Practice question

Beta-catenin nuclear entry drives vegetal gene regulatory network including Pmar1, Wnt8, blimp1b required for endomesoderm specification. Blocking nuclear entry via overexpression of cadherin cytoplasmic tail that sequesters beta-catenin, or dominant-negative TCF that occupies promoters without activation, or overactive GSK-three, eliminates endoderm and mesenchyme specification completely. Resulting embryos lack archenteron and skeleton, becoming permanent blastulae covered with long cilia called ciliated ectodermal balls, expressing only animal ectoderm markers like spec1. This animalized phenotype shows beta-catenin necessity for vegetal fates, producing ectodermal ball when blocked, opposite of vegetalization induced by GSK-three inhibition.