TRANSLATED ANTISENSE PRODUCT OF THE NA PHOSPHATE COTRANSPORTER (NAPI-II)/

The homeostasis of P-i in marine teleosts is maintained by renal P-i s ecretion as well as by P-i reabsorption. A Na/P-i co-transport system belonging to the NaPi-II protein family is instrumental in tightly con trolled renal P-i handling in mammals and fish. We have isolated an Na Pi-II related cDNA from winter flounder. It was cloned from a female g onad cDNA library and is 624 bp long. The transcript is expressed in f emale and male flounder gonads as well as in kidney and intestine, alt hough at very low levels. RNase H digestion experiments revealed an op posite orientation of the transcript with regard to NaPi-II-related mR NA. The anti-sense orientation was confirmed by genomic sequence analy sis and Southern blotting. Alluding to the sense transcript, the anti- sense transcript was denoted IPAN. The open reading frame of IPAN enco des a basic protein of 68 amino acid residues. Immunohistochemistry co nfined the anti-sense related protein, Ipan, to a submembranous compar tment of immature oocytes, suggesting a role in oocyte development. In kidney and intestine Ipan is partly co-localized with the Na/P-i co-t ransporter, implying a regulatory function for the anti-sense protein. However, direct protein-protein interaction could not be established. The existence of a putative open reading frame in other species exten ds the biological significance of the novel protein.