The genome of Chinese longsnout catfish provides novel insights into the feeding preference and corresponding metabolic strategy of carnivores

Figure 3. Tas1r3 is the determinant element in fish feeding preference.(B) Expression of tas1r3 in the intestinal (n = 6), brain (n = 4) and oropharyngeal (n = 8) tissues of grass carp before or after the feeding habit transition (FHT) from carnivory to herbivory. Grass carp before and after the FHT were sampled when they reached a body length of 2.82 ± 0.18 cm and 6.21 ± 0.63 cm at 46 and 116 days post hatching, respectively.  (E) Relative expression of tas1r3 in the oropharynx, brain, and intestinal tissues of the wild-type control or tas1r3-deficient zebrafish (n = 3). (J) Amount of duckweed consumed by wild-type control or tas1r3-deficient zebrafish in 12 h (n = 10). (K) Total food intake of soybean meal diet by wild-type control or tas1r3-deficient zebrafish (n = 3). (L) Feeding rate of soybean meal diet consumed by wild-type control or tas1r3-deficient zebrafish (calculated on a body weight basis per day) (n = 3). (N) Biting times of fishmeal and grassmeal blocks in control and tas1r3-deficient zebrafish (n = 8). *, P < 0.05. **, P < 0.01. ***, P < 0.001.Figure 4. miR-216b is responsible for regulating the expression of tas1r3.(A) Volcano map of intestine miRNAs expression levels in grass carp before or after the feeding habit transition (FHT) from carnivore to herbivore. (C) The expression analysis of microRNA expression in intestine of grass carp before and after the feeding habit transition (n = 10). (D) Relative Dual-Luciferase activity analysis was performed to detect the effects of microRNA on tas1r3 3’UTR activity (n = 3).Figure 5. Feeding preference affects metabolic traits in fish.(A) Relative expression of hepatic trypsin in wild-type control or tas1r3-deficient zebrafish (n = 8). (B) Relative expression of hepatic trypsin in grass carp before and after the feeding habit transition (FHT) from carnivores of chironomid larvae to herbivores of Hydrilla verticillate (n = 6). (C-G) Intestinal trypsin activity (n = 6), plasma TAA (n = 6), intestine α-AMS (n = 6), and hepatic GCK (n = 4) and PK activities (n = 4) of grass carp before and after the FHT from carnivory to herbivory. (H) Heat map of hepatic differentially expressed genes (DEGs) associated with amino acid and glucose metabolism in grass carp before or after the FHT from carnivory to herbivory. (I-J) qPCR validation of RNA-seq results for amino acid and glucose metabolism in grass carp before or after the FHT from carnivory to herbivory (n ≥ 4). (K) Relative expression of hepatic genes related to amino acid metabolism in wild-type control or tas1r3-deficient zebrafish (n ≥ 6). *, P < 0.05. **, P < 0.01. ***, P < 0.001.  Figure 6. The relationship between feeding preferences and corresponding metabolic strategies in fish with distinct feeding habits.(A-B) Intestinal trypsin activities and plasma TAA contents in two typical carnivorous fish, Chinese longsnout catfish (Leiocassis longirostris Günther) and largemouth bass (Micropterus salmoides), and two typical herbivorous fish, grass carp (Ctenopharyngodon idellus) and blunt snout bream (Megalobrama amblycephala) (n ≥ 7). Values marked with different superscripts above the bars indicate significant differences (P < 0.05). (C-F) Intestinal trypsin activities, plasma TAA contents, and got and gpt activities of the liver of Leiocassis longirostris and Ctenopharyngodon idellus fed a fishmeal or plantmeal diet, respectively (n = 6). (G-H) Relative expression of hepatic genes related with amino acid metabolism and glucose metabolism in grass carp (Ctenopharyngodon idellus) fed a fishmeal or plantmeal diet, respectively (n = 12). (I-J) Transcriptional level of hepatic genes related with amino acid and glucose metabolism in Leiocassis longirostris fed a fishmeal or plantmeal diet, respectively (n = 12). ns, P > 0.05. **, P < 0.01. ***, P < 0.001. ****, P < 0.0001.Supplemental Figure S6. Relative expression of tas1r1 and tas1r3 in oropharyngeal and intestinal tissues of juvenile and adult Chinese longsnout catfish (n ≥ 4). Supplemental Figure S7. Relative expression of genes related with feeding preference pathway in oropharyngeal and brain of grass carp before or after the feeding habit transition (FHT) from carnivore to herbivore (n ≥ 6).Supplemental Figure S8. Amount of artemia salina diet consumed by wild-type control or tas1r3-/- zebrafish in 30 min (n = 3).Supplemental Figure S9. The lipid metabolism in grass carp before or after the FHT from carnivory to herbivory. (A) Heat map of hepatic differentially expressed genes (DEGs) associated with lipid metabolism. (B) qPCR validation of RNA-seq results for lipid metabolism in grass carp before or after the FHT from carnivory to herbivory (n ≥ 4).