Worm Breeder's Gazette 11(5): 82

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.

Expression of mab-5 Under the Heat Shock Promoter Mimics the Effect of a Putative mab-5(gf) Mutation on the Q Neuroblast Migrations

Stephen Salser and Cynthia Kenyon

Figure 1

The Q cells are migratory neuroblasts born in symmetric positions on 
the left and right sides of the animal.  Although they divide 
identically on the two sides, they migrate asymmetrically such that 
the descendents of QR are found in the anterior, whereas the 
descendents of QL are found in the posterior.
Previous work has shown that there are at least two stages to this 
migration.  Before the first division, QR migrates anteriorly to 
assume a position just above V4, while QL migrates posteriorly to a 
position above V5.  This phase of the migration is unaffected by 
mutations in mab-5.  Following the first division the cells begin a 
more complex pattern of migration.  QR.a, QR.p, and their descendents 
continue the anteriorward migration, QL.a and its daughter, QL.ap, 
continue to migrate posteriorly, and QL.p and its descendents remain 
stationary.  Loss-of-function mutations in mab-5 cause the daughters 
of QL to behave like the daughters of QR, whereas the putative gain-of-
function allele e1751 causes the reverse transformation.
[See Figure 1]
Expression of a mab-5 cDNA under the worm hsp16.1 heat shock 
promoter mimics the e1751 phenotype.   In these experiments the mab-5 
cDNA was inserted into a HpaI site in the second exon of hsp16.1(
generously sent to us by Peter Candido.)
This construct was injected along with the unc-31 cotransformation 
marker into mab-5(e2088);unc-31(e169) hermaphrodites, and heritable, 
unstable lines were obtained.  Non-Unc animals were examined starting 
one hour after hatching and heat shocked on the agar pad (30 minutes 
at 31 C) just before the first division of Q.  In control animals that 
are unshocked or lack the construct, the descendents of both QL and QR 
migrate anteriorly as expected in an e2088 background.  Eight heat-
shocked worms that carry the construct were examined on the left side. 
QL.a migrated posteriorly over QL.p (7/8 animals), QL.ap migrated 
posteriorly into the tail (6/8 animals), and QL.p and QL.pa remained 
stationary (8/8 animals).  Although no lineages have yet been obtained 
for the right side, the QR.paa and QR.ppp cells were found near V4 
where QR.p is born (8/8 animals).  From this we conclude that mab-5 
transcription is necessary and sufficient to 
1 ) Q.a and Q.ap migrate posteriorly rather than anteriorly.
2) Q.p and Q.pa remain stationary rather than moving anteriorly.
We were interested in whether Q.ap migrates posteriorly as a direct 
effect of mab-5 activity or simply because it is now born close to its 
new destination in the tail.  To address this issue we allowed Q.a to 
migrate anteriorly past ALM before heat shocking the animals.  In 2/2 
sides examined Q.ap migrated posteriorly, in one case from V1 back to 
V3, in another from V3 back to V6.  From this we conclude that mab-5 
activity is sufficient the make Q.ap migrate posteriorly even if it is 
born near the head.
By carrying out the heat shock at later times in development we have 
also observed mab-5 activity in the P, V, and M lineages.  Heat shock 
in L3 leads to the production of ectopic rays similar to those seen in 

Figure 1