The T-box gene optomotor-blind organizes proximodistal leg patterning in the beetle Tribolium castaneum by repressing dorsal Dpp pathway activity

midline represses Dpp signaling and target gene expression in Drosophila ventral leg development

Ventral leg patterning in Drosophila is controlled by the expression of the redundant T-box Transcription factors midline (mid) and H15. Here, we show that mid represses the Dpp-activated gene Daughters against decapentaplegic (Dad) through a consensus T-box binding element (TBE) site in the minimal enhancer, Dad13. Mutating the Dad13 DNA sequence results in an increased and broadening of Dad expression. We also demonstrate that the engrailed-homology-1 domain of Mid is critical for regulating the levels of phospho-Mad, a transducer of Dpp-signaling. However, we find that mid does not affect all Dpp-target genes as we demonstrate that brinker (brk) expression is unresponsive to mid. This study further illuminates the interplay between mechanisms involved in determination of cellular fate and the varied roles of mid.

Summary: Ventral patterning is controlled in part by the T-box Transcription factor midline blocking Dpp signaling and Dpp-activated genes, though midline does not affect the Dpp-repressed gene brk.