Brain-derived neurotrophic factor gene expression in the developing zebrafish.

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family of polypeptides that includes NGF, NT-3, NT-4/5 and NT-6. Although neurotrophins are known to be expressed in teleost fishes little is known about their functions in the development of these vertebrates. We are therefore studying BDNF in the zebrafish, Danio rerio. The structure of zebrafish BDNF mRNA was established using PCR and cDNA cloning. The encoded BDNF was 91% identical to mammalian BDNF. Southern blot analysis revealed a unique BDNF gene. Northern blot analysis detected two heterogeneous populations of BDNF transcripts centered at 1.6 and 2 kb. BDNF transcripts were first measurable 24 h post-fertilization (pf). Their abundance relative to total transcripts increased 6-fold between 1 day and 3 days pf and again 2-fold by 7 days pf. In situ hybridization analyses of 4-day-old larvae revealed BDNF transcripts in the retina, brain, otic vesicle, pectoral fin and the hair cells of the neuromast. The early onset and cellular sites of expression suggest that BDNF functions in nervous system and fin development in the zebrafish.