Worm Breeder's Gazette 10(3): 76

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Transcription in Dauer Larvae

Brian Dalley and Miriam Golomb

We are interested in whether dauer larvae are transcriptionally 
active and if so, whether their pattern of transcription is distinct 
from other larval stages.  As previously reported (WBG 10:1, 74-75), 
dauer larvae nuclei are indeed active in run-on transcription by RNA 
polymerase II (RpoI), however, less active than nuclei from other 
developmental stages.  More accurate measurements have demonstrated 
that the rate of RpoII transcription (relative to nuclear DNA content) 
is essentially constant for nuclei isolated from all developmental 
stages except for dauer larvae.  In this stage, RpoII transcription is 
approximately 40% of the level observed for other developmental stages.
The rate of RpoII transcription is restored to the level associated 
with actively growing worms within two hours of placing dauer larvae 
on food.  Transcription of specific genes by dauer larvae was analyzed 
by allowing nuclei to incorporate [32P]-CTP in a nuclear run-on assay 
and hybridizing the RNA with dot blots of cloned genes.  Dauer nuclei 
were found to actively transcribe a number (of structural genes 
including actin, hsp-70 heat shock, ama-1, and collagen in addition to 
splice leader precursor.  However, where was a drastic reduction in 
transcription of histone and myosin .  Since metabolically, dauer 
larvae are relatively inactive, the question arises of whether 
transcription observed in isolated nuclei is really a reflection of in 
vivo patterns as opposed to the in vitro activation of dormant 
transcription complexes formed before entrance into the dauer stage.  
To address this question, we compared nuclear transcription with 
steady-state levels of message in dauer larvae, L3's and recovering 
dauer larvae (eight hours after return to food).  By Northern analysis,
equal amounts of heat shock message were found in all three stages; 
however, actin message was moderately reduced and histone message was 
completely absent in dauer larvae.  The RNA pattern in these stages 
resemble the transcriptional patterns of nuclei isolated from these 
stages.  This further suggests that dauer larvae are actively 
transcribing mRNA and that transcription in isolated nuclei is an 
accurate reflection of what is happening in vivo.