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.
|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.