VegT protein primarily specifies cells to become:
VegT is a maternal T-box transcription factor whose mRNA is anchored to vegetal cortex during oogenesis via cytoskeletal localization signals. After cleavage, daughter cells inheriting VegT translate protein that directly binds promoters of endodermal regulators Sox17, Mix1, Bix, and GATA4-6, committing them to endoderm and activating endodermal gene program. Simultaneously VegT activates Nodal ligands to induce adjacent mesoderm non-autonomously. Embryos lacking VegT fail to form gut and express epidermal markers vegetally, demonstrating VegT instructs endodermal specification rather than mesodermal, ectodermal, or neural programs which require different regulators and signaling inputs.
Ref: NCBI Bookshelf, Developmental Biology, Chapter: VegT specifies endoderm and induces mesoderm via Nodal.