Worm Breeder's Gazette 11(5): 41

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myo-2 Contains Both an Enhancer and a Promoter Specific for Pharyngeal Muscle

Peter Okkema and Andrew Fire

Figure 1

myo-2 encodes a myosin heavy chain isoform expressed specifically in 
pharyngeal muscles.  We have been analyzing myo-2 regulatory regions 
using lacZ fusions.  Our experiments have been done by examining  -gal 
expression in L3-adult F1 progeny of injected hermaphrodites.
We have identified an enhancer in a 227bp EcoRI-RsaI fragment 
located about 670bp upstream of the myo-2 translational start site (
ATG).  When inserted upstream of a glp-1/lacZ fusion, this enhancer 
induces  -gal activity almost exclusively in the pharyngeal muscles (a 
small number of animals (<4%) also express  -gal in 1-3 large nuclei 
near the anus; we have not characterized these cells further).  The 
glp-1/lacZ fusion alone is not expressed.  Therefore, the myo-2 
enhancer appears almost completely specific for pharyngeal muscles.  
Consistent with this result, both myo-3/lacZ and CeMyoD/lacZ fusions, 
which are normally active only in body wall muscle, are expressed in 
pharyngeal and body wall muscles when placed downstream of the myo-2 
myo-2/lacZ fusions lacking the enhancer are also expressed in 
pharyngeal muscle.  Thus, there are at least two independent 
pharyngeal specific regulatory elements upstream of myo-2.  This 
downstream element has been localized to 250bp NarI-PvuI fragment just 
5' to the ATG translational initiation codon.  It does not act as an 
independent pharyngeal enhancer when inserted upstream of the myo-3 
promoter.  Rather, this element behaves as a pharyngeal muscle 
specific promoter.
myo-2 regulation is analogous to that of unc-54 (Fire and Harrison, 
WBG11,2,p.22).  In that case, a body wall specific element just 
upstream of the promoter acts only very weakly as an enhancer, while 
an internal element 1kb downstream acts independently as a strong body 
wall muscle specific enhancer.
We are currently defining the pharyngeal muscle regulatory sequences 
more precisely and plan to identify trans-acting factors interacting 
with them.
[See Figure 1]

Figure 1