title: Three isoforms of a hepatocyte nuclear factor-4 transcription factor with tissue- and stage-specific expression in the adult mosquito.
abstract: We cloned three isoforms of hepatocyte nuclear factor-4 (HNF-4) from the mosquito Aedes aegypti, designated AaHNF-4a, AaHNF-4b, and AaHNF-4c. AaHNF-4a and AaHNF-4b are typical members of the HNF-4 subfamily of nuclear receptors with high amino acid conservation. They differ in N-terminal regions and exhibit distinct developmental profiles in the female mosquito fat body, a metabolic tissue functionally analogous to the vertebrate liver. The AaHNF-4b mRNA is predominant during the previtellogenic and vitellogenic phases, while the AaHNF-4a mRNA is predominant during the termination phase of vitellogenesis, coinciding with the onset of lipogenesis. The third isoform, AaHNF-4c, lacks part of the A/B and the entire C (DNA-binding) domains. The AaHNF-4c transcript found in the fat body during the termination of vitellogenesis may serve as a transcriptional inhibitor. Both AaHNF-4a and AaHNF-4b bind to the cognate DNA recognition site in electrophoretic mobility shift assay. Dimerization of AaHNF-4c with other mosquito HNF-4 isoforms or with mammalian HNF-4 prevents binding to the HNF-4 response element. In transfected human 293T cells, AaHNF-4c significantly reduced the transactivating effect of the human HNF-4alpha1 on the apolipoprotein CIII promoter. Electrophoretic mobility shift assay confirmed the presence of HNF-4 binding sites upstream of A. aegypti vg and vcp, two yolk protein genes expressed in the female mosquito fat body during vitellogenesis. Therefore, HNF-4, an important regulator of liver-specific genes, plays a critical role in the insect fat body.
authors.affiliation: Program in Genetics and Department of Entomology, Michigan State University, East Lansing, Michigan 48824-1115, USA.
authors.forename: M Z
authors.initials: MZ
authors.lastname: Kapitskaya
authors.forename: N T
authors.initials: NT
authors.lastname: Dittmer
authors.forename: K W
authors.initials: KW
authors.lastname: Deitsch
authors.forename: W L
authors.initials: WL
authors.lastname: Cho
authors.forename: D G
authors.initials: DG
authors.lastname: Taylor
authors.forename: T
authors.initials: T
authors.lastname: Leff
authors.forename: A S
authors.initials: AS
authors.lastname: Raikhel
mesh_terms: D000330:Aedes / Q000254:growth & development / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D015342:DNA Probes; D005260:Female; D017228:Hepatocyte Growth Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007536:Isomerism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D015342:DNA Probes; D012333:RNA, Messenger; D012097:Repressor Proteins; D017228:Hepatocyte Growth Factor