Identification of intestinal phosphate transporters in fishes and shellfishes

摘要

Phosphorus (P) excreted from aquaculture systems pollutes aquatic environment. Reducing P output requires reducing P input in the feeds. Reducing P in feeds, however, increases the risk of P deficiency in fish. Thus, diagnosis of P deficiency in fish will be important to avoid chronic P deficiency. To detect incipient P deficiency, a sensitive method is needed. Previously, in trout, inorganic P transporters (NaPi) in the intestine have been shown to respond rapidly to early P deficiency. For other fishes, however, little is known about the NaPi sequences, not to mention their dietary responses. In this study, intestinal NaPi sequences were isolated anew in 23 fish species, including major aquaculture species. Also, NaPi-like sequences were isolated from three molluscan species. Phylogenetic analysis of the NaPi sequences showed reasonable agreement with known evolutionary relationships. Tissue distribution of NaPi messenger RNA (mRNA) was studied in rainbow trout, crucian carp, and tilapia by real-time reverse-transcription polymerase chain reaction (RT-PCR), which revealed distribution of NaPi mRNA in several tissues other than the intestine. Acute, but not chronic, dietary P restriction increased (P = 0.01) NaPi mRNA abundance by twofold in crucian carp intestine.