Distribution of MT₁ Melatonin Receptor Promoter-Driven RFP Expression in the Brains of BAC C3H/HeN Transgenic Mice

Abstract

The pineal hormone melatonin activates two G-protein coupled receptors (MT1 and MT2) to regulate in part biological functions. The MT1 and MT2 melatonin receptors are heterogeneously distributed in the mammalian brain including humans. In the mouse, only a few reports have assessed the expression of the MT1 melatonin receptor expression using 2-iodomelatonin binding, in situ hybridization and/or polymerase chain reaction (PCR). Here, we described a transgenic mouse in which red fluorescence protein (RFP) is expressed under the control of the endogenous MT1 promoter, by inserting RFP cDNA at the start codon of MTNR1a gene within a bacterial artificial chromosome (BAC) and expressing this construct as a transgene. The expression of RFP in the brain of this mouse was examined either directly under a fluorescent microscope or immunohistochemically using an antibody against RFP (RFP-MT1). RFP-MT1 expression was observed in many brain regions including the subcommissural organ, parts of the ependyma lining the lateral and third ventricles, the aqueduct, the hippocampus, the cerebellum, the pars tuberalis, the habenula and the habenula commissure. This RFP-MT1 transgenic model provides a unique tool for studying the distribution of the MT1 receptor in the brain of mice, its cell-specific expression and its function in vivo.

MT1 and MT2 Melatonin Receptors: A Therapeutic Perspective

“…The MT 1 and MT 2 receptor sites have been localized to discrete areas of the rodent and human nervous system—including the SCN, cerebellum, thalamus, hippocampus, as well as peripheral tissues—using receptor autoradiography with 2-[ 125 I]-iodomelatonin, in situ mRNA hybridization techniques, and immunohistochemistry (10–13). MT 1 and MT 2 receptor function has been established using mice with genetic deletion of either the MT 1 or MT 2 melatonin receptor (9, 14) or pharmacological approaches through the use of prototype competitive melatonin receptor antagonists such as luzindole and 4-phenyl-2-propionamidotetralin (4P-PDOT) (15, 16).…”

MT1 and MT2 melatonin receptors are expressed in nonoverlapping neuronal populations

“…Transgenic mice expressing marker enzymes under control of the endogenous MT1 or MT2 gene promoters should allow precise phenotyping of the cells containing MLT receptors. Previous attempts using bacterial artificial chromosome transgenesis did not provide convincing data . We have thus used a specific reporter “knock‐in” strategy replacing the MT1 or MT2 coding sequence with the LacZ reporter enzyme in the endogenous loci without modifying the endogenous upstream and downstream regulatory elements.…”

Genetic deletion of MT1 melatonin receptors alters spontaneous behavioral rhythms in male and female C57BL/6 mice

“…Deletion of MT 1 receptors in C57 mice also increased immobility on the forced swim test and impaired pre-pulse inhibition in the acoustic startle/pre-pulse inhibition test (Weil et al, 2006). The heterogeneous distribution of MT 1 receptors in the brain (Adamah-Biassi et al, 2014; Siuciak et al, 1990; Weaver et al, 1989) further suggests that this receptor subtype modulates complex behaviors. However, the role of endogenous melatonin and MT 1 receptors in the regulation of daily spontaneous behaviors remains largely uncharacterized.…”