Worm Breeder's Gazette 8(3): 65

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 Actin Genes of C. elegans

M. Krause, D. Hirsh

We have continued to look at transcription of the actin genes during 
C.  elegans development both in wild-type worms and revertants of 
actin mutants.  We now have gene-specific probes for all four genes.  
Using these probes in conjunction with improved Northern sensitivity 
we have determined the post-embryonic pattern of actin gene 
transcription.  Some of these results contradict results reported in 
an earlier Newsletter.
In wild-type worms all four actin genes are transcribed and the 
level of transcription does not appear to fluctuate during post-
embryonic development.  Three size classes of transcripts of 1450, 
1550 and 1650 nucleotides are made from the four genes.  The 1450 size 
class is comprised of transcripts from genes 1 and 2; the 1550 and 
1650 size classes are comprised of gene 3 and gene 4 transcripts 
respectively.  We have not extensively quantitated the abundance of 
the transcripts from each gene but it appears that gene 1, 3 and 4 
transcripts are comparable in abundance.  Gene 2 transcripts are 
clearly the least abundant.
We have started to look at embryonic and tissue-specific 
transcription using in situ hybridization to whole worms.  Preliminary 
results have failed to localize transcripts from any of the genes to a 
specific tissue or embryonic stage.  As a control we have localized a 
yolk protein gene probe (provided by Tom Blumenthal) to the intestinal 
cells of appropriately staged worms under the same hybridization 
conditions.  We are working on improving the resolution of the in situ 
We have analyzed the post-embryonic transcription of the actin genes 
in three revertants of actin mutants in which reversion was 
accompanied by rearrangement in the actin gene cluster.  As reported 
before, the three revertants have transcriptional patterns that differ 
from those seen in wild-type worms.  Although we have identified the 
transcripts in each case, a correlation between the physical 
arrangement of the genes and the effect on transcription is not 
straightforward.  For example, RW2458, which has a 500 bp insertion in 
the gene 1 region, has a detectable gene 1 transcript although greatly 
reduced in abundance.  This transcript is identical in size to the 
wild-type transcript.  This revertant also has an additional actin 
transcript about 600 nucleotides long.  As we have not yet precisely 
localized the point of the insertion event relative to the coding 
region of the gene, it is difficult to interpret these results.  We 
are currently cloning the rearranged regions from the revertants in 
order to define the exact structure of the rearrangements in the hope 
that it will allow us to say something more profound about the 
developmental regulation of these genes.