Worm Breeder's Gazette 13(5): 29 (February 1, 1995)

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.

CeMEF-2 Is Expressed in Muscle and Nerve.

Morgan Park1, Daryl Dichoso2, Rey Lee-Llacer1, Robert Littlejohn1, Michael Krause1

1 Laboratory of Molecular Biology, NIDDK, NIH.
2 Dept. of Biology, University of Houston.

The vertebrate Mef-2 family of genes encodes sequence
specific transcription factors of the MADS box class that
are related to the serum response factors (SRFs). Mef-2
genes are expressed in a variety of tissues, however, their
expression in muscle has received the most attention.
In vertebrates, MEF-2 isoforms play a critical role in
activating a variety of muscle specific proteins during
skeletal muscle differentiation, including a positive
feedback regulation of MyoD family members such as MyoD
and myogenin. In addition, certain MEF-2 isoforms are
expressed in differentiating cardiac tissue and can activate
cardiac-specific genes. In Drosophila, there appears
to be only a single Mef-2-like gene that is expressed in
precursors of all muscle types, with expression in striated
muscle preceding that of the MyoD family member, nautilus;
essentially no neuronal expression has been observed
in flies.
We have cloned a C. elegans member of the Mef-2 family by
degenerate RT-PCR. PCR results were previously interpreted
to suggest as many as five Mef-2-like genes might exist
in the worm. However, genomic and cDNA library screens
continue to pull out only a single gene. A careful re-examination
of the PCR data has allowed us to eliminate (due to suspected
PCR errors or contamination) all but a single product from
C. elegans, consistent with a single gene. Genomic Southern
blots also suggest a single gene, although there is a faintly
hybridizing secondary band that can not be explained by
the genomic locus we have cloned.
We have looked at a single line of animals transformed with
a CeMEF-2::beta-galactosidase reporter construct that
includes ~7kb of sequence upstream of the ATG in addition
to a large (2337bp) first intron. During embryogenesis,
weak expression is seen at the tailbud stage in a few unidentified
cells in the head region. Subsequently, other cells begin
to express the reporter gene and by the three-fold stage,
there is very strong expression in what appears to be all
muscle cells (bwm, pharyngeal, others?) and all neurons.
The large number of staining cells makes it difficult to
determine if all minor muscle cell groups (intestinal,
uterine, etc.) are expressing. Expression continues
in both muscle and nerve to adulthood.
The expression pattern of this mef-2::1acZ construct
is similar to what is seen in vertebrates, suggesting that
this transcription factor is playing a role in the differentiation
of muscle and nerve in C. elegans. If the onset of expression
during embryogenesis is correctly reflected by our reporter
construct, it is unlikely that CeMEF-2 initiates the commitment
of precursor blastomeres to these different cell types
(eg. in body wall muscle cells, myosin heavy chain is activated
prior to our reporter construct). Instead, CeMEF-2 might
interact with other tissue-specific factors to enhance,
or maintain, the expression of activated genes and help
drive terminal differentiation.