The selector genes midline and H15 control ventral leg pattern by both inhibiting Dpp signaling and specifying ventral fate

• Published in: Developmental biology Vol. 455; no. 1; pp. 19 - 31
• Main Authors: Svendsen, Pia C., Phillips, Lindsay A., Deshwar, Ashish R., Ryu, Jae-Ryeon, Najand, Nima, Brook, William J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2019
• Subjects: Animals; Animals, Genetically Modified; Body Patterning - genetics; Drosophila melanogaster - genetics; Drosophila melanogaster - growth & development; Drosophila melanogaster - metabolism; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Extremities - growth & development; Gene Expression Regulation, Developmental; Imaginal Discs - growth & development; Imaginal Discs - metabolism; Mutation; Signal Transduction - genetics; T-Box Domain Proteins - genetics; T-Box Domain Proteins - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2019.05.012

mid and H15 encode Tbx20 transcription factors that specify ventral pattern in the Drosophila leg. We find that there are at least two pathways for mid and H15 specification of ventral fate. In the first pathway, mid and H15 negatively regulate Dpp, the dorsal signal in leg development. mid and H15 block the dorsalizing effects of Dpp signaling in the ventral leg. In loss- and gain-of-function experiments in imaginal discs, we show that mid and H15 block the accumulation of phospho-Mad, the activated form of the Drosophila pSmad1/5 homolog. In a second pathway, we find mid and H15 must also directly promote ventral fate because simultaneously blocking Dpp signaling in mid H15 mutants does not rescue the ventral to dorsal transformation in most ventral leg structures. We show that mid and H15 act as transcriptional repressors in ventral leg development. The two genes repress the Dpp target gene Dad, the laterally expressed gene Upd, and the mid VLE enhancer. This repression depends on the eh1 domain, a binding site for the Groucho co-repressor, and is likely direct because Mid localizes to target gene enhancers in PCR-ChIP assays. A mid allele mutant for the repressing domain (eh1), mideh1, was found to be compromised in gain-of-function assays and in rescue of mid H15 loss-of-function. We propose that mid and H15 specify ventral fate through inhibition of Dpp signaling and through coordinating the repression of genes in the ventral leg. •Midline blocks Dpp signaling downstream of the Dpp receptor.•Mid decreases pMad levels.•Mid also specifies fate independently of Dpp-inhibition.•Mid represses ventral and lateral target genes with the eh1 domain.•Mid requires the eh1 domain to specify ventral fate in the leg.