Clathrin light chain B (LCB) is a major component of clathrin coated vesicles, which are structures involved in intracellular transport. A neuron-specific isoform of LCB is generated by incorporation of a single exon (EN) using an alternative splicing mechanism that reflects the special demands of neurons, such as axonal transport and synaptic neurotransmission. Here, we demonstrate that this 1 neuron-specific exon is developmentally regulated and is excluded in non-neuronal cells because its 5' and 3' splice sites deviate from the mammalian consensus sequences. A gel retardation assay indicated the presence of a developmentally regulated factor in brain that binds to the neuronal exon. In addition, EN usage is repressed by increasing the concentration of htra2-betal, a splice factor whose isoform expression is influenced by neuronal activity. We propose that a brain-specific factor is involved in EN recognition during development and adulthood. In addition, ubiquitously expressed splicing factors such as htra2-betal are involved in regulating EN expression in the adult brain. (C) 1999 Elsevier Science B.V. All rights reserved.