Lrmp/Jaw1 is expressed in sweet, bitter, and umami receptor-expressing cells

Abstract

Inositol 1,4,5-triphosphate-mediated calcium (IP3-Ca2+) signal cascade is an essential process in sweet, bitter, and umami taste signal transduction. Although the main components of this cascade have been identified, the candidate regulators of them in taste tissues are still unclear. In an effort to identify genes involved in taste signal transduction, we found that a gene encoding lymphoid-restricted membrane protein (Lrmp/Jaw1) was expressed in mouse taste tissues. Here we report that Lrmp/Jaw1 is specifically expressed in sweet, bitter, and umami taste receptor-expressing cells of mouse circumvallate, foliate, and fungiform papillae. In addition to this specific expression patterns, we found that Lrmp/Jaw1 is associated with type III IP3 receptor (IP3R3) via its coiled-coil domain in the COS7 heterologous expression system. These results raise the possibility that Lrmp/Jaw1 interacts with IP3R3 in taste cells and suggest an important role for Lrmp/Jaw1 in the IP3-Ca2+ signal cascade in sweet, bitter, and umami taste signal transduction.

Figure 1

Cellular distribution for mRNA of Lrmp/Jaw1 gene in taste buds. Mouse CV, FL, and FF papillae slices (5 μm) were used for in situ hybridization. The broken lines indicate the outline of each taste bud. The expressions of the genes were visualized by NBT–BCIP. The scale bars indicate 50 μm.

Figure 2

Coexpression patterns of Lrmp/Jaw1 and known taste-related genes. (a) Comparison of the mRNA expression pattern of Lrmp/Jaw1 (green) with Trpm5 (red, upper) and Mash1 (red, lower) in CV papillae by double-colored in situ hybridization. (b) Comparison of the mRNA expression pattern of Lrmp/Jaw1 (green) with Trpm5 (red) in FF papillae by double-colored in situ hybridization. After merging, colocalization is indicated in yellow. The coexpression ratios in CV papillae are summarized in Table 1. The scale bars indicate 50 μm.

Figure 3

Coexpression patterns of Lrmp/Jaw1 and IP₃R3 in CV papillae. Comparison of the protein expression pattern of Lrmp/Jaw1 (red) and IP₃R3 (green) by double-colored immunohistochemistry. After merging, colocalization is indicated in yellow. The scale bars indicate 50 μm.

Figure 4

Association between Lrmp/Jaw1 and IP₃R3 in COS7 heterologous expression system. (a) Schematic diagrams of FLAG epitope–tagged Lrmp/Jaw1 constructs with/without a coiled-coil domain (FLAG-Lrmp/Jaw1 and FLAG-Lrmp/Jaw1Δ). TM, transmembrane domain, numbers indicate each amino acid residue. (b) Comparison of the subcellular localizations of IP₃R3 (green, upper panel; red, lower panel) and FLAG-Lrmp/Jaw1 (red, upper panel) or FLAG-Lrmp/Jaw1Δ (green, lower panel) by double-colored immunocytochemistry. After merging, colocalization is indicated in yellow. The scale bars indicate 10 μm. (c) Co-immunoprecipitated proteins with anti-FLAG antibody were detected by anti-IP₃R3 antibody (upper) or anti-FLAG antibody (lower). Arrows indicate the predicted molecular weight (65 kDa for FLAG-Lrmp/Jaw1, 50 kDa for FLAG-Lrmp/Jaw1Δ). The genes transfected in COS7 is indicated by symbols (+ or −).