ABSTRACT
Members of the enhancer of split- and hairy-related protein (SHARP) family, SHARP-1 and SHARP-2, are basic helix-loop-helix transcriptional repressors and belong to the clock genes. In this study, an effect of retinoic acid (RA) on the SHARP family gene expression in the differentiated cells was examined. RA rapidly and temporarily induced the SHARP-2 mRNA expression in hepatic H4IIE cells. Then, whether the SHARP-2 mRNA expression is altered by dexamethasone (Dex), insulin, and the combination of RA and Dex or RA and insulin was examined. Dex had different effects on the expression of SHARP-2 mRNA in the presence or absence of RA. Then, the molecular mechanisms were investigated using inhibitors of various signaling molecules. The RA-induction of SHARP-2 mRNA level was mainly inhibited by LY294002, staurosporine, and actinomycin D, respectively. Finally, whether RA acts on the transcriptional regulatory region of the SHARP-2 gene was analysed using luciferase reporter gene assay. At least two RA-responsive regions were mapped at the nucleotide sequences between -3,700 and -1,600 of the SHARP-2 gene. In addition, this effect was dependent on the RA receptor and retinoid X receptor. Thus, we conclude that RA stimulated transcription of the SHARP-2 gene via multiple pathways.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/genetics , Homeodomain Proteins/genetics , Transcription, Genetic/drug effects , Tretinoin/pharmacology , Animals , Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Line , Dexamethasone/pharmacology , Hep G2 Cells , Hepatocytes/metabolism , Homeodomain Proteins/metabolism , Humans , Insulin/pharmacology , RNA, Messenger/genetics , Rats , Receptors, Retinoic Acid/metabolism , Retinoid X Receptors/metabolism , Signal Transduction/drug effects , Tretinoin/metabolismABSTRACT
Preliminary observation of the flights of swallowtail butterfly Papilio xuthus revealed that its dihedral angle is larger than 30 degrees and that the section of its left hind wing close to its body and the counterpart of its right hind wing actually clap and form a "vertical tail". In this study, the effects of these two features on the lateral-directional dynamic flight stability of these butterflies were analyzed theoretically and revealed the following: (a) when the dihedral angle is larger than 30 degrees , the lateral-directional motion of the swallowtail becomes stable; (b) the vertical tail stabilizes the dutch roll mode; (c) the effects of the dihedral angle on the roll and spiral modes of a swallowtail are qualitatively the same as those of a meter-sized airplane; and (d) with increasing dihedral angle, the stability of the dutch roll mode decreases for a meter-sized airplane with vertical and horizontal tails but increases for the swallowtail. A possible explanation for the latter effect is the smaller Reynolds number of the insect that causes the drag coefficient of the swallowtail wings to increase more rapidly with an increasing angle of attack compared to a large airplane.
