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.
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.