Expression profile of addicsin/GTRAP3-18 mRNA in mouse brain

Addicsin is a murine homologue of rat glutamate-transporter-associated protein 3-18 (GTRAP3-18), a putative modulator of neural glutamate-transporter excitatory amino acid carrier 1 (EAAC1). The other molecular functions of addicsin, however, remain largely unknown. We analyzed here the regional and cellular distribution of addicsin transcript in the mature brain using in situ hybridization analysis, and examined the sequential addicsin mRNA expression levels in the developing brain using Northern blot analysis. In the mature brain, we found addicsin mRNA to be ubiquitously expressed in neuron-like cells, but not glial cells, in various brain regions including the olfactory bulbs, hippocampus and cerebral cortex. In the hippocampus, addicsin mRNA was expressed in the neuron-like cells of the CA1-CA3 pyramidal cell layer and the interneuron-like cells of the stratum oriens, stratum radiatum and stratum lacunosum-moleculare. Addicsin transcripts were also extremely abundant in trigeminal neurons such as the principal trigeminal nucleus, mesencephalic trigeminal nucleus and motor trigeminal nucleus. Our evidence suggests that addicsin mRNA is chiefly expressed in the excitatory and inhibitory neurons, and that addicsin may participate in the functional expression of the somatic sensory system by modulation of EAAC1-mediated glutamate transport. Northern blot analysis revealed that addicsin mRNA levels increased with maturation, reaching their maximum level at postnatal day 5 (P5), then significantly declined by about 50% until P14, suggesting that addicsin may contribute to embryogenesis and synaptogenesis in the developing brain. Thus, addicsin may participate in multiple physiological functions in the developing and mature brain.