ID2 also known as GIG8 is a member of the basic helix-loop-helix (bHLH) family. ID2 plays a crucial role in regulating cell differentiation and proliferation by inhibiting DNA binding activity of other bHLH proteins. Such inhibition is particularly important in muscle development, as ID2 prevents binding of myogenic factors such as E12 and Myo D, thereby suppressing muscle-specific gene expression. As muscle cells differentiate, ID protein levels decrease, allowing E12 and/or E47 to form heterodimers with Myo D and myogenin, which are essential for activating myogenic differentiation. Expression of ID proteins, including ID2, is tightly regulated by growth factors, and studies have shown that reducing Id mRNA levels can delay reentry of quiescent cells into cell cycle following growth factor stimulation.