FOXN1,also named as Forkhead box protein N1,is a 648 amino acid protein,which contains 1 fork-head DNA-binding domain and localizes in the nucleus. FOXN1 as transcriptional regulator regulates the development,differentiation,and function of thymic epithelial cells (TECs) both in the prenatal and postnatal thymus. FOXN1 acts as a master regulator of the TECs lineage development and is required from the onset of differentiation in progenitor TECs in the developing fetus to the final differentiation steps through which TECs mature to acquire their full functionality.