The C. elegans Twist target gene, arg-1, is regulated by distinct E box promoter elements

Area of Science:

• Developmental Biology
• Molecular Genetics
• Gene Regulation

Background:

• Proper metazoan mesoderm development relies on the basic helix-loop-helix (bHLH) transcription factor, Twist.
• Twist-containing dimers bind to E box promoter elements (CANNTG) to regulate target gene expression.
• In *Caenorhabditis elegans*, CeTwist is essential for a subset of mesodermal cells.

Purpose of the Study:

• To investigate how CeTwist controls the expression of its target gene, arg-1.
• To elucidate the specific roles of E box elements within the arg-1 promoter in CeTwist-mediated gene regulation.
• To explore potential involvement of other transcription factors in arg-1 expression.

Main Methods:

• Analysis of a 385bp arg-1 promoter region containing three E box elements.
• Assessing the sufficiency of this promoter region for CeTwist-dependent expression.
• Investigating differential regulation of arg-1 expression across tissues.
• In vitro binding assays to determine CeTwist dimer affinity for different E boxes.

Main Results:

• A 385bp arg-1 promoter region with three E boxes is sufficient for full CeTwist-dependent expression.
• Each of the three E boxes (E1, E2, E3) plays a unique regulatory role in distinct mesodermal tissues.
• E2 is essential for expression in the full set of tissues and binds CeTwist dimers with higher affinity than E1 or E3.
• A novel regulatory site, not bound by CeTwist in vitro, is required for arg-1 expression in a subset of tissues.

Conclusions:

• CeTwist-dependent arg-1 expression is finely tuned by the distinct functions of multiple E box elements.
• Tissue-specific regulation of arg-1 involves differential utilization of E boxes and potentially other transcription factors.
• A model is proposed where CeTwist gene regulation depends on tissue-specific binding to distinct sets of E boxes.