the spindle pole body during mitosis, from where it is presumed that the 1919 Route de Mende, 34293 Montpellier signal for septum formation is delivered. Cdc11 mutants are defective in Cedex 5, France.SIN signaling, but the role of cdc11 in the pathway has remained enigmatic.

Digital holography microscopy (DHM) is an optical technique which provides phase images yielding quantitative information about cell structure and cellular dynamics. Furthermore, the quantitative phase images allow the derivation of other parameters, including dry mass production, density, and spatial distribution. We have applied DHM to study the dry mass production rate and the dry mass surface density in wild-type and mutant fission yeast cells. Our study demonstrates the applicability of DHM as a tool for label-free quantitative analysis of the cell cycle and opens the possibility for its use in high-throughput screening.

Recent reports suggest that mammalian embryonic coronary endothelium (CoE) originates from the sinus venosus and ventricular endocardium. However, the contribution of extracardiac cells to CoE is thought to be minor and nonsignificant for coronary formation. Using classic (Wt1 Cre ) and previously undescribed (G2-Gata4 Cre ) transgenic mouse models for the study of coronary vascular development, we show that extracardiac septum transversum/ proepicardium (ST/PE)-derived endothelial cells are required for the formation of ventricular coronary arterio-venous vascular connections. Our results indicate that at least 20% of embryonic coronary arterial and capillary endothelial cells derive from the ST/PE compartment. Moreover, we show that conditional deletion of the ST/PE lineage-specific Wilms' tumor suppressor gene (Wt1) in the ST/PE ofG2-Gata4 Cre mice and in the endothelium of Tie2 Cre mice disrupts embryonic coronary transmural patterning, leading to embryonic death. Taken together, our results demonstrate that ST/PE-derived endothelial cells contribute significantly to and are required for proper coronary vascular morphogenesis.T he coronary vascular system, whose function is necessary to sustain late embryonic and postnatal cardiac function, is formed by a complex network of blood vessels, including arteries, arterioles, capillaries, venules, and veins (1). Recent reports indicate that various sources of endothelial cells contribute to the mammalian embryonic coronary system (2-4). However, the specific fate and function of these different endothelial cell pools during coronary vascular morphogenesis is the subject of intense controversy (5).Two endocardial populations have been reported to participate in the building of the embryonic coronary vascular system. The first derives from the sinus venosus endocardium, which sprouts to give rise to the nascent Apelin + coronary vasculature (2). A careful analysis of this study suggests that the sinus venosus endocardium, which is able to vascularize subepicardial and myocardial heart layers, mainly provides a cellular scaffold for the development of coronary veins (CoV). Accordingly, a second source of coronary endothelium (CoE) has been identified in the ventricular endocardium (Nfatc1 + lineage), which contributes massively to coronary arterial (CoA) endothelium (3, 6).A third disputed source of CoE is the proepicardium (PE), a structure that comprises epicardial progenitor cells. The PE protrudes from the septum transversum (ST), a folding of the lateral mesoderm that initiates the separation of thoracic and abdominal cavities in mammals (7). Although in vivo cell tracing and in vitro culture of avian PE cells clearly shows that PE cells can differentiate into CoE (8, 9), data from studies in mammals claimed the contribution of PE to CoE is minor (10-12). The so-called "epicardial" Cre constructs used in these studies are based on the expression of genes such as Gata5, Tbx18, or Wilms' tumor suppressor (Wt1) ( Table S1), all of which are expressed by both PE and...