Worm Breeder's Gazette 14(1): 49 (October 1, 1995)
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.
Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114 USA
Mutations in dig-1 (n1321 and n1480 ) were originally isolated due
to their displaced gonad phenotype, their gonad often being anterior or
dorsal. Even when the dig-1 gonad is correctly positioned, it is easily
displaced by mechanical force, unlike the N2 gonad (M. Basson, personal
communication). We found five new dig-1 alleles in screens for various
sensory mutants. Two alleles (n2467 and nu52)were isolated as nose touch
insensitive mutants [WBG 12(3): p. 105; A. Hart and J. Kaplan, unpublished
results]. Electron microscopy of n2467 revealed defects in CEP, OLQ, AWC,
and AFD sensory endings. In addition, the n267 cuticle in the buccal
cavity fails to adhere to the pharyngeal epithelial cells [WBG 12(3):105].
Based on these results, we suggested that dig-1 is required for adhesion
in several tissues of the worm.
We have now isolated three new alleles (nu319ts, nu336, and nu345)
using a morphological screen for defects in the IL1 and the IL2 sensory
processes (WM 1995, p. 447). IL2 neurons were stained with DiO/Calcium
acetate (C. Bargmann, pers.comm.) while IL1 neurons were visualized by
expressing anunc-5::GFP transgene (as an array), which is expressed in the
IL1 neurons (kindly provided by J. Culotti). All 7 dig-1 alleles show
defects in the position of sensory processes. The defects in the IL1's
and IL2's are similar; sensory processes often follow aberrant paths to
the worm's nose, sometimes branching abnormally. IL1 sensory processes
often do not reach the tip of the worm's nose; this may also be true of
IL2 sensory processes, but such aberrant processes would not be visualized
by the DiO assay, as the processes must penetrate the worms cuticle to
pick up the dye. The IL1 and IL2 axons usually project to the nerve ring
normally.
We are currently characterizing the dig-1 alleles with respect to
both their gonad and sensory process phenotypes. dig-1(nu336) is the most
severe of the 7 dig-1 alleles. While all other dig-1 alleles are quite
healthy and fertile, nu336 animals have very small broods, are somewhat
Unc, and have the mose severe sensory ending defects. The unc-5::GFP
array in nu336 has integrated and co-segregates with the Dig-1 phenotype,
suggesting that the array may have caused the mutation by integrating into
dig-1. We are currently testing this hypothesis. dig-1(nu319ts) is the
weakest allele; even at 25o C, the sensory process defects are impenetrant
and vary greatly in severity. nu319ts has no obvious gonad defect (by
dissecting scope observations). Preliminary experiments indicate that the
temperature sensitive period for the sensory ending defects is embryonic.
Other dig-1 alleles appear to fall between nu336 and nu319 in severity,
but have yet to be fully characterized.
dig-1 is very close to sma-3 on the cluster of LGIII. Two
candidate genes in the region (sequenced by the genome consortium) are a
worm homolog of tenascin, an ECM molecule involved in adhesion, and a very
large gene (>40 kb) with homologies to cell adhesion molecules N-CAM and
L1. We are currently testing whether these genes correspond to dig-1.