Worm Breeder's Gazette 13(4): 97 (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.

Update on deficiency screens

Joohong Ahnn Andrew Fire Carnegie Institution of Washington, Department of Embryology, Baltimore, MD 21210

We have been screening available chromosomal deficiencies in order to identify
genetic loci whose zygotic expression is required for early events in embryogenesis
including formation of body wall muscle cells (1). A surprising result of deficiency
screens (ours (1) and others (2, 3) has been the extensive tissue differentiation that
occurs in many of the deficiency homozygote embryos. In our initial analysis we found
only one region (on the left tip of LGV) which was required for accumulation of
body-wall myosin. This gazette article reports updates on our deficiency analysis.
Analysis of additional characterized deficiencies:
  Embryos homozygous for nDf3 (II) (4) and nDf4 (II) (4) arrest elongation before
comma stage (although a small fraction develop to the 1-1/2 fold stage). These embryos
form pharyngeal structures, have gut granules and stain with antibodies to unc-54
and myo-3 products. Deficiency sDf23 (IV) (5) homozygous embryos arrest before
comma stage, have gut granules but no pharyngeal structures; these embryos do not
show any movement but stain with both anti-myosin antibodies. nDf42 (V) (6)
homozygous embryos show an early arrest with no movement, no gut granules, and no
pharyngeal structures. Homozygous embryos from nDf17 (III) (4) and nDf19 (X) (7)
both arrest at 2-fold stage, show twitching movement, have gut granules, form
pharynx and stain with myosin antibodies (n.b. mapping data on ACEDB suggests
nDf17 and nDf19 could be compound deficiencies).
  Producing a bank of Dfs of VL:
  In order to isolate small deficiencies in the region of LG VL which appears to be
essential for myogenesis, gamma-ray induced mutagenesis has been conducted.
Mutagenized N2 males were crossed into unc-34 dpy-11 animals, and rare Unc
Non-dpy F1 progeny were cloned. Seven deficiencies have been isolated among 17,000
haploid chromosomes screened so far. Further mapping of these deficiencies by
physical and genetic means should allow us to narrow down the myogenic locus (or
loci) in the region.
  A very early zygotic requirement?
  In a more general screen for early arrest mutants, several very early lethals
linked on LG III have been isolated. These segregate a high fraction of dead embryos,
suggesting a chromosomal break or rearrangement. About l/4 of the embryos from
these strains show a characteristic very early terminal phenotypes. These embryos
have 200-250 nuclei, with no overt tissue differentiation. The embryos fail to stain with
myosin antibodies and do not have gut granules. Embryos from two of these strains
were observed with 4-D microscopy to look for defects during early embryogenesis.
The early cleavage pattern of early-arrest embryos look normal, but these embryos fail
to complete last 1-2 cell divisions. In some cases, nuclear divisions appear to complete
without subsequent cytokinesis. It is interesting to compare these terminal phenotypes
with those of emb-29 (V). emb-29 produces embryos with comparable numbers of
nuclei, but these embryos exhibit extensive differentiation (8). This suggests that the
putative chromosome III defect is not simply due to blockage or failure of cell divisions.
 1. J. Ahnn & A. Fire WBG 12: 2, 106 Genetics (137:483-498)
 2. F. Storfer-Glazer & W. Wood Genetics (137: 499-508)
 3. J. Zhu & J. Rothman '93 C. elegans Meeting (Abt. 497)
 4. I. Greenwald & R. Horvitz unpublished
 6. M. Hengartner & R. Horvitz unpublished
 7. V. Ambros & R. Horvitz unpublished
 8. R. Hecht et. al J. of Cell Science (87:305-314)