Extraoral expression and characterization of bitter taste receptors in (Mexican tetra fish).

The chemical senses of olfaction and taste are well developed in fish and play a vital role in its various activities such as navigation, mate recognition, and food detection. The small teleost fish consists of interfertile river-dwelling and cave-dwelling populations, referred to as "surface fish" and "cavefish" respectively. An important anatomical feature of cavefish is the lack of eyes leading them to be referred to as blind fish and suggesting an enhanced functional role for other senses such as taste. In this study, we characterize the expression of bitter taste receptors (T2Rs or ) in and investigate their functionality in a heterologous expression system. The genome database of (ensemble and NCBI) showed 7 , among these , and are well characterized in humans and mice but not in . Therefore, the 4 were selected for further analysis and their expression in was confirmed by in situ hybridization and RT-PCR in early developmental stages. These are expressed in various oral and extraoral organs (liver, fins, jaws, and gills) in , and has maximum expression and is localized throughout the fish body. Using the heterologous expression of T2Rs in HEK293T cells coupled with cell-based calcium mobilization assays, we show that T2Rs are activated by commonly used fish food and known bitter agonists, including quinine. This study provides novel insights into the extraoral expression of T2Rs in and suggests their importance in extraoral food detection.