May regulate cell proliferation in a tissue-specific manner. Expressed in the muscle layer of embryonic somites. In tailbud embryos, expressed throughout the entire myotome but at the mid-tailbud stage (stage 32), expression becomes restricted to the outer periphery of the somite so that by the tadpole stage only the outer, type I cells show expression. Also expressed in the dorsal cement gland and in the myocardial layer of the developing heart. In all tissues, expression begins after terminal differentiation. First detectable at low levels at the late gastrula/early neurula embryo (stage 14). Levels remain approximately constant throughout subsequent embryonic development, before declining in the tadpole. By ihh/bhh. Based on similarity to Drosophila 'bagpipe/bap', the name 'koza' was chosen after a Polish musical instrument related to the Scottish bagpipe. Belongs to the NK-3 homeobox family.