Cloning and heterologous expression of new xANO2 from Xenopus laevis

We have successfully isolated a novel anoctamin (xANO2), Ca²⁺-activated chloride channel (ANO1, TMEM16A), from Xenopus laevis. The cDNA sequence was determined to belong to the anoctamin family by comparison with the xTMEM16A sequence in a previous report. Full length cDNA synthesis was performed by repeating 5'- and 3'-rapid amplification of cDNA end (RACE). We successfully completed the entire cDNA sequence and transiently named this sequence xANO2. The xANO2 cDNA is 3884 base pair (bp) long and codes 980 amino acid (aa) proteins. According to an aa homology search using the Basic Local Alignment Search Tool (BLAST), xANO2 showed an overall identity of 92% to xTMEM16A (xANO1) independently sub-cloned in our laboratory. A primary sequence of xANO2 revealed typical characteristics of transmembrane proteins. In tissue distribution analysis, the gene products of anoctamins were ubiquitously detected by real-time PCR (RT-PCR). The expression profiles of each anoctamin were different among brain, oocytes, and digestive organs with relatively weak expression. To clarify the anoctamin activity, physiological studies were performed using the whole cell patch-clamp technique with HEK293T cells, enhanced green fluorescent protein (EGFP), and expression vectors carrying anoctamins. Characteristics typical of voltage-dependent chloride currents were detected in cells expressing both xANO2 and xTMEM16A but not with EGFP alone. Sensitive reactions to the anion channel blocker niflumic acid (NFA) were also revealed. Considering these results, xANO2 was regarded as a new TMEM16A belonging to the Xenopus anoctamin family.