Worm Breeder's Gazette 10(3): 101

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Isolation and Characterization of Grandchildless Mutants in C. elegans

Paula Martin, Carol Garvin and Susan Strome

Figure 1

Several types of embryo manipulation experiments suggest that cell 
fates are specified in early C.  elegans embryos mainly by internally 
segregated maternal factors.  The defects in intestinal cell 
differentiation and germ-line development observed in some of the par (
for partitioning) mutants strengthen this view for the intestine and 
germ-line (Kemphues et al.  Cell 52, 311-320, 1988).  We have begun 
screening for mutations in the maternal factors required for 
development of the germ line.  We are screening for maternal effect 
sterile (mes) or grandchildless mutants by looking among EMS-
mutagenized worms for the production of sterile progeny in the F3 
generation, as shown 
[See Figure 1]
We expect to identify at least 2 classes of mutants 1) par mutants 
and 2) germ-line determinant mutants.  One mes locus, identified by 
the two mutant alleles, bn7 and bn24, exhibits par like qualities.  
Both alleles are strict maternal effect and, like Dar-2(e2030), are 
leaky -- homozygous bn7 and bn24 hermaphrodites produce some fully 
fertile and some sterile, agametic progeny.  Similar to par-2(e2030), 
some embryos from bn7 and bn24 hermaphrodites show aberrant 
partitioning of germ-line P granules to somatic founder cells during 
the divisions of P2 and P3 -- we do not know whether the mis-
distribution of P granules leads to sterility.  There is some 
elevation in lethality of the embryos produced by bn7 and bn24 
hermaphrodites, especially at 25 C -- 14% lethality for bn7 embryos 
compared to 6% for N2 embryos and 45% for par-2(e2030) embryos at 25 C.
bn7 and bn24 are not alleles of the known par loci -- they map to 
the X chromosome, in the vicinity of lin-2 and unc-9.  (Careful 
mapping is in progress - any new markers in the region would be 
greatly appreciated!) Two other par-like mes mutants are currently 
being mapped and analyzed.
The mes mutant, bn11, is a good candidate for a germ-line 
determinant mutant.  It is a strict maternal effect mutant that 
produces 100% sterile, agametic progeny.  P granules are segregated 
normally in embryos from bn11 hermaphrodites -- thus there is no 
apparent partitioning defect.  However, embryonic lethality is 
somewhat elevated (12%) at 25 C.  bn11 maps to LGII, approx.  18 map 
units to the right of unc-4, probably out in the big bare zone between 
rol-1 and unc-52 (again, any new markers on the right arm of LGII 
would be welcome) - LGII does not contain any of the known par loci.  
In addition to bn11, one other fully penetrant mes mutant is being 
mapped and analyzed.

Figure 1