The Hippo/YAP pathway plays an important role in animal organ size control, which it exerts by regulating tissue proliferation and apoptosis rates as a response to developmental cues, cell contact, and density. With the ever increasing advance in genome sequencing and analysis tools, our understanding of the animal world and its evolution has greatly increased in the recent years. We used bioinformatic tools to study the evolution of the Hippo/YAP pathway focusing on the transcriptional coactivator YAP, which is a pivotal effector of the pathway. The aim was to establish the origin and mode of development of YAP and its pathway in the animal world. Some pathway members can be already identified in single-celled eukaryotes like the yeast that have preceded multicellular animals. Interestingly, we can find most of the components that are present in human in the sea-anemone Nematostella, which belongs to a very basal group of metazoans, the cnidarians. All the major domains of YAP have been conserved between cnidarians and mammals, and YAP can be identified even in the more basal placozoan clade. We show a very high degree of conservation in regions such as the WW and the TEAD-binding domains, TEAD being the major DNA-binding partner of YAP. Remarkably, we found that the location of an intron in the WW1 genomic region has been invariant along an evolutionary span of over 700 My. We have followed the evolutionary changes in YAP and in other main components of the pathway from the first metazoans such as sponges, described the phylogenetic relationships between the YAP genes and indicated where YAP and other components have been secondarily lost. Evidence is provided that YAP and its binding partner TEAD demonstrate strong coevolution. This gives further support for the importance of the TEAD-YAP association. Beyond contributing to an understanding of the evolutionary history of this pathway, we have provided insights into the "birth" of this pathway, its functions and its mode of operation in animals with different body plans, development, and life styles.

Plants, like many other organisms, have endogenous biological clocks that enable them to organize their physiological, metabolic and developmental processes so that they occur at optimal times. The best studied of these biological clocks are the circadian systems that regulate daily (∼ 24 h) rhythms. At the core of the circadian system in every organism are oscillators responsible for generating circadian rhythms. These oscillators can be entrained (set) by cues from the environment, such as daily changes in light and temperature. Completing the circadian clock model are the output pathways that provide a link between the oscillator and the various biological processes whose rhythms it controls. Over the past few years there has been a tremendous increase in our understanding of the mechanisms of the oscillator and entrainment pathways in plants and many useful reviews on the subject. In this review we focus on the output pathways by which the oscillator regulates rhythmic plant processes. In the first part of the review we describe the role of the circadian system in regulation at all stages of a plant's development, from germination and growth to reproductive development as well as in multiple cellular processes. Indeed, the importance of a circadian clock for plants can be gauged by the fact that so many facets of plant development are under its control. In the second part of the review we describe what is known about the mechanisms by which the circadian system regulates these output processes.

The YAP1 gene encodes a potent new oncogene and stem cell factor. However, in some cancers, the YAP1 gene plays a role of tumor suppressor. At present, the gene and its products are intensely studied and its cDNAs are used as transgenes in cellular and animal models. Here, we report 4 new potential mRNA splicing isoforms of the YAP1 gene, bringing the total number of isoforms to 8. We detected all 8 YAP1 isoforms in a panel of human tissues and evaluated the expression of the longest isoform of YAP1 (YAP1-2δ) using Real Time PCR. All YAP1 isoforms are barely detectable in human leukocytes compared to fair levels of expression found in other human tissues. We analyzed the structure of the genomic region that gave rise to alternatively spliced YAP1 transcripts in different metazoans. We found that YAP1 isoforms, which utilize exon 6 emerged in evolution with the appearance of amniotes. Interestingly, 6 YAP1 isoforms, which contain the exon 5 extension, exon 6 or both would have their leucine zipper region disrupted in the predicted protein product, compared to the intact leucine zipper found in two YAP1 (α) isoforms. This observation has direct functional ramifications for YAP1 signaling. We also propose a normalized nomenclature for the mRNA splice variants of YAP1 gene, which should aid in the characterization of signaling differences among the potential protein products of the YAP1 gene.

As an adaptation to life in a world with predictable daily changes, most eukaryotes and some prokaryotes have endogenous circadian (approximately 24 h) clocks. In plants, the circadian clock regulates a diverse range of cellular and physiological events from gene expression and protein phosphorylation to cellular calcium oscillations, hypocotyl growth, leaf movements, and photoperiod-dependent flowering. In Arabidopsis (Arabidopsis thaliana), as in other model organisms, such as Drosophila (Drosophila melanogaster) and mice, circadian rhythms are generated by molecular oscillators that consist of interlocking feedback loops involving a number of elements. CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYLS (LHY) are closely related single myb transcription factors that have been identified as key elements in the Arabidopsis oscillator. Research in other model organisms has shown that posttranslational regulation of oscillator components plays a critical role in the generation of the approximately 24-h cycles. To examine the role of posttranslational regulation of CCA1 and LHY in the Arabidopsis oscillator, we generated transgenic plants with tagged CCA1 and LHY under the control of their own promoters. We have shown that these tagged proteins are functional and can restore normal circadian rhythms to CCA1-and LHY-null plants. Using the tagged proteins, we demonstrate that CCA1 can form both homodimers and heterodimers with LHY. Furthermore, we also show that CCA1 is localized to the nucleus in vivo and that there is no significant delay between the translation of CCA1 and its translocation to the nucleus. We discuss our findings in the context of the functioning of the Arabidopsis oscillator.The circadian, approximately 24 h, clock has an enormous influence on the biology of plants and controls a plethora of processes, including hypocotyl growth, shade avoidance, leaf movements, scent production, and stomatal opening (Yakir et al., 2007). Consistent with the role of the circadian clock in the regulation of a wide range of activities, transcription from approximately one-third of the genome (including noncoding genes) of the model plant Arabidopsis (Arabidopsis thaliana) is under circadian control (Michael and McClung, 2003; Covington et al., 2008;Michael et al., 2008;Hazen et al., 2009). In addition, the circadian clock serves as a timekeeper to regulate daylengthdependent processes, such as flowering time and tuberization. The circadian systems responsible for generating circadian rhythms are ubiquitous in eukaryotes and have also been found in some prokaryotes (Dunlap, 1999). Conceptually, a circadian system can be divided into three parts: the oscillator mechanism, input pathways, and output pathways. Interestingly, although their components differ, the basic oscillator mechanism appears to be well conserved in all the eukaryotic model organisms that have been studied (Dunlap, 2006). Oscillators are comprised of interlocking positive/negative feedback loops made from clock proteins that control t...

SUMMARYThe circadian system of plants regulates a wide range of rhythmic physiological and cellular output processes with a period of about 24 h. The rhythms are generated by an oscillator mechanism that, in Arabidopsis, consists of interlocking feedback loops of several components including CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1 (TOC1) and CCA1 HIKING EXPEDITION (CHE). Over recent years, researchers have gained a detailed picture of the clock mechanism at the resolution of the whole plant and several tissue types, but little information is known about the specificities of the clock mechanism at the level of individual cells. In this paper we have addressed the question of cell-typespecific differences in circadian systems. Using transgenic Arabidopsis plants with fluorescence-tagged CCA1 to measure rhythmicity in individual leaf cells in intact living plants, we showed that stomatal guard cells have a different period from surrounding epidermal and mesophyll leaf cells. By comparing transcript levels in guard cells with whole plants, we identified differences in the expression of some oscillator genes that may underlie cell-specific differences in clock properties. In addition, we demonstrated that the oscillators of individual cells in the leaf are robust, but become partially desynchronized in constant conditions. Taken together our results suggest that, at the level of individual cells, there are differences in the canonical oscillator mechanism that has been described for plants.