Identification of new M23A mRNA of mouse aquaporin-4 expressed in brain, liver, and kidney.
Aquaporins (AQPs) belong to a transmembrane protein family of water channels that are permeable to water by the osmotic gradient. There are two isoforms of mouse AQP4 - M1 and M23. Their balance in the cell determines water permeability of the plasma membrane. These two isoforms are encoded by three mRNAs: M1 isoform is encoded by M1 mRNA and M23 isoform is encoded by M23 and M23X mRNAs. Here we found a new fourth mRNA of mouse AQP4 - M23A mRNA. The start of transcription is different for M23A mRNA from all the known AQP4 mRNAs. The 5'-untranslated region (5'-UTR) of M23A mRNA is encoded by four new exons (A, B, C, and D), which are located in the 5' region from exon-0 of the AQP4 gene. Alternative splicing between the exons-A, -B, -C, and -D leads to formation of multiple variants of M23A mRNA. We cloned six of these variants, all of which code full length M23 isoform of AQP4. Using RT-PCR we detected tissue-specific expression of the new M23A and already known M23, M23X, and M1 mRNAs. The M23A mRNA is expressed mostly in kidney, liver, and brain. Analysis of mRNA 5'-UTR structure showed low translation efficacy for M1 mRNA in comparison with high translation efficacy for M23A, M23X, and M23 mRNAs. We propose that AQP4 expression is controlled tissue-specifically by independent promoters. Thus multiple AQP4 mRNAs may allow long-term regulation of the balance between M1 and M23 AQP4 isoforms in the cell and thus water permeability of the plasma membrane.
Institute of Chemical Biology and Fundamental Medicine, Siberian Division of the Russian Academy of Sciences, pr. Lavrentieva 8, 630090 Novosibirsk, Russia. alikina@niboch.nsc.ru
T Yu
TY
Alikina
N B
NB
Illarionova
S M
SM
Zelenin
A A
AA
Bondar
D020121:5' Untranslated Regions; D017398:Alternative Splicing; D000818:Animals; D051401:Aquaporin 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D003001:Cloning, Molecular; D005091:Exons; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D017422:Sequence Analysis, DNA
D020121:5' Untranslated Regions; D051401:Aquaporin 4; D020033:Protein Isoforms; D012333:RNA, Messenger