The allocation of time to crime: A simple diagrammatical exposition

In his seminal article on the allocation of time to crime, Isaac Ehrlich (1973) derives five interesting theoretical results. He uses a state-preference diagram to derive one result, retreating to mathematics for deriving the remaining four results. This note shows that all five results can easily be derived from an alternative and simpler diagrammatical exposition that involves intersection of curves rather than tangency between curves.

Auditing ghosts by prosperity signals

Ghosts are economic agents who evade taxes by failing to file a return. Knowing nothing about them, the tax agency is unable to track them down through audit strategies which are based on reported income. The present paper develops a simple model of the audit decision for a ghost-busting tax agency which bases its audit strategy on signals of prosperous living, such as ownership of high-quality housing. Ghosts have a preference for high-quality housing, but may opt to own houses of a lower quality so as to escape detection. The paper compares the optimal audit rules and net tax collection under signal and blind auditing of the non-declaring population, deriving conditions under which each strategy will dominate the other.

Dissection of a DNA-damage-induced transcriptional network using a combination of microarrays, RNA interference and computational promoter analysis

BACKGROUND: Gene-expression microarrays and RNA interferences (RNAi) are among the most prominent techniques in functional genomics. The combination of the two holds promise for systematic, large-scale dissection of transcriptional networks. Recent studies, however, raise the concern that nonspecific responses to small interfering RNAs (siRNAs) might obscure the consequences of silencing the gene of interest, throwing into question the ability of this experimental strategy to achieve precise network dissections. RESULTS: We used microarrays and RNAi to dissect a transcriptional network induced by DNA damage in a human cellular system. We recorded expression profiles with and without exposure of the cells to a radiomimetic drug that induces DNA double-strand breaks (DSBs). Profiles were measured in control cells and in cells knocked-down for the Rel-A subunit of NFκB and for p53, two pivotal stress-induced transcription factors, and for the protein kinase ATM, the major transducer of the cellular responses to DSBs. We observed that NFκB and p53 mediated most of the damage-induced gene activation; that they controlled the activation of largely disjoint sets of genes; and that ATM was required for the activation of both pathways. Applying computational promoter analysis, we demonstrated that the dissection of the network into ATM/NFκB and ATM/p53-mediated arms was highly accurate. CONCLUSIONS: Our results demonstrate that the combined experimental strategy of expression arrays and RNAi is indeed a powerful method for the dissection of complex transcriptional networks, and that computational promoter analysis can provide a strong complementary means for assessing the accuracy of this dissection

Tax evasion and exchange equity: a reference-dependent approach

The standard portfolio model of tax evasion with a public good produces the perverse conclusion that when taxpayers perceive the public good to be under-/overprovided, an increase in the tax rate increases/decreases evasion. The author treats taxpayers as thinking in terms of gains and losses relative to an endogenous reference level, which reflects perceived exchange equity between the value of taxes paid and the value of public goods supplied. With these alternative behavioral assumptions, the author overturns the aforementioned result in a direction consistent with the empirical evidence. The author also finds a role for relative income in determining individual responses to a change in the marginal rate of tax

Venous-derived angioblasts generate organ-specific vessels during embryonic development

Formation and remodeling of vascular beds are complex processes orchestrated by multiple signaling pathways. While it is well accepted that vessels of a particular organ display specific features that enable them to fulfill distinct functions, the embryonic origins of tissue-specific vessels, as well as the molecular mechanisms regulating their formation, are poorly understood. The subintestinal plexus of the zebrafish embryo comprises vessels that vascularize the gut, liver and pancreas, and as such represents an ideal model to investigate the early steps of organ-specific vessel formation. Here we show that both arterial and venous components of the subintestinal plexus originate from a pool of specialized angioblasts residing in the floor of the Posterior Cardinal Vein (PCV). Using live imaging of zebrafish embryos, in combination with photoconvertable transgenic reporters, we demonstrate that these angioblasts undergo two phases of migration and differentiation. Initially, a subintestinal vein (SIV) forms and expands ventrally through a bone morphogenetic protein (BMP)-dependent step of collective migration. Concomitantly, a VEGF-dependent shift in the directionality of migration, coupled to the upregulation of arterial markers is observed, which culminates with the generation of the supraintestinal artery (SIA). Altogether our results establish the zebrafish subintestinal plexus as an advantageous model for the study of organ-specific vessel development, and provide new insights into the molecular mechanisms controlling its formation. More broadly, our findings suggest that PCV-specialized angioblasts contribute not only to the formation of the early trunk vasculature, but also to the establishment of late forming-, tissue specific vascular beds

Venous-derived angioblasts generate organ-specific vessels during zebrafish embryonic development

open11siFormation and remodeling of vascular beds are complex processes orchestrated by multiple signaling pathways. Although it is well accepted that vessels of a particular organ display specific features that enable them to fulfill distinct functions, the embryonic origins of tissue-specific vessels and the molecular mechanisms regulating their formation are poorly understood. The subintestinal plexus of the zebrafish embryo comprises vessels that vascularize the gut, liver and pancreas and, as such, represents an ideal model in which to investigate the early steps of organ-specific vessel formation. Here, we show that both arterial and venous components of the subintestinal plexus originate from a pool of specialized angioblasts residing in the floor of the posterior cardinal vein (PCV). Using live imaging of zebrafish embryos, in combination with photoconvertable transgenic reporters, we demonstrate that these angioblasts undergo two phases of migration and differentiation. Initially, a subintestinal vein forms and expands ventrally through a Bone Morphogenetic Protein-dependent step of collective migration. Concomitantly, a Vascular Endothelial Growth Factor-dependent shift in the directionality of migration, coupled to the upregulation of arterial markers, is observed, which culminates with the generation of the supraintestinal artery. Together, our results establish the zebrafish subintestinal plexus as an advantageous model for the study of organ-specific vessel development and provide new insights into the molecular mechanisms controlling its formation. More broadly, our findings suggest that PCV-specialized angioblasts contribute not only to the formation of the early trunk vasculature, but also to the establishment of late-forming, tissue-specific vascular beds.openHen, Gideon; Nicenboim, Julian; Mayseless, Oded; Asaf, Lihee; Shin, Masahiro; Busolin, Giorgia; Hofi, Roy; Almog, Gabriella; Tiso, Natascia; Lawson, Nathan D.; Yaniv, KarinaHen, Gideon; Nicenboim, Julian; Mayseless, Oded; Asaf, Lihee; Shin, Masahiro; Busolin, Giorgia; Hofi, Roy; Almog, Gabriella; Tiso, Natascia; Lawson, Nathan D.; Yaniv, Karin