Transition Elements: Elements with partially filled d orbitals. They constitute groups 3-12 of the periodic table of elements.DNA Transposable Elements: Discrete segments of DNA which can excise and reintegrate to another site in the genome. Most are inactive, i.e., have not been found to exist outside the integrated state. DNA transposable elements include bacterial IS (insertion sequence) elements, Tn elements, the maize controlling elements Ac and Ds, Drosophila P, gypsy, and pogo elements, the human Tigger elements and the Tc and mariner elements which are found throughout the animal kingdom.Response Elements: Nucleotide sequences, usually upstream, which are recognized by specific regulatory transcription factors, thereby causing gene response to various regulatory agents. These elements may be found in both promoter and enhancer regions.Enhancer Elements, Genetic: Cis-acting DNA sequences which can increase transcription of genes. Enhancers can usually function in either orientation and at various distances from a promoter.Epithelial-Mesenchymal Transition: Phenotypic changes of EPITHELIAL CELLS to MESENCHYME type, which increase cell mobility critical in many developmental processes such as NEURAL TUBE development. NEOPLASM METASTASIS and DISEASE PROGRESSION may also induce this transition.