Worm Breeder's Gazette 9(2): 90

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.

Acetylcholinesterase Activity and Dosage Compensation

P. Meneely and K. Nordstrom

The structural gene for one form of acetylcholinesterase is the X-
linked gene ace-1; the activity of the ace-1 encoded enzyme can be 
readily distinguished from other forms because it is resistant to 
deoxycholate (Johnson, et al.  Genetics 97: 261-279).  The assays are 
extremely easy and can be carried out on a single worm.  Duckett and 
Russell have shown that the dosage of ace-1 is compensated, although 
the results were complicated by an apparent influence of sexual 
morphology on enzyme activity.  We are using the level of ace-1 
activity as an additional measure of X-chromosome expression in 
studying dosage compensation.
Under a standard set of conditions (final substrate concentration of 
2X10+E-6 M, specific activity 296 mCi/mmol, assayed for 24 hr--
basically the conditions used by Johnson et al.) and with assiduously 
chosen well-fed worms at about the same age, the level of total 
activity in N2 hermaphrodites varies by less than 10% (average 19,700 
cpm).  The activity shows linear dependence on time, substrate 
concentration, and the number of worms included in the assay.  The DOC-
resistant activity is about 60% of this; again the amount of variation 
between assays is small.  We find, agreeing with Duckett and Russell, 
that N2 males have a slightly higher total activity than 
hermaphrodites, but this difference may not be significant.  We have 
not yet compared X0 hermaphrodites with XX hermaphrodites to eliminate 
sex-dependence, but the differences we see are within the range of 
between sample variance.
With the assay working reproducibly, we are now looking at some of 
the dosage compensation mutants and aneuploid strains that we have 
tested previously using our genetic assay.  dpy-21 hermaphrodites are 
25-30% higher in total activity than N2, and most if not all of this 
difference is due to elevation of ace-1 activity; the ranges of 
variation among dpy-21 samples and N2 samples do not overlap, which 
indicates this is a real difference.  dpy-21 mutants also have a 
higher level of X expression than wild-type by both the genetic assay 
and several molecular assays relying on transcription from X-linked 
clones.  The other mutants tested have been more variable, probably 
due to sickliness of the strains.  We will try to reduce the effect of 
this sickliness by using staged larvae; preliminary results are that 
this approach will help.  One curious result is that level of total 
activity in a 3X strain is not significantly higher than the 
comparable 2X strain.  By the genetic assay, 3X animals had higher X 
expression, but perhaps acetylcholinesterase levels are subject to 
additional controls in aneuploid strains.