The adrenergic β2 receptor (β2-AR) gene is embedded (nested) within the serotonin 5-HT4 receptor (5-HT4-R) gene and these two receptors can interact at the transcriptional and post-transcriptional levels. The mouse 5-HT4-R gene contains a number of exons and codes at least four mRNA splice variants (5-HT4(a)-R, 5-HT4(b)-R, 5-HT4(e)-R, 5-HT4(f)-R), whereas the β2-AR gene is intronless. Since 5-HT4-Rs and β2-ARs can form homodimers and heterodimers and they increase intracellular cAMP levels, these receptors may be important for integrating serotonergic and noradrenergic signals at the single-neuron level. Both 5-HT4-R and β2-AR have been implicated in autism spectrum disorders, depression, and Alzheimer’s disease. In the fetal brain, these receptors may mediate the effects of stress on neurodevelopmental processes. We used quantitative reverse-transcription PCR (qRT-PCR) to investigate the developmental expression of 5-HT4-R and β2-AR in the mouse telencephalon at embryonic days (E) 13–18. At E13–E14, the mRNA levels of all 5-HT4-R splice variants were very low, but by E17–E18 they increased 7-fold (5- HT4(a)-R), 5-fold (5-HT4(b)-R), 9-fold (5-HT4(e)-R), and 11-fold (5-HT4(f)-R). The expression of 5-HT4(a)-R and 5-HT4(b)-R was rapidly upregulated between E14 and E15, at the time when the thalamocortical projections arrive in the telencephalon. This pattern was not observed in the expression of 5-HT4(e)-R and 5-HT4(f)-R, the mRNA levels of which showed a steady, gradual increase from E13 to E18. The β2-AR mRNA levels were relatively high throughout the studied period of development and increased only by 70% from E13–E14 to E17–E18. These findings suggest that 5-HT4-R splice variants and β2-ARs are differentially regulated in the embryonic telencephalon and that their relative amounts may carry developmentally important information.

Keywords:
5-hydroxytryptamine, Autism spectrum disorders, Brain development, Cerebral cortex, Depression, Nested genes, Norepinephrine, Quantitative real-time RT-PCR, Stress
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© 2010 S. Karger AG, Basel
2010
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