The human dopamine transporter (DAT1) gene contains a variable number of tandem repeats (VNTR) in its 3'-untranslated region (UTR). The linkage and association between the VNTR polymorphism of DAT1 and various neuropsychiatric disorders have been reported. We have determined the genomic structure of DAT1 genes containing 7-, 9-, 10-, and 11-repeat alleles and examined the effect of VNTR polymorphism in the 3'-UTR region of DAT1 on gene expression using the luciferase reporter system in COS-7 cells. Luciferase expression was significantly higher when the 3'-UTR of the DAT1 gene contained the 10-repeat allele than when it contained the 7- or 9-repeat alleles. This suggests that VNTR polymorphism affects the expression of the dopamine transporter.
The nervous system plays a critical role in adaptation to a new environment. In Caenorhabditis elegans, reduced access to food requires both changes in behavior as well as metabolic adaptation for survival, which is postulated to involve the bioamine octopamine. The transcription factor cAMP response element-binding protein (CREB) is generally activated by G-protein-coupled receptors (GPCRs) that activate G␣ s and is known to play an important role in long-term changes, including synaptic plasticity. We show that, in C. elegans, the CREB ortholog CRH-1 (CREB homolog family member 1) activates in vivo a cAMP response element-green fluorescent protein fusion reporter in a subset of neurons during starvation. This starvation response is mediated by octopamine via the GPCR SER-3 (serotonin/ octopamine receptor family member 3) and is fully dependent on the subsequent activation of the G␣q ortholog EGL-30 (egg-laying defective family member 30). The signaling cascade is only partially dependent on the phospholipase C (EGL-8) and is negatively regulated by G␣ o [GOA-1 (G-protein, O, ␣ subunit family member 1)] and calcium/calmodulin-dependent kinase [UNC-43 (uncoordinated family member 43)]. Nonstarved animals in a liquid environment mediate a similar response that is octopamine independent. The results show that the endogenous octopamine system in C. elegans is activated by starvation and that different environmental stimuli can activate CREB through G␣ q .Key words: aminergic; C. elegans; CREB; GPCR; G q ; octopamine; starvation Introduction cAMP response element-binding protein (CREB) is a signalactivated transcription factor that, after phosphorylation, induces expression of genes from promoters containing the cAMPresponse element (CRE) enhancer (Mayr and Montminy, 2001). CREB is activated by various physiological stimuli and plays important roles in many biological processes (Lonze and Ginty, 2002;Johannessen et al., 2004). The bioamine neurotransmitters dopamine, serotonin, and norepinephrine can activate CREB (Hyman, 1996;Mayford and Kandel, 1999;Simonneaux and Ribelayga, 2003). Most studies show that bioamine-induced CREB activation is dependent on G␣ s -coupled bioamine receptors through an adenylyl cyclase-protein kinase A (PKA) signaling pathway. However, little is known about in vivo mechanisms and the possible involvement of alternative cascades leading to CREB activation. Some in vitro studies suggest that G␣ q can activate CREB (Lin et al., 1998;Chalecka-Franaszek et al., 1999;Thonberg et al., 2002), although it is unknown whether the G␣ q -CREB pathway is of physiological relevance.Caenorhabditis elegans is a model organism that is particularly suitable for genetic studies. The bioamines dopamine (Sulston et al., 1975), serotonin (Horvitz et al., 1982), tyramine (Alkema et al., 2005), and octopamine (Horvitz et al., 1982) have been found in C. elegans and are believed to function as both neurotransmitters as well as neurohumoral factors. Octopamine is considered to be the invertebrate biological equiv...
The neurotransmitter dopamine plays an important role in the regulation of behavior in both vertebrates and invertebrates. In mammals, dopamine binds and activates two classes of dopamine receptors, D1-like and D2-like receptors. However, D2-like dopamine receptors in Caenorhabditis elegans have not yet been characterized. We have cloned a cDNA encoding a putative C. elegans D2-like dopamine receptor. The deduced amino acid sequence of the cloned cDNA shows higher sequence similarities to vertebrate D2-like dopamine receptors than to D1-like receptors. Two splice variants that differ in the length of their predicted third intracellular loops were identified. The receptor heterologously expressed in cultured cells showed high affinity binding to [ 125 I]iodo-lysergic acid diethylamide. Dopamine showed the highest affinity for this receptor among several amine neurotransmitters tested. Activation of the heterologously expressed receptor led to the inhibition of cyclic AMP production, confirming that this receptor has the functional property of a D2-like receptor. We have also analyzed the expression pattern of this receptor and found that the receptor is expressed in several neurons including all the dopaminergic neurons in C. elegans.
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