Worm Breeder's Gazette 14(5): 49 (February 1, 1997)
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.
| 1 | Dept. of Microbiology, University of Kansas, Lawrence, KS, 66045 |
| 2 | Dept. of Biology, Johns Hopkins University, Baltimore, MD, 21218 |
We have continued genetic studies on exc mutants, in
which the long hollow processes (canals) of the excretory
cell form large fluid-filled cysts. We previously
classified these mutants into five groups based on cyst
morphology: exc-2, exc-4, let-4, and let-653 mutants form
large septate cysts near the excretory cell body; exc-1 and
exc-5 mutants form extremely large septate cysts (often
visible via dissecting microscope) predominantly at the
shortened canal termini; exc-3, exc-6, and exc-8 mutants
show regional canal widenings and meanderings, and
occasional inappropriate extra branchings to form multiple
canal lumena; alleles of sma-1 exhibit a short, very wide,
unseptate canal. Finally, the lone exc-7 allele rh252
exhibits small cysts along the length of the canal,
terminating in a large group of tiny cysts.
We have now made double mutants of several of the genes
from various groups. Double mutants made of genes from
within any one group showed no increase in severity in canal
phenotype. For example, exc-2 (rh90) exc-4 (rh133) animals
showed no changes in cyst size or morphology compared to
rh90 or rh133 alone, and no increase in larval lethality.
Similarly, exc-6 (rh103) exc-8 (rh210) canals appeared no
shorter or more meandering than those of the single mutants,
and exc-1 (rh26) exc-5 (rh232) mutant canals had similar
cyst size and placement as the single mutants alone.
Doubles constructed with exc-7 (rh252) showed
interesting effects, however. exc-7 is epistatic to exc-6;
the double mutants showed no abnormal branchings, only a
series of small cysts along the entire canal length.
Perhaps not surprisingly, the large cysts of exc-2 and exc-4
are epistatic to exc-7. Most strikingly, the doubles exc-7
(rh252) sma-1 (e30) and especially exc-7 (rh252) exc-3
(rh207) show canal phenotypes different from that of the
single mutants; instead, these animals show large cysts near
the excretory cell body, like those of exc-4 mutants.
Finally, we have been unable so far to isolate doubles of
exc-7 (rh252) and either exc-1 (rh26) or exc-5 (rh232); this
could indicate that these mutants are lethal in combination.
Our previous ultrastructural data, along with
sequencing results from the labs of David Baillie (Jones &
Baillie, Mol. Gen. Genet. 248, 719-726, !95) and Judith
Austin (see McKeown, Patel, Praitis, and Austin, WBG 14 (2),
p. 83) suggest that the exc genes encode proteins necessary
for the proper placement of structural elements, both
extracellular and cytoskeletal, at the apical epithelial
surface. We believe that these new genetic results indicate
that the differing morphologies of the various groupings of
exc genes reflect different elements that interact with each
other to shape this surface; Exc-7 may play a central
position in these interactions.