Micromere specification involves:
Specification of micromeres depends on intricate gene regulatory network based on activation of Pmar1 by nuclear beta-catenin localized vegetally. Pmar1 encodes transcriptional repressor that specifically inhibits transcription of HesC, itself a global repressor of micromere fate genes. This double-negative gate Pmar1 represses HesC, HesC represses Delta, alx1, ets1, tbr, tel, dri, allows micromere program expression exclusively where Pmar1 present in large micromeres. Therefore micromere specification fundamentally involves Pmar1 and HesC interaction forming logic gate. Beta-catenin and Delta act upstream and downstream respectively, but core gate is Pmar1-HesC, while Frizzled and Dishevelled regulate beta-catenin earlier.
Ref: Oliveri et al., Development 2008: Micromere specification via Pmar1-HesC double-negative gate regulatory.