Worm Breeder's Gazette 9(3): 94

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.

More News About glp-1

J. Austin and J. Kimble

Figure 1

Seven recessive alleles of the gene glp-1 have now been isolated 
using EMS mutagenesis, by both direct and complementation screens. 
Five of these seven alleles, including the two isolated by 
complementation, have the same phenotype; Z2 and Z3 divide a few times 
resulting in a small number of germ cells which then all enter meiosis 
prematurely and form sperm. This phenotype is completely penetrant and 
is the strongest that we have seen for mutations in this gene (in the 
other two alleles, Z2 and Z3 go through a greater number of divisions 
before entering meiosis). The strength of this phenotype and frequency 
of mutations with this phenotype suggest that it may be the null 
phenotype of glp-1We have begun a mosaic analysis to determine in 
which cell(s) the gene product is required for wildtype germline 
development. An unstable free duplication was created by gamma-ray 
mutagenesis of mnDp37 provided by Bob Herman. The new duplication, 
qDp3, has breakpoints between dpy-17 and ncl-l on the left and between 
glp-1 and unc-69 on the right. Because qDp3 covers the gene ncl-l, we 
have been able to make use of the cell autonomous nature of the 
phenotype of ncl-l(e1865) as a marker for the presence or absence of 
the duplication, as suggested by Ed Hedgecock (WBG 9(1),66-67.).
The strain we are using for this mosaic analysis is ncl-l(e1865)unc-
36(e251)glp-1(q46)III;qDp3.   The unc-36 phenotype depends on the 
presence or absence of the wildtype unc-36 gene product in the AB.p 
lineage (Kenyon,C. Cell 46, 477-487.). Therefore, by screening for 
animals which are nonUnc but which are Glp it is possible to isolate 
mosaic animals in which the duplication has been lost in cells that 
require the wildtype glp-1 gene product for normal germline 
development. These nonUnc Glp mosaics are then screened, by Nomarski, 
for the presence of the Ncl phenotype to determine where the 
duplication has been lost. Because the distal tip cells are known to 
play an important role in the development of the germ line, we thought 
it most likely that the wildtype glp-1 gene product would be required 
in either the distal tip cells or in the germ line. For this reason, 
we have concentrated on looking for duplication losses in cells 
descended from Pl.
Our preliminary results are shown below. For each nonUnc Glp animal, 
the presence or absence of qDP3 in the MS, C and D lineages was 
determined by scoring the Ncl phenotype of body wall muscle cells 
derived from these embryonic precursors. In the case of MS the sheath 
cells and distal tip cells of the somatic gonad were also scored when 
possible (in some animals only one distal tip cell nucleus could be 
clearly observed). Because of the nonUnc phenotype of these animals it 
was assumed that the duplication was present in at least some of the 
cells derived from AB. The nonUnc Glp animals examined so far fall 
into six classes based on their pattern of duplication loss. It should 
be pointed out that in one group of animals (class VI) no Ncl nuclei 
were observed. Such animals could be the result of a recombination 
event between the duplication and the chromosome or they may have lost 
the duplication in a tissue which could not be scored. For example, 
because the nonUnc Glp animals are sterile, it is not possible to test 
directly for the presence of qDp3 in the germ line.
So far, the results suggest that glp-1 acts in the germ line. The 
presence of qDp3 in MS in the animals in class II indicates that the 
presence of the glp-1 wildtype gene product in the somatic gonad is 
not sufficient for normal germline development. In each of these 
animals sheath cells in both gonadal arms and at least one distal tip 
cell were scored and all were Ncl+. In addition, a mosaic animal has 
been found (class VII) in which the anterior distal tip cell is Ncl 
but germline development appears to be normal in both gonadal arms. 
Thus, the wildtype glp-1 gene product in the distal tip cell is not 
necessary for normal germline development. A large number of mosaic 
animals (classes I, II and III) were found in which qDp3 is absent in 
D. Because the D lineage generates only body wall muscle cells, we 
think it likely that, in these animals, qDP3 has been lost in P3 or 
before and that it is the absence of the wildtype glp-l gene product 
in the germ line which is causing the abnormal germline development. 
In two animals (classes IV and V) there is no evidence of a 
duplication loss in the divisions leading up to the formation of the 
germ line. Because many of the animals we have observed appear to have 
had more than one duplication loss our working hypothesis is that, in 
these animals, an additional, undetectable, duplication loss has 
occurred in the germ line. Alternatively, the glp-1 gene product may 
be required in other tissues in addition to the germ line and we are 
currently testing 
possibility.{Figure 1}

Figure 1