Worm Breeder's Gazette 9(3): 29

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.

Burrowing, Spontaneous Mutants, etc. with Another Wildtype Strain

R. Cassada

The wildtype strain of C.  in Freiburg (Fbg 
1A, available from the CGC as RC301) is a typical high-copy number 
strain with a mutator activity. I have been looking at its biology 
recently with the goal, shared with others, of obtaining transposon-
insertion embryonic lethal mutations. Burrowing seen here appears to 
occur as a consequence of the accumulation of feeding animals of all 
ages on the thickened edge of the lawn (I call this propensity 
'bordering'), followed by mechanical wearing down of the agar locally, 
leading finally to burrowing itself (and a tendency to stay under the 
surface). Bordering arises without any reduced motility, as compared 
to N2 on a lawn. N2 borders on an old lawn, where only the edge still 
has healthy, growing bacteria. On a very fresh, thin lawn Fbg does not 
prefer the border, as it is not thicker than the rest of the lawn, but 
like N2, chemotaxes nicely to such a lawn and disperses uniformly on 
it. Even just hatched Fbg worms tend to clump with each other, as N2 
does in the swarm-stage on old plates, suggesting an enhanced 
sensitivity to some 'pheromone' as well. Both bordering and clumping 
are single-animal autonomous responses, as seen with morphologically 
marked mixed populations. Single-animal assays on 1/2' diameter day-
old lawns show 90% of the tracks (and eggs if any) of mutant animals 
on the lawn s edge, vs 10% for N2. Jarring the plate may activate 
bordering animals to leave the edge briefly, while remaining on the 
lawn. Bordering is dominant in Fbg/N2 heterozygotes, suggesting N2 has 
lost this function (as proposed by Hodgkin et al, WBG 8, Nr. 3, 36). 
There are no maternal effects on bordering or nonbordering, nor is 
epistasis by other mutations detectable, as long as chemotaxis to the 
lawn is normal. Bordering is due to a single X-linked gene (proposed 
name:bor-l), mapping about 20% from lon-2 and 3% from unc-7 (maybe 
near osm-l?). Efforts are being made to isolate spontaneous non-
burrowers. To reduce burrowing, besides using 3% agar, as recommended 
by Leon Avery (WBG 9, Nr.l, 88), retard bordering by using a richer 
medium (such as Avery s or 5x peptone), since the lawn edge thickens 
later, or by seeding a whole-plate lawn (no border!). Wildtype Fbg 
also has an autosomal dominant mating plug allele, presumably plg-1 (
Hodgkin et al, op.cit.). Plug formation depends only on the male 
genotype, showing no maternal effects (plg/N2 mutant males plug even 
if their mother was N2) or 'uxorial' effects (mutant males plug even 
if their mates are N2). Besides lots of somatic mutants and sick 
animals, many visible Fbg mutants have been found, roughly as 
frequently as with Bergerac B0. My screen for emb mutants involves 
looking for 'baggie' adults with unhatched eggs inside after leaving 
them in nicotine solution (without any vul- mutation). Screening 
single worms on plates (no nicotine) has revealed the complication 
that at a certain age a Fbg adult may begin to produce dead embryos, 
suggesting massive activation of Tc1 in the ovary, but give no mutants 
among the earlier, viable progeny. One of several real emb mutants 
isolated has slow embryonic cell divisions. So far, I have no 
revertant of any spontaneous Fbg mutant.