NKX2-3 is a member of the NKX family of homeodomain-containing transcription factors, which are implicated in many aspects of cell type specification and maintenance of differentiated tissue functions.Nkx2.3 contains a homeobox, a conserved NK2 domain, a C-terminal GIRAW motif typical of NKX2 proteins, and an N-terminal homology domain conserved among NK2 genes. RT-PCR and whole-mount in situ hybridization analyses detected Nkx2.3 expression primarily in gut mesoderm, distinct regions of the branchial arches, the tongue epithelium, and limited domains in the developing jaws, possibly including tooth anlagen.Nkx2.3 deficiency resulted in severe morphologic alterations in gut and spleen with early postnatal lethality in the majority of homozygous mutants.