A Circadian Clock-Regulated Toggle Switch Explains AtGRP7 and AtGRP8 Oscillations in Arabidopsis thaliana

Schmal C, Reimann P, Staiger D. A Circadian Clock-Regulated Toggle Switch Explains AtGRP7 and AtGRP8 Oscillations in Arabidopsis thaliana. PLoS Computational Biology. 2013;9(3): e1002986.The circadian clock controls many physiological processes in higher plants and causes a large fraction of the genome to be expressed with a 24h rhythm. The transcripts encoding the RNA-binding proteins AtGRP7 (Arabidopsis thaliana Glycine Rich Protein 7) and AtGRP8 oscillate with evening peaks. The circadian clock components CCA1 and LHY negatively affect AtGRP7 expression at the level of transcription. AtGRP7 and AtGRP8, in turn, negatively auto-regulate and reciprocally cross-regulate post-transcriptionally: high protein levels promote the generation of an alternative splice form that is rapidly degraded. This clock-regulated feedback loop has been proposed to act as a molecular slave oscillator in clock output. While mathematical models describing the circadian core oscillator in Arabidopsis thaliana were introduced recently, we propose here the first model of a circadian slave oscillator. We define the slave oscillator in terms of ordinary differential equations and identify the model's parameters by an optimization procedure based on experimental results. The model successfully reproduces the pertinent experimental findings such as waveforms, phases, and half-lives of the time-dependent concentrations. Furthermore, we obtain insights into possible mechanisms underlying the observed experimental dynamics: the negative auto-regulation and reciprocal cross-regulation via alternative splicing could be responsible for the sharply peaking waveforms of the AtGRP7 and AtGRP8 mRNA. Moreover, our results suggest that the AtGRP8 transcript oscillations are subordinated to those of AtGRP7 due to a higher impact of AtGRP7 protein on alternative splicing of its own and of the AtGRP8 pre-mRNA compared to the impact of AtGRP8 protein. Importantly, a bifurcation analysis provides theoretical evidence that the slave oscillator could be a toggle switch, arising from the reciprocal cross-regulation at the post-transcriptional level. In view of this, transcriptional repression of AtGRP7 and AtGRP8 by LHY and CCA1 induces oscillations of the toggle switch, leading to the observed high-amplitude oscillations of AtGRP7 mRNA

Does a Bank’s Loan Screening and Monitoring Matter?

Loan screening, Monitoring, Announcement returns, G14, G21,

Debt raising and refinancing by Japanese REITs: information content in a credit crunch

This paper examines the information content of debt raising and refinancing activities of Real Estate Investment Trusts (REITs) in normal and tight credit markets. Based on a sample of 340 debt announcements made by REITs in Japan (J-REITs) between 2002 and 2011, we observe that they are associated with a positive stock price reaction, averaging 1.05 % over a 4-day window. Stratifying the sample into debt raising and debt refinancing, we find strong evidence that the positive economic gains associated with debt announcements flowed from the pool of debt refinancing announcements. They registered a significant mean return of 1.20 % over the 4-day window, as opposed to 0.07 % for the pool of debt raising activities. Further investigation shows that the positive market reaction to debt refinancing is more pronounced during the credit crunch of 2007 to 2009. Although debt refinancing does not lead to any change in the firm’s capital structure, it still contains valuable information about the firm’s prospect, especially in tight credit markets

Investors' valuation of global product design and development

Stock price responses to 170 announcements about global product design and development (GPDD) by NYSE, AMEX, and Nasdaq firms are significantly positive. This indicates that GPDD, which is fast becoming a strategic initiative of choice for multinational firms in the face of globalization and short time-to-market, is value-enhancing. The value enhancement is strong when announcing firms have a high level of information technology/systems infrastructure and a wide geographical spread of operation, and respond aggressively to their peers' strategic initiatives. Further, cross-sectional analyses show that firms' product market structure, their peers' competitive strategy posture, and whether they produce a good or a service, jointly determine the variation of excess returns attributable to global product development. Journal of International Business Studies (2003) 34, 457–472. doi:10.1057/palgrave.jibs.8400049