The expression patterns of FLCN, FNIP1 and FNIP2 in human tissues were determined by Hasumi et al. (2008) using real-time PCR. The expression patterns of these proteins were generally similar, and consistently high in specific tissues, such as the muscles, nasal mucosa, salivary gland and uvula, suggesting that FLCN, FNIP1 and FNIP2 may work together in these organs. However, FNIP2 expression was higher relative to FNIP1 in fat, liver and pancreas, which suggests that FNIP2 may have a specific function in these metabolic tissues (Hasumi et al., 2008). FLCN/FNIP1 and FLCN/FNIP2 dimers have been shown to co-localise in the cytoplasm in a reticular pattern (Baba et al., 2006; Hasumi et al., 2008; Takagi et al., 2008). Co-expression studies of N-terminal tagged FLCN, FNIP1 and FNIP2 indicate that both FNIPs regulate the cytoplasmic distribution of FLCN (Baba et al., 2006; Hasumi et al., 2008; Takagi et al., 2008). When tagged FNIP2 constructs are expressed alone, FNIP2 is seen to be distributed within the cytoplasm of cells, showing more condensed features around the nucleus. Conversely, when tagged FLCN constructs are expressed alone, they appear to be found mainly in the nucleus (Takagi et al., 2008). However, when FNIP2 and FLCN are co-expressed they co-localise together in the cytoplasm in a reticular pattern, which is similar to the co-localisation of FNIP1 and FLCN (Baba et al., 2006; Hasumi et al., 2008; Takagi et al., 2008).
