Final answer:
Cell differentiation, essential for embryo development, is regulated by location-specific chemical signals from the embryonic environment that control gene expression. Transcription factor proteins play a key role in determining which genes are expressed. Cells specialize into different types through these mechanisms.
Step-by-step explanation:
Cell differentiation, which is essential for the development of embryos, is most directly regulated by location-specific chemical signals from the cell's embryonic environment. These signals set in motion a cascade of events that regulate gene expression. The process of differentiation is controlled by the action of transcription factor proteins, which bind to DNA and promote or hinder the transcription of specific genes. Through these mechanisms, cells specialize into different types in the human body.