To search for genes that promote hematopoietic development from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs), we overexpressed several known hematopoietic regulator genes in hESC/iPSC-derived CD34 ؉ CD43 ؊ endothelial cells (ECs) enriched in hemogenic endothelium (HE). Among the genes tested, only Sox17, a gene encoding a transcription factor of the SOX family, promoted cell growth and supported expansion of CD34 ؉ CD43 ؉ CD45 ؊/low cells expressing the HE marker VE-cadherin. SOX17 was expressed at high levels in CD34 ؉ CD43 ؊ ECs compared with low levels in CD34 ؉ CD43 ؉ CD45 ؊ pre-hematopoietic progenitor cells (pre-HPCs) and CD34 ؉ CD43 ؉ CD45 ؉ HPCs. Sox17-overexpressing cells formed semiadherent cell aggregates and generated few hematopoietic progenies. However, they retained hemogenic potential and gave rise to hematopoietic progenies on inactivation of

Studying the mirror symmetry of a Calabi-Yau threefold X of the Reye congruence in P 4 , we conjecture that X has a non-trivial Fourier-Mukai partner Y . We construct Y as the double cover of a determinantal quintic in P 4 branched over a curve. We also calculate BPS numbers of both X and Y (and also a related Calabi-Yau complete intersectionX 0 ) using mirror symmetry.1 Recently, the derived category of the classical Reye congruence has been studied in [IKu,Ku3].

SUMMARYVisualization of the spatiotemporal pattern of cell division is crucial to understand how multicellular organisms develop and how they modify their growth in response to varying environmental conditions. The mitotic cell cycle consists of four phases: S (DNA replication), M (mitosis and cytokinesis), and the intervening G1 and G2 phases; however, only G2/M-specific markers are currently available in plants, making it difficult to measure cell cycle duration and to analyze changes in cell cycle progression in living tissues. Here, we developed another cell cycle marker that labels S-phase cells by manipulating Arabidopsis CDT1a, which functions in DNA replication origin licensing. Truncations of the CDT1a coding sequence revealed that its carboxy-terminal region is responsible for proteasome-mediated degradation at late G2 or in early mitosis. We therefore expressed this region as a red fluorescent protein fusion protein under the S-specific promoter of a histone 3.1-type gene, HISTONE THREE RELATED2 (HTR2), to generate an S/G2 marker. Combining this marker with the G2/M-specific CYCB1-GFP marker enabled us to visualize both S to G2 and G2 to M cell cycle stages, and thus yielded an essential tool for time-lapse imaging of cell cycle progression. The resultant dual-color marker system, Cell Cycle Tracking in Plant Cells (Cytrap), also allowed us to identify root cells in the last mitotic cell cycle before they entered the endocycle. Our results demonstrate that Cytrap is a powerful tool for in vivo monitoring of the plant cell cycle, and thus for deepening our understanding of cell cycle regulation in particular cell types during organ development.

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