Assessment of the presence of chemosensing receptors based on bitter and fat taste in the gastrointestinal tract of young pig

Knowledge on porcine bitter and fat taste receptors and on their expression in gastrointestinal tract of pigs is scarce. We searched for the presence of porcine homologous sequences for 13 human transcripts of bitter and fat taste receptors, in ENSEMBL and NCBI databases. For taste 2 receptor (TAS2R) 8, alignment was not observed; for TAS2R13 and TAS2R46 the porcine predicted sequence aligned with several other human bitter genes. For 7 genes for bitter taste (TAS2R1, TAS2R3, TAS2R7, TAS2R9, TAS2R10, TAS2R16, TAS2R38) and for 3 genes for fat taste (GPR40, GPR43, GPR120), a full homology for exons sequences was found and primers were designed by PRIMER3. These 7 genes were amplified with real-time PCR and verified on agarose gel, in 5 gastro-intestinal segments of weaned pigs: oxyntic (ST1), pyloric (ST2) and cardiac to oxyntic transition mucosa (ST3); jejunum (JEJ) and colon (COL). Suitability of mRNA was verified by amplifying RPL4 and HMBS2 genes. Each bitter taste gene was detectable on agarose gel in at least one subject of all the gastro-intestinal segment except for TAS2R3 and TAS2R38 that were never detected in ST1 and COL, respectively. The inspection of bitter taste genes amplification curve indicated that the expression was in general very low. GPR43 and GPR120 were present in all segments from all pigs. Expression was not detected for GPR40. Data also indicate that colon is the preeminent tract where fat detection by GPR120 takes place (P < 0.001). The presence of gene expression for several chemosensing receptors for bitter and fat taste in different compartments of the stomach confirms that this organ should be considered a player for the early detection of bolus composition.