The Rab3A locus: Studies of neuronal expression and effects on behavior

RAB3A (Ras-related GTP-binding protein 3A) and its interacting proteins play central roles in neurotransmitter release and synaptic plasticity. However, the mechanism underlying the neuronal expression of these genes remains largely unknown. Furthermore, in vivo function of RAB3A on neurobehaviors is still under investigation.;Using unbiased in vivo and in vitro screens, we characterized the cis elements regulating the Rab3A gene. A set of identified regulatory elements of the Rab3A gene corresponded to the defined Rab3A multi-species conserved elements (MCE). Thus, we analyzed intergenic MCEs in the vicinity of nine presynaptic genes including Rab3A, which are highly and specifically expressed in brain regions, and identified 16 transcription factor binding sites (TFBSs) enriched in these MCEs. Based on a combined occurrence of the 16 TFBSs, MCEs in the vicinity of 107 presynaptic genes were scored and ranked. We experimentally validated the scoring strategy by showing that 12 of 16 of (75%) high-scoring MCEs functioned as neuronal enhancers in a cell-based assay. Therefore, this work reveals a regulatory network controlling neuronal-specific expression of genes localized in the presynaptic terminal of neurons.;Previous studies revealed that both heterozygotes and homozygotes of Rab3A mouse mutants, including a null allele and an ENU-induced mutant (Earlybird), exhibited several behavioral anomalies in learning and memory, circadian, and homeostatic response to sleep loss (Kapfhamer et al. 2002; Yang et al. 2006). To further address the dosage effect of RAB3A on behavior, we generated transgenic mice with additional copies of the Rab3A gene. The transgenic mice showed a 2-fold increase in RAB3A protein level. In a cross between Rab3A-null and transgenic mice, transgenic Rab3A completely restored RAB3A level and rescued behavioral deficiency (short circadian period) in Rab3A-null mutants. Behavioral assessment of Rab3A transgenic mice revealed a mild defect in motor coordination, decreased exploratory activity, increased anxiety-like behavior, and enhanced associative learning and memory. In a cross between Earlybird and Rab3A transgenic mutants, Earlybird homozygotes in the presence of a transgene (Rab3AEbd/Ebd, Rab3ATg/+) failed to survive. This study describes an additional mutant allele of Rab3A in the mouse and further reveals a dose-dependent role for a gene involved in neurotransmitter release.