Neurotrophin-4 (NT-4) is a member of the neurotrophin family of growth factors. To study the molecular mechanisms that govern NT-4 expression, we have cloned and characterized the rat genome region encoding NT-4. The rat NT-4 gene consists of three exons: two 5'-flanking noncoding exons and a coding exon. NT-4 mRNA transcription is controlled by two promoters flanking the noncoding exons. Alternative splicing of the second intron results in a NT-4 mRNA with a different open reading frame, encoding a shorter protein lacking pre-NT-4 sequence. A rat NT-4 gene fragment, containing all exons and introns in addition to 1.4 kb of the upstream genomic sequence, has been introduced into mice. This transgene enables partial recapitulation of the expression pattern of NT-4 mRNA and confers activity-dependent expression of the NT-4 mRNA in muscle.