Mas1相關基因家族為一G蛋白偶合受體家族，目前發現能專一表現於哺乳類痛覺相關感覺神經元。Mas1相關基因家族受體能被一些特定的內生性氨基化合物神經胜肽活化，例如：神經胜肽FF能活化小鼠的Mas1相關基因受體A1及C11、神經胜肽AF能活化小鼠的Mas1相關基因受體A4、γ2-促黑激素能活化大鼠的Mas1相關基因受體C、以及牛腎上腺髓肽22能活化人類的Mas1相關基因受體X1，而且不同胜肽對於不同家族受體之間的活化程度存在著相異性。一些Mas1相關基因受體在活化後能抑制特定調控痛覺的陽離子通道，如：鉀離子、鈉離子、或鈣離子通道。不過，Mas1相關基因B亞家族是否表現於痛覺感覺神經元，以及受體是否受專一的氨基化合物胜肽活化，均尚未了解。因此，此篇論文的目標在於偵測Mas1相關基因B亞家族其組織表現性及確認可能活化物。在反轉錄-聚合酵素連鎖反應後發現只有Mas1相關基因B4及B5能表現在背根神經節，但所偵測的Mas1相關基因B亞家族均表現於三叉神經節。另外感到有趣的地方，Mas1相關基因B4轉錄作用在酸敏感受體3剔除小鼠有顯著地變化，而經由原位雜合反應確定這些結果。這些結果暗示著Mas1相關基因B4的功能在與小鼠酸敏感受體3所引起的痛覺敏感有關。使用氨基化合物胜肽刺激於表現Mas1相關基因B4受體的人類腎臟胚胎細胞上，Mas1相關基因B4受體在被γ2-促黑激素活化後，利用Gi蛋白傳遞胞內訊息。然而，γ2-促黑激素必須使用過量的濃度才能活化Mas1相關基因B4受體，因此，並未確定出Mas1相關基因B4受體之專一活化物。 The subfamily B of Mas1-related gene (MrgBs) belongs to a family of G-protein coupled receptors (GPCRs) that are recently identified in mammals and specifically expressed in primary nociceptive (pain-related) sensory neurons. Reflecting the diversity and specificity of stimuli they respond, Mrgs are activated by different peptides containing RFamide motif, such as NPFF for mouse MrgA1 and C11, NPAF for mouse MrgA4, γ2-MSH for rat MrgC/SNSR1, and BAM22 for human MrgX1/SNSR3 and SNSR4. Activations of some Mrg receptors can inhibit the specific potassium and calcium channels that modulate nociception. However, whether MrgBs are involved in nociception and whether they are actived by RFamide peptides remain unknown. Therefore, the aim of this thesis is to examine tissue distribution of MrgB genes and identify their ligands. In all of MrgB members tested, only MrgB4 and B5 transcripts were expressed in dorsal root ganglion (DRG), but all MrgB genes were expressed in trigeminal ganglion (TG). Interestingly, MrgB4 transcripts were significantly changed in acid-sensing ion channel 3 (ASIC3) deficient mice and such results were confirmed using in situ hybridization. These results suggest that MrgB4 may have functions related to the enhanced sensitivity of ASIC3+/+ mice to painful stimuli. Using RFamide pepides to test MrgB4-overexpressing HEK293 cells, MrgB4 was activated by γ2-MSH through the Gi pathway. Nevertheless, the concentration of γ2-MSH for MrgB activation was too high, the specific ligands for MrgB4, therefore, are inconclusive.
