Practice question

VegT is essential vegetally for endoderm and mesoderm formation. Embryos depleted of maternal VegT mRNA by antisense oligonucleotides lose activation of Sox17 and Nodal genes Xnr1-4, so vegetal blastomeres fail to become endoderm or induce mesoderm at marginal zone. Without TGF-beta signals, entire marginal zone and vegetal region adopt default ectodermal fate expressing epidermal keratin and ciliated cell markers. Result is animalized blastula consisting solely of ciliated epidermis without gut or mesoderm, proving VegT's non-redundant role in germ-layer specification and embryonic patterning for vertebrate development.