In a search for novel genes involved in the hypothalamic control of body energy homeostasis bioinformatic tools were applied. Analysis of the presence of structural features characteristic for secretory peptides was used as a first step in the identification of novel neuropeptides, and was followed by analysis of expression patterns. The gene product previously named TAFA5 was identified during this process. The overall mRNA expression pattern of TAFA5 was assessed using quantitative PCR on rat cDNA libraries. Furthermore, the brain mRNA and polypeptide expression patterns were examined in rats using in situ hybridization and immunohistochemistry. Our results substantiate previous findings that TAFA5 is mainly expressed in the central nervous system. Furthermore, we found TAFA5 mRNA to be highly expressed in the hypothalamic paraventricular nucleus (PVN) where it co-localized with vasopressin and oxytocin in magno- and parvocellular neurons. Immunohistochemical analysis revealed TAFA5 immunoreactivity in the PVN in accordance with the in situ hybridization data. Given the high levels of expression in the PVN, it was investigated whether TAFA5 mRNA levels were affected by fasting or dehydration. Interestingly, it was observed that TAFA5 mRNA was specifically down-regulated in the PVN following water deprivation. Based on our findings we suggest that TAFA5 may be involved in the regulation of fluid homeostasis.
