Practice question

VegT is maternally encoded T-box transcription factor localized vegetally, essential for initiating Nodal transcription Xnr1,2,4,5,6 and endoderm specification via Sox17 and Mix. Antisense oligonucleotide depletion of VegT abolishes endoderm and mesoderm gene activation because Nodal signals absent, leaving animal hemisphere under unopposed BMP. Caps become entirely epidermal keratin and ciliated cells with expanded epidermis markers, producing embryo lacking gut, muscle, notochord and blood, purely epidermal ball. Rescue requires Xenopus Nodal mRNA injection demonstrating VegT master regulator of mesendoderm and epidermal repression.