NKX2-1, also known as thyroid transcription factor 1 (TTF-1) is a transcription factor that regulates gene expression by binding to specific DNA sequences. A member of the NKX family of homeodomain-containing proteins, it plays a key role in the development and function of the thyroid, lung, and brain. In the thyroid, NKX2-1 is expressed during embryonic development and is essential for the formation and differentiation of thyroid follicular cells.