Embryonic development is tightly controlled. The clustered genes of the Hox family of homeobox proteins play an important part in regulating this development and also proliferation. They specify embryonic structures along the body axis, and are associated with normal and malignant cell growth. The cell-cycle regulator geminin controls replication by binding to the licensing factor Cdt1, and is involved in neural differentiation. Here, we show that murine geminin associates transiently with members of the Hox-repressing polycomb complex, with the chromatin of Hox regulatory DNA elements and with Hox proteins. Gain- and loss-of-function experiments in the chick neural tube demonstrate that geminin modulates the anterior boundary of Hoxb9 transcription, which suggests a polycomb-like activity for geminin. The interaction between geminin and Hox proteins prevents Hox proteins from binding to DNA, inhibits Hox-dependent transcriptional activation of reporter and endogenous downstream target genes, and displaces Cdt1 from its complex with geminin. By establishing competitive regulation, geminin functions as a coordinator of developmental and proliferative control.

It is well known that abscisic acid (ABA)-induced leaf senescence and premature leaf senescence negatively affect the yield of rice (Oryza sativa). However, the molecular mechanism underlying this relationship, especially the upstream transcriptional network that modulates ABA level during leaf senescence, remains largely unknown. Here, we demonstrate a rice NAC transcription factor, OsNAC2, that participates in ABA-induced leaf senescence. Overexpression of OsNAC2 dramatically accelerated leaf senescence, whereas its knockdown lines showed a delay in leaf senescence. Chromatin immunoprecipitation-quantitative PCR, dual-luciferase, and yeast one-hybrid assays demonstrated that OsNAC2 directly activates expression of chlorophyll degradation genes, OsSGR and OsNYC3. Moreover, ectopic expression of OsNAC2 leads to an increase in ABA levels via directly up-regulating expression of ABA biosynthetic genes (OsNCED3 and OsZEP1) as well as down-regulating the ABA catabolic gene (OsABA8ox1). Interestingly, OsNAC2 is upregulated by a lower level of ABA but downregulated by a higher level of ABA, indicating a feedback repression of OsNAC2 by ABA. Additionally, reduced OsNAC2 expression leads to about 10% increase in the grain yield of RNAi lines. The novel ABA-NAC-SAGs regulatory module might provide a new insight into the molecular action of ABA to enhance leaf senescence and elucidates the transcriptional network of ABA production during leaf senescence in rice.Senescence is the last stage of leaf development. During this period, various changes occur at the physiological, biochemical, and molecular levels. For example, macromolecules including lipids, proteins, and nucleic acids are hydrolyzed, which leads to disassembly of mitochondria and nuclei, and to cell death (Buchanan-Wollaston et al., 2005;Ulker et al., 2007). Although senescence is an active process to salvage nutrients from old tissues, precocious senescence will shorten the growth stage of crops and be unfavorable to agronomic production (Woo et al., 2013).The most distinguishing feature in leaf senescence is the yellowing phenotype, which is a visible marker of the degradation of macromolecules (Kim et al., 2006). The chlorophyll degradation pathway is one of the most characterized ones for macromolecule degradation in plants (Hörtensteiner, 2006). Overexpressing NON-YELLOW COLORING1 (NYC1) or NYC1-like genes in rice (Oryza sativa) can induce degradation of chlorophyll . A pph (encoding pheophytinase) mutant is abnormal in chlorophyll degradation during senescence and therefore exhibits a stay-green phenotype (Schelbert et al., 2009). Mutation of the PAO (Pheophorbide a oxygenase) gene leads to retention of chlorophyll in leaves during dark-induced senescence in Arabidopsis (Arabidopsis thaliana; Pruzinská et al., 2005). Recently, the highly conserved STAY-GREEN (SGR) in higher plants has been identified to be chloroplast-localized dechelatase (Shimoda et al., 2016).The senescence process is highly regulated by a range of important factors. It has been demon...

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In the mouse embryo, the aorta-gonad-mesonephros (AGM) region is considered to be the sole location for intraembryonic emergence of hematopoietic stem cells (HSCs). Here we report that, in parallel to the AGM region, the E10.5-E11.5 mouse head harbors bona fide HSCs, as defined by long-term, high-level, multilineage reconstitution and self-renewal capacity in adult recipients, before HSCs enter the circulation. The presence of hemogenesis in the midgestation head is indicated by the appearance of intravascular cluster cells and the blood-forming capacity of a sorted endothelial cell population. In addition, lineage tracing via an inducible VE-cadherin-Cre transgene demonstrates the hemogenic capacity of head endothelium. Most importantly, a spatially restricted lineage labeling system reveals the physiological contribution of cerebrovascular endothelium to postnatal HSCs and multilineage hematopoiesis. We conclude that the mouse embryonic head is a previously unappreciated site for HSC emergence within the developing embryo.

Plants respond to environmental stresses by altering gene expression, and several genes have been found to mediate stress-induced expression, but many additional factors are yet to be identified. OsNAP is a member of the NAC transcription factor family; it is localized in the nucleus, and shows transcriptional activator activity in yeast. Analysis of the OsNAP transcript levels in rice showed that this gene was significantly induced by ABA and abiotic stresses, including high salinity, drought and low temperature. Rice plants overexpressing OsNAP did not show growth retardation, but showed a significantly reduced rate of water loss, enhanced tolerance to high salinity, drought and low temperature at the vegetative stage, and improved yield under drought stress at the flowering stage. Microarray analysis of transgenic plants overexpressing OsNAP revealed that many stress-related genes were up-regulated, including OsPP2C06/OsABI2, OsPP2C09, OsPP2C68 and OsSalT, and some genes coding for stress-related transcription factors (OsDREB1A, OsMYB2, OsAP37 and OsAP59). Our data suggest that OsNAP functions as a transcriptional activator that plays a role in mediating abiotic stress responses in rice.