Multiple elements may be used for regulation of the GAP-43 gene in different cell-types

Recent evidence suggests that GAP-43 expression is not restricted to the nervous system, but may also occur outside the neural cell lineage. Two distinct patterns of GAP-43 regulation can therefore be distinguished. The first is the regulation of GAP-43 expression in multiple cell-types, and the second is the gene's temporal modulation within one specific cell-type. The latter type is well documented for neurons, where GAP-43 regulation is regulated in a fashion that is dependent on axon integrity. Results from partial analysis of the GAP-43 promoter/enhancer region indicate that at least some of these aspects of GAP-43 gene regulation may be accounted for by distinct cis-acting elements. For example, the expression of a rat GAP-43 promoter fusion gene in epidermal cells of transgenic zebrafish is dependent on an enhancer element, that is clearly distinct from the minimal neural-specific promoter. Characterization of specific GAP-43 regulatory elements responsible for particular aspects of its regulation may provide insight to signal pathways also utilized by other genes during development. Ultimately, a better understanding of the molecular events during development could help to define more precisely the complex sequences necessary for the establishment of an intact organism.