Noto Personal Organizer is a mini application or 'window gadget' that you can move around your computer desktop. It is very easy to use because it works exactly like a real personal organizer, with page turning and separate side tabbed sections, such as: day to view, week to view, month to view, projects section, info section and address book. It also has added benefits such as a selection bars and icons that can be dragged and dropped within Noto to highlight certain events. Alarms can be set so you don't miss important appointments. There are also embedded gadgets, including a calculator, mp3 player and a memory game. Noto is customizable with a pre-loaded selection of cover designs, icons, gadget designs, and maps. You can add more to your selection by connecting online from within Noto to drag and drop more content from our download section. For example, you can have a Van Gogh cover design, a London underground map, a red mp3 player, and a scuba diving icon for your calendar.
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Noto Personal Organizer works exactly like a real personal organizer, with page turning and separate side tabbed sections. This includes a week to view, month to view and projects section. Of course, you've also got an address book and you can set alarms to be triggered when an important event has come up. In addition Noto Personal Organizer gives you a host of other tools including a calculator, mp3 player and a memory game.
The notochord has organizer properties and is required for floor plate induction and dorsoventral patterning of the neural tube. This activity has been attributed to sonic hedgehog (shh) signaling, which originates in the notochord, forms a gradient, and autoinduces shh expression in the floor plate. However, reported data are inconsistent and the spatiotemporal development of the relevant shh expression domains has not been studied in detail. We therefore studied the expression dynamics of shh in rabbit, chicken and Xenopus laevis embryos (as well as indian hedgehog and desert hedgehog as possible alternative functional candidates in the chicken).
The initial dorsoventral patterning of the neural tube exemplifies a classical induction from neighboring tissue. As inductive interactions belong to central concepts in developmental biology [76], the early role of the notochord serves as a paradigmatic example of induction by organizers, which are defined by their ability to induce and pattern adjacent tissue [3]. Early studies in amphibian embryos suggested that the notochord is required for correct morphological dorsoventral patterning of the neural tube [37], while other observations indicated, however, that a more cautious interpretation is needed [38, 75]. Similarly, the notochord in the chick was shown to be required for floor plate development as well for its specific inductive function [59, 90]. For example, implantation of the notochord lateral to the neural tube causes ventralization of the lateral tube wall and formation of ectopic floor plate, as seen by cell shape change or ectopic axon outgrowth [59, 91].
Shh has been shown to be strongly expressed both in the notochord and in the floor plate of different organisms and to have the ability to induce a floor plate when expressed ectopically [18, 31, 65]. Importantly, an isolated shh-expressing floor plate forms a gradient of shh within the neural tube and is also able to induce a ventral fate in the adjacent neural tissue [60], which indicates that the floor plate also has organizer activity [3]. Therefore, the role of the notochord may be related to expression and secretion of shh, which induces its own expression in prospective floor plate cells. According to this hypothesis, shh expression in the notochord must precede its expression in the floor plate and, indeed, this has been unambiguously shown in mouse [10, 18] and rat [65] embryos. It has been suggested that the six progenitor domains responsible for dorsoventral differences in the ventral neural tube are induced even prior to shh expression in the floor plate [64] and, therefore, if the shh gradient is causally involved in this induction, the notochord must be the primary source of the gradient.
In X. laevis, shh expression starts at early gastrula stage with a sickle-shaped domain in the area above the dorsal blastopore (Fig. 5a). During gastrulation, this domain undergoes narrowing and elongation along the AP axis (Fig. 5b, c). Technovit sections reveal an early gastrula expression domain in the deep layer of the dorsal marginal zone, with expression absent from the dorsal lip and superficial mesoderm (Fig. 6a). The early shh domain corresponds to the area that is known to give rise to the axial mesoderm and is adjacent to the prospective neuroectoderm. At mid-gastrula, expression is confined to the deep involuted layer (Fig. 6b), and at the end of gastrulation, shh expression extends along the dorsal midline (Fig. 5d). Surprisingly, the sections reveal expression in the inner layer of the midline ectoderm and in the midline mesoderm (Fig. 6b, c). The width of the expression in both domains follows differences seen already in whole-mount views with a narrow posterior and wide anterior domain. During neurulation, shh expression undergoes further elongation and narrowing (Fig. 5e). Sections at stage 14 reveal expression in the inner neuroectoderm layer and weak expression in the rod-like notochord. In the anterior neuroectoderm, strong and wide expression is present in both inner cells, which display columnar morphology and in flat outer ectoderm cells. Midline mesoderm, which at this level forms a plate, also displays a strong scattered expression in epithelial-like cells. At the more anterior level (prospective superficial), expression of shh is present in the mesoderm, but excluded from the overlying ectoderm. At early tailbud stage (Figs. 5f, 6h), shh expression is confined to the floor plate, notochord, hypochord and at the level of the posterior notochord to the archenteron roof. In addition, we found that patched 2 expression is specifically activated in the midline at mid-gastrula stages, suggesting activated hedgehog signaling already at this stage (Fig. 5g). Summarizing, neuroectodermal expression of shh is initiated at late gastrula/early neurula stages, whereas the mesodermal expression is initiated at early gastrula in the dorsal organizer area.
On the basis of the results presented here, we hypothesize that divergent induction of shh expression in the midline neuroectoderm is due to divergent topography and morphogenetic movements during gastrulation. Evolution of vertebrate gastrulation has been proposed to be driven by increasing of yolk mass [5], which may lead via premature posterior activation of PCP pathway to stepwise transformation of circular blastopore into straight primitive streak of amniotes [7, 78, 80, 93]. This modified topography of organizer in turn may affect mechanisms of notochord formation. In the chick (Fig. 7), the notochord is laid down during so-called node (or primitive streak) regression [77], a process that is accompanied by a shift of the relative node position to the posterior pole of the embryo. Just prior to regression, the node tissue undergoes counterclockwise rotation [15, 27]. This rotation breaks the symmetry of the horseshoe-like shh domain located anterior to the node and transforms it into left-sided [15, 27, 39]. We propose that the notochord progenitor domain, which is located in the middle of the node [70] and at this stage does not express shh [86], is shifted to the right side (see Fig. 7). During primitive streak regression, tissues lateral to the node are shifted posteriorly, whereas the prospective neural plate undergoes elongation [68]. Therefore, the ectodermal shh domain also undergoes elongation which creates a stripe-like shh expression domain in the future floor plate (cf. Additional file 3: Fig. 3) which persists during studied stages and makes the inductive influence from the notochord unnecessary.
In the mouse and in the rabbit, however (Fig. 8), notochord formation is not accompanied by noticeable node regression [33, 96]. The major part of the murine notochord seems to be formed by convergent extension of the cells deriving from shh-positive node tissue. Whether the posterior part of the floor plate is also derived from the node is still a matter of debate. During notochord formation, the node remains symmetrical and bears symmetrical shh domain [25]. The axial mesoderm is shh positive along its whole length. The neural plate extension occurs by growth of tissue distant to the organizer [92]. Therefore, the induction of the floor plate requires external inductive stimuli, which are enabled by growth of the notochord beneath the prospective floor plate tissue (cf. Figure 8).
It has been suggested that the hedgehog family arose from single hedgehog gene also found in basal chordate amphioxus [72], whereas the Ciona intestinalis possesses two members (Ci-hh1 and Ci-hh2) that emerged in independent duplication events [84]. Analysis of hedgehog expression in Ciona shows expression of Ci-hh2 in the ventral cells of the neural tube tissue prior to its expression in the notochord [84]. Initial shh expression in the ventral neural tube may be related to invariant development of cell lineage and early axis determination in ascidian embryogenesis, which functionally have lost organizer tissue although some inductive interaction and even regulative capacities have been observed [6, 47, 82, 83]. However, in amphioxus with its highly regulative development [87, 88] this dynamics may display an inverse spatiotemporal relation: although only whole-mount views from early stages were shown, the authors suggest that initially the hedgehog expression is localized in the presumptive endoderm and the notochord [72]. The situation in amphioxus may represent ancestral mode of floor plate induction. 2ff7e9595c
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