The MADS-Box Factor CeMEF2 Is Not Essential for Caenorhabditis elegans Myogenesis and Development

Abstract

MEF2 is an evolutionarily conserved MADS (MCM1, Agamous, Deficiens, and serum response factor) box-type transcription factor that plays a critical role in vertebrate and Drosophila melanogaster myogenesis. We have addressed the developmental role of the single MEF2-like factor, CeMEF2, in Caenorhabditis elegans. Using expression assays and two mef-2 deletion alleles, we show that CeMEF2 is not required for proper myogenesis or development. Moreover, a putative null mef-2 allele fails to enhance or suppress the phenotypes of mutants in CeMyoD or CeTwist. Our results suggest that despite its evolutionary conservation of sequence and DNA binding properties, CeMEF2 has adopted a divergent role in development in the nematode compared with Drosophila and vertebrates.

Defining the transcriptional redundancy of early bodywall muscle development in C. elegans: evidence for a unified theory of animal muscle development

“…In vertebrates, MEF-2 acts with the MRFs to regulate skeletal muscle differentiation (Black and Olson 1998;Tapscott 2005). In contrast, C. elegans mef-2-null mutants are viable and phenotypically normal with no known bodywall muscle defects (Dichoso et al 2000). We show here that this is because UNC-120/SRF acts with HLH-1 to drive myogenesis in the nematode, eliminating the need for MEF-2.…”

“…Whereas a subset of MRFs appears to be both necessary and sufficient for vertebrate skeletal myogenesis (Tapscott 2005), mutants lacking the single MRF-related factor in Drosophila (Nautilus) or C. elegans (HLH-1/CeMyoD) are still able to specify and differentiate striated muscle (Chen et al 1992;Balagopalan et al 2001). In addition, MEF-2 is a critical factor for striated muscle differentiation in Drosophila (Lilly et al 1994), as it is in vertebrate tissue culture , but its loss in C. elegans has no known effect on bodywall muscle development (Dichoso et al 2000). Given that the myogenic transcription factors are evolutionarily conserved in sequence, and most have been shown to be functional in heterologous systems, the developmental differences in the roles for these factors has been puzzling.…”

“…First identified genetically in a screen for uncoordinated movement, we originally cloned the gene encoding UNC-120 and showed it was involved in bodywall muscle differentiation. Subsequent studies have also implicated UNC-120 in bodywall muscle development, although its myogenic role has yet to be directly tested (Dichoso et al 2000;Baugh et al 2005b). A second candidate bodywall myogenic factor is HND-1, the only C. elegans protein closely related to the vertebrate HAND family of bHLH factors.…”

Investigating the origins of triploblasty: `mesodermal' gene expression in a diploblastic animal, the sea anemoneNematostella vectensis(phylum, Cnidaria; class, Anthozoa)

“…However, in both vertebrates and Drosophila, mef2 can also be detected in non-muscle and non-mesodermal tissues (Black and Olson, 1998;Schulz et al, 1996). Surprisingly, despite a high degree of sequence conservation, the C. elegans mef2 gene is not essential for muscle development (Dichoso et al, 2000). In the hydrozoan jellyfish Podocoryne, mef2 expression is widespread and highly dynamic (Spring et al, 2002).…”

The myogenic potency of HLH-1 reveals wide-spread developmental plasticity in earlyC. elegansembryos

“…In C. elegans, the only E-related factor, E/DA, is not detected in striated muscle cells and HLH-1 appears to function as a homodimer to activate transcription (Krause et al, 1997). In addition, members of the Twist and MEF-2 transcription factor families, which play important roles in vertebrate mesoderm specification and muscle differentiation (reviewed by Black and Olson, 1998;Castanon and Baylies, 2002), play little or no apparent role in embryonic body wall muscle development in C. elegans Dichoso et al, 2000). The transcriptional cascade regulating myogenesis in C. elegans embryogenesis is clearly distinct from that operating in the vertebrates.…”