Transcriptional regulator essential for normal development and functions of the small intestine and spleen. Activates directly MADCAM1 expression. Required for homing of lymphocytes in spleen and mucosa-associated lymphoid tissue. May have a role during pharyngeal organogenesis. Expressed in spleen and intestine. Also expressed in salivary gland and tongue. Expressed in gut mesenchyme during pre- and postnatal development. Expressed as well in the pharyngeal floor and pouches, and in the oral and branchial arch ectoderm. Expression persisted in the developing thyroid until birth, in mucous forming cells of salivary glands and in odontogenic epithelium of the mandible. Belongs to the NK-2 homeobox family.