Brain-derived neurotrophic factor (BDNF) 1 is a member of neurotrophin family, structurally related to nerve growth factor, neurotrophin-3, and neurotrophin-4/5. Its biological activity is mediated by tyrosine kinase receptor B (TrkB) and its downstream signaling (1). The gene is highly expressed and widely distributed in the central nervous system, and it plays a significant role in the maintenance of function and survival of neurons (for review, see Ref.2). Evidence accumulated in recent years suggests that BDNF is also involved in the modulation of synaptic activity in the adult brain, producing long lasting changes in synaptic structure and function (for reviews, see Refs. 3-5).There is a growing interest in BDNF as a potential therapeutic agent for neurodegenerative diseases, because its deficiency was found in brains of both Alzheimer's and Parkinson's patients (6 -10). Indeed, BDNF treatment has been shown not only to potentiate synaptic transmission in vivo (11, 12) but also to increase neuronal survival and augment some behavioral changes in animal models (13,14). However, more recent data indicate that BDNF can also induce behavioral sensitization by causing an overexpression of dopamine D3 receptors and could, actually, contribute to the amplification of pathophysiologies associated with conditions such as epilepsy, drug addiction, schizophrenia, and Parkinson's disease (15, 16). Clearly, further work is required to resolve some of these potential side-effects. In contrast to a large body of work on the temporal and spatial patterns of BDNF expression in neurodevelopment and neurodegeneration, relatively little is known about the transcriptional regulation of the human BDNF gene. This is partially due to the fact that the genomic structure of the human gene has not yet been fully elucidated. The gene was first localized to chromosome11p13 and predicted to consist of multiple exons (17), but the existence of multiple transcripts, derived from different exons, was demonstrated only recently by Aoyama et al. (18) in human neuroblastoma cells. A more detailed transcript mapping of an 810-kb region of chromosome 11p13-14 further defined its genomic localization, although no additional information on the actual structure of the gene itself was presented (19).The existence of multiple human BDNF transcripts (18) is consistent with a genomic structure similar to that of the rat gene, which consists of four short 5Ј exons, each controlled by a distinct promoter, and one 3Ј exon encoding the mature BDNF protein (20,21). In the rat, the four promoters direct expression of the BDNF gene in a tissue-specific manner, i.e. promoters I and II are active preferentially in neurons, whereas promoters III and IV are active both in neurons and in a limited number of non-neuronal tissues such as lung and heart (20, 21). Thus far, only a limited characterization of a 3.2-kb genomic fragment of the human gene containing some structural elements of a promoter was reported (22).Recently, two transcription factors, CREB and ...
