Molecular cloning of two bovine aquaporin-4 cDNA isoforms and their expression in brain endothelial cells

Two cDNA isoforms of bovine aquaporin-4 (bAQP4-A and bAQP4-B) were newly is olated. Sequence analysis of both cDNAs revealed open reading frames of 972 (bAQP4-A) and 906 nucleotides (bAQP4-B) with deduced proteins of 323 (bAQP 4-A) and 301 amino acid residues (bAQP4-B). Partial 5'-genomic sequence ana lysis showed that the 5'-noncoding sequences specific to bAQP4-A and -B tra nscripts were contained in distinct exons, exon 0 for bAQP4-A and new exon X for bAQP4-B. RNase protection assay demonstrated the definite expression of both isoforms in bovine brain. The deduced amino acid sequence of bAQP4- A was highly homologous to the human (97%), rat (95%), and mouse (93%) AQP4 . Reverse transcription-PCR detected the expression of AQP4 mRNAs in bovine brain endothelial cells as well as in a variety of bovine organs such as b rain, lung, spleen, and kidney. Northern blot analysis indicated that a 6.0 kb message is predominantly expressed in bovine brain and lung. (C) 1999 E lsevier Science B.V. All rights reserved.