Practice question

Double-negative gate explains restricted skeletogenic gene regulatory network to large micromeres of sea urchin embryo. Maternal nuclear β-catenin activates transcription factor Pmar1 specifically in micromeres shortly after their birth. Pmar1 protein is a potent repressor that represses transcription of another global repressor, HesC, which is expressed ubiquitously otherwise. HesC normally represses many micromere fate genes including Alx1, Ets1, Tbr, Tel and signaling ligand Delta. By repressing HesC, Pmar1 derepresses those genes allowing skeletogenic differentiation only where Pmar1 present. This Pmar1-HesC tandem repression circuit exemplifies double-negative logic in developmental gene regulatory networks.