Mutations resulting in embryonic or early postnatal lethality could mask the activities of any gene in unrelated and temporally distinct developmental pathways. Targeted inactivation of the transcription factor GATA-2 gene leads to mid-gestational death as a consequence of hematopoietic failure. We show here that a 250 kbp GATA-2 yeast artificial chromosome (YAC) is expressed strongly in both the primitive and definitive hematopoietic compartments, while two smaller YACs are not. This largest YAC also rescues hematopoiesis in vitro and in vivo, thereby localizing the hematopoietic regulatory cis element(s) to between 100 and 150 kbp 5Ј to the GATA-2 structural gene. Introducing the YAC transgene into the GATA-2 -/-genetic background allows the embryos to complete gestation; however, newborn rescued pups quickly succumb to lethal hydroureternephrosis, and display a complex array of genitourinary abnormalities. These findings reveal that GATA-2 plays equally vital roles in urogenital and hematopoietic development.

GATA-2, a transcription factor that has been shown to play important roles in multiple organ systems during embryogenesis, has been ascribed the property of regulating the expression of numerous endothelium-specific genes. However,the transcriptional regulatory hierarchy governing Gata2 activation in endothelial cells has not been fully explored. Here, we document GATA-2 endothelial expression during embryogenesis by following GFP expression in Gata2-GFP knock-in embryos. Using founder transgenic analyses, we identified a Gata2 endothelium enhancer in the fourth intron and found that Gata2 regulation by this enhancer is restricted to the endocardial, lymphatic and vascular endothelium. Whereas disruption of three ETS-binding motifs within the enhancer diminished its activity, the ablation of its single E box extinguished endothelial enhancer-directed expression in transgenic mice. Development of the endothelium is known to require SCL(TAL1), and an SCL-E12 (SCL-Tcfe2a) heterodimer can bind the crucial E box in the enhancer in vitro. Thus, GATA-2 is expressed early in lymphatic, cardiac and blood vascular endothelial cells, and the pan-endothelium-specific expression of Gata2 is controlled by a discrete intronic enhancer.

In phase I clinical trials, experimental drugs are administered to healthy volunteers in order to establish their safety and to explore the relationship between the dose taken and the concentration found in plasma. Each volunteer receives a series of increasing single doses. In this paper a Bayesian decision procedure is developed for choosing the doses to give in the next round of the study, taking into account both prior information and the responses observed so far. The procedure seeks the optimal doses for learning about the dose-concentration relationship, subject to a constraint which reduces the risk of administering dangerously high doses. Individual volunteers receive more than one dose, and the pharmacokinetic responses observed are, after logarithmic transformation, treated as approximately normally distributed. Thus data analysis can be achieved by fitting linear mixed models. By expressing prior information as 'pseudo-data', and by maximizing over posterior distributions rather than taking expectations, a procedure which can be implemented using standard mixed model software is derived. Comparisons are made with existing approaches to the conduct of these studies, and the new method is illustrated using real and simulated data.To whom correspondence should be addressed.

This paper reviews Bayesian dose-escalation procedures for phase I clinical trials and describes a systematic approach to their implementation. The methodology is constructed for studies in which each subject is administered a single dose of an experimental drug and provides a single binary response, referred to here as toxicity or no toxicity. It is assumed that the probability of toxicity rises with log dose of drug according to a logistic regression yi' ghri "Or, phD John Whitobiad, PhD model.It is suggested that the choice of suitable prior distributions be aided ria graphical rep-

GATA-3 is expressed in a temporally dynamic manner and fulfills vital functions during vertebrate fetal development. Homozygous mGATA-3 mutant embryos die at midgestation, thus complicating the analysis of its contribution to the development of specific cell fates in the many tissues where it is expressed during embryogenesis. We show here that the elements controlling GATA-3 regulation can be precisely refined, using transgenic mice, to discrete cis-acting domains: within 6 kb surrounding the transcriptional initiation site, separate sequences were found to control the expression of mGATA-3 in early muscle masses, in a subset of PNS neurons, in the genital tubercle, and in the branchial arches. The branchial arch regulatory element is particularly robust and was refined to a discrete enhancer sequence lying between nt -2832 and -2462 from the transcription initiation site. The enhancer contains potential binding sites for many well-characterized transcription factors, suggesting that mGATA-3 transcriptional activity may be regulated by these proteins (or related family members) in the mesenchyme of the arches that contribute to formation of the jaw. These studies show that discrete regulatory elements required for the elaboration of complex developmental programs can be individually localized, suggesting that the developmentally transient expression of individual transcription factors collaboratively contributes to the temporal and spatial pattern of cellular differentiation leading to the formation of adult anatomy.