 ,the tail neurons PVR and DVC, and occasionally hyp11 were scored for the Ncl phenotype. From AB.p, the HSNs, and AB.p-derived neurons from the nerve ring and the tail were scored. From AB.a, the BDUs, ALMs, the pharyngeal neurons IS, MI, M2 s,and M3 s,and the AB.a-derived neurons of the nerve ring were scored.
The following data were gathered as controls. Meiotic loss in the strain was 31%, (n=771). Animals of phenotype non-Unc non-Dpy Muv occurred at 1.3% (n=531). The Muv phenotype occurred in 69% (n=240) of Dpy Unc animals (meiotic loss). Note that this last number sets an upper limit on the fraction of Muv animals we expected from a mitotic loss of the duplication in the lineage from which the cellular focus of lin-36 is derived.
Our results are tabulated in the figure below. Loss in AB, AB.p, AB.pl, or AB.pr often produced Muv animals. Loss in P1 or in AB.a failed to result in Muv animals. These data are consistent with an anatomical focus in both the AB.pl and AB.pr. lineages. The Pn.p cells derive from both of these lineages.
Three double losses were observed. One occurred in AB and MS/EMS and resulted in a Muv phenotype, presumably because of the AB loss. Another occurred in AB.pl and C resulting in a Muv phenotype, presumably because of the AB.pl loss. A third occurred in AB.prapp and AB.a resulting in a Muv phenotype, presumably because of the AB.prapp loss. Thus, the phenotypes of mosaic animals with double losses could be explained on the basis of one of the two losses.
The simplest interpretation of these results is that lin-36 acts cell-autonomously in the Pn.p cells, although it is possible that lin-36 is actually required in close relatives of the Pn.p cells, possibly hyp7 cells, in both the AB.pl and AB.pr lineages.
These lin-36 mosaic data are in marked contrast to the mosaic data for lin-15 .Bob Herman and Ed Hedgecock (Nature 348:169-171, 1990) showed that lin-15 acts cell-non-autonomously in a genetic mosaic analysis experiment. Specifically, they found that loss of lin-15 (+)in P1 AB or AB.p, AB.pl, or AB.pr can result in a Muv phenotype. hyp7 ,which derives from these lineages, was postulated to be the anatomical focus of lin-15 activity. Based upon these two results, we believe that the class B synMuvs encode components of a signaling system, some of which act in the hypodermis and some of which act in the Pn.p cells.