Worm Breeder's Gazette 13(4): 92 (October 1, 1994)
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.
Ilan Zipkin Cynthia Kenyon
Department of Biochemistry University of California, San Francisco, CA
94143-0554
We are primarily interested in the genetic and molecular control of directed cell
migration. Towards this end, we have been looking for mutants defective in the early
embryonic long-range migration of the M mesoblast, which is born in the anterior of
the embryo (near the future mid-pharynx) and migrates by the comma stage to just
posterior to the gonad. Only one mutation to date has been published which affects the
migration of M, that is unc-39 ( ct73 , e257 , rh72 )V(Manser and Wood, l990 ).To
facilitate screening for additional M migration-defective mutants we decided to
visualize M using a GFP (Green Fluorescent Protein, thanks to Marty Chalfie) reporter
construct. This construct (m uIS16 ;courtesy Craig Hunter) is driven by the mab-5
promoter and has been shown to be expressed in M until at least mid-L1. It is hoped
that screening for a fluorescent cell in the anterior of newly-hatched larvae will be a
convenient way to isolate more M migration mutants. Preliminary screening (of only
600 F1 clones) has in fact identified one new mutant, which exhibits a very low
penetrance M migration defect.
As a test for the premise of this screen, we examined larvae of the genotype
unc-39 ( ct73 );m uIS16 to see what a fluorescent M in the anterior would look like.
Manser and Wood (1990) reported that M is in an abnormal location 61% of the time in
ct73 .By GFP visualization, we find that number to be slightly low; in our hands M is
anteriorly misplaced in approximately 80% of all L1 sseen. M can end up anywhere
between the posterior pharynx and V3 when misplaced. In addition, we find that M
exhibits an abnormal morphology in unc-39 ( ct73 );m uIS16 .In wild-type, M is a fairly
large cell with a regular, rectangular shape and smooth edges. In contrast, in unc-39
( ct73 );m uIS16 M has a variable, irregular cell shape, with multiple, filopodia-like
extensions often extending quite far both anteriorly and posteriorly. These extensions
look almost axonal, and in general M appears "stretched out". (See Figures for a
typical example) Sample pictures will also appear on the WWW site
"http://wormworld.ucsf.edu/" as they become available.
To further investigate this phenomenon, we looked at several mutants by GFP
and scored M's position and morphology. In the wild-type m uIS16 background, M
had a normal position and morphology in all but one of over 200 L1 sscored. In unc-39
( ct73 );m uIS16 ,M had an abnormal morphology in over 90% of animals scored,
whether it was in the correct position or not. M was also seen to have an abnormal
morphology in 11/40 L1 sof the genotype mab-5 ( e2088 )III;m uIS16 ( mab-5 being the
worm HOM gene related to Antennapedia), and in two of these cases M was anteriorly
displaced. It is possible that there is some linked mutation in the m uIS16 background
which potentiates this morphology defect, however M is significantly affected in both
mab-5 and unc-39 .Finally, in the new mutant, M has a normal morphology even
when anteriorly displaced, further demonstrating that these characteristics are
genetically separable.
