Worm Breeder's Gazette 10(2): 56

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.

New Maternal Mutations Affecting Intestinal Development

Diane Morton, Michael Roos and Ken Kemphues

We are screening for maternal effect lethal mutations that may 
identify genes important for determination or differentiation of 
intestinal cells in C.  elegans embryogenesis.  Specifically, we are 
looking for mutants in which the arrested embryos possess more than a 
hundred cells, but show no detectable gut granules under polarized 
light.  (WBG 9[2] 74, 1986; C.  elegans meeting abstracts 1987, 3).  
We have identified 36 such mutants among recent screens of 
approximately 12,000 F1s from EMS mutagenized egl-23(n601) 
47) animals.  We find that about 15% of the F1s 
carry a maternal effect lethal mutation; among these Mel mutants, 
approximately 2% produce embryos lacking gut granules.  Our previous 
work with par mutants suggested that failure to produce gut granules 
during embryogenesis could result from mutation in the genes par-1 and 
par-4.  In fact, among the 36 new gut granule mutations, we have 
identified 5 par-1 alleles and 7 par-4 alleles.  The remaining mutants 
do not appear to have partitioning defects in the early cleavages.  
Apparently, par-1 and par-4 are the only par genes that can mutate to 
give a complete failure of intestinal cell differentiation.  Most of 
the remaining mutants produce embryos with about two hundred cells, 
without obvious cell differentiation.  Such mutants may not be gut-
specific; other cell types that would normally differentiate later in 
development may also be affected.  The most interesting mutants for 
our analysis are those in which the embryos contain many other 
differentiated cells, but no detectable gut differentiation.  In these 
mutants a lack of gut granules could be due to a defect specific to 
the intestinal cell line.  We have found two kinds of such interesting 
mutants -- one mutant, it77 X, produces embryos that undergo 
morphogenesis to produce abnormal-looking larvae that lack gut 
granules.  We have not yet examined this mutant carefully for specific 
anatomical defects.  Four other mutants produce embryos with a 
terminal phenotype similar to par-1 and par-4; the embryos arrest as 
amorphous masses of many differentiated cells, but no gut granules are 
detectable.  These mutants show a normal early cleavage pattern, and p 
granule staining of one of them showed a normal distribution.  We do 
not yet know whether the mutations in this class represent one or 
several loci.  (Perhaps these mutations identify a gene(s) that 
encodes a cytoplasmic factor that must be partitioned by the maternal 
partitioning system to the E line in the first cleavages???) While 
performing these screens, we also noticed a class of maternal effect 
lethal mutants in which only a few of the embryos had gut granules, 
and all of the embryos arrested as masses of differentiated cells.  
Because this phenotype is characteristic of known par-2 mutants, we 
also saved this type of mutant, and found 8 that have a par-2-like 
early cleavage pattern.  Five of these thus far have been confirmed as 
new alleles of par-2 (Niansheng Cheng, personal comm.).  We also 
isolated two other mutants with par phenotypes (synchronous and 
symmetric early cleavages) that are not par-2-like, and which we have 
not yet assigned to complementation groups.  One of these mutants has 
an early cleavage pattern similar to par-1 [some par-1 mutants produce 
a low frequency of embryos with gut granules (Betty Suh, and our own 
observations)].  The other mutant does not map to LG IV,V or X, which 
rules out pars-1,4,5.  This mutation may represent an unusual allele 
of par-1 or par-2, or could identify another gene that can mutate to 
give a par-like phenotype.
Screens for maternal effect lethal mutants with a characteristic 
terminal embryonic phenotype appear to be efficient for identifying 
mutations in par genes.  By this method we have more than doubled the 
number of par-1, s.  The 
frequency with which we have found these new Dar mutations suggests 
that they are typical for these genes, and are likely to represent 
loss of function or reduced activity of the gene product.  We did not 
identify mutations in the genes par-3 or par-5 in our screens.  Both 
of these mutants produce a greater proportion of embryos containing 
gut granules than the other par mutants and so would not be picked up 
in these screens.  However, screens for mutants with terminal 
embryonic phenotypes characteristic of either par-3 or par-5 should be 
feasible.  In fact, we have isolated one new par-3 mutation in this