The Flt-3 (fms-like tyrosine kinase) receptor, also named Flk-2 (fetal liver kinase) and STK-1(stem cell tyrosine kinase) is a member of the class III subfamily of receptor tyrosine kinases that also includes c-kit, the receptor for SCF, and fms, the receptor for M-CSF. Mouse Flt-3 shares 85% amino acid sequence identity with human Flt-3. Flt-3 expression has been detected in various tissues, including placenta, gonads, and tissues of nervous and hematopoietic origin.