Boundaries and Functional Domains in the Animal/Vegetal Axis of Xenopus Gastrula Mesoderm

AbstractPatterning of the Xenopus gastrula marginal zone in the axis running equatorially from the Spemann organizer—the so-called “dorsal/ventral axis”—has been extensively studied. It is now evident that patterning in the animal/vegetal axis also needs to be taken into consideration. We have shown that an animal/vegetal pattern is apparent in the marginal zone by midgastrulation in the polarized expression domains of Xenopusbrachyury (Xbra) and Xenopusnodal-related factor 2 (Xnr2). In this report, we have followed cells expressing Xbra in the presumptive trunk and tail at the gastrula stage, and find that they fate to presumptive somite, but not to ventrolateral mesoderm of the tailbud embryo. From this, we speculate that the boundary between the Xbra- and Xnr2-expressing cells at gastrula corresponds to a future tissue boundary. In further experiments, we show that the level of mitogen-activated protein kinase (MAPK) activation is polarized along the animal/vegetal axis, with the Xnr2-expressing cells in the vegetal marginal zone having no detectable activated MAPK. We show that inhibition of MAPK activation in Xenopus animal caps results in the conversion of Xnr2 from a dorsal mesoderm inducer to a ventral mesoderm inducer, supporting a role for Xnr2 in induction of ventral mesoderm

カリフォルニア ダイガク オナー プログラム チョウサ リョコウ

We visited four campuses of the University of California to know the details of honors programs being run by individual campuses. Our fact-finding visit included the following mandates: first, meeting with the program coordinators and teachers; second, collecting information/files/documents relevant to honors program at each campus; third, interviewing honor students, and finally class observation of the programs. We spend half-day to whole day on each campus and hereby we report the summaries of our fact-finding site-visit. While we were on the trip trying to see more people and collect more information relevant to honors program, we at the same time started having an understanding that, besides the details of the programs now running, it would be more meaningful and significant to know the history of the programs in the social context, and how the quality of the programs is maintained organizationally. Our most important discovery is that the high spirit of the faculty members, coordinators and administrative officers is the driving force for honors program at University of California. We do not think it totally possible to “import” honors program from California. It would rather be out mission to “create” Japanese-adaptation of honors program that fully incorporates the social background of Japan

Wnt5 is required for notochord cell intercalation in the ascidian Halocynthia roretzi

Background information. In the embryos of various animals, the body elongates after gastrulation by morphogenetic movements involving convergent extension. The Wnt/PCP (planar cell polarity) pathway plays roles in this process, particularly mediolateral polarization and intercalation of the embryonic cells. In ascidians, several factors in this pathway, including Wnt5, have been identified and found to be involved in the intercalation process of notochord cells

Branching pattern and morphogenesis of medusa tentacles in the jellyfish Cladonema pacificum (Hydrozoa, Cnidaria)

Abstract Background Branched structures are found in many natural settings, and the molecular and cellular mechanisms underlying their formation in animal development have extensively studied in recent years. Despite their importance and the accumulated knowledge from studies on several organs of Drosophila and mammals, much remains unknown about branching mechanisms in other animal species. We chose to study the jellyfish species Cladonema pacificum. Unlike many other jellyfish, this species has branched medusa tentacles, and its basal phylogenetic position in animal evolution makes it an ideal organism for studying and understanding branching morphogenesis more broadly. Branched tentacles are unique compared to other well-studied branched structures in that they have two functionally distinct identities: one with adhesive organs for attaching to a substratum, and another with nematocyst clusters for capturing prey. Results We began our analyses on C. pacificum tentacles by observing their branching during growth. We found that tentacle branches form through repeated addition of new branches to the proximal region of the main tentacle while it is elongating. At the site of branch bud formation, we observed apical thickening of the epidermal epithelial layer, possibly caused by extension of the epithelial cells along the apico-basal axis. Interestingly, tentacle branch formation required receptor tyrosine kinase signaling, which is an essential factor for branching morphogenesis in Drosophila and mammals. We also found that new branches form adhesive organs first, and then are transformed into branches with nematocyst clusters as they develop. Conclusions These results highlight unique features in branch generation in C. pacificum medusa tentacles and illuminate conserved and fundamental mechanisms by which branched structures are created across a variety of animal species

Regulation of the Number of Cell Division Rounds by Tissue-Specific Transcription Factors and Cdk Inhibitor during Ascidian Embryogenesis

<div><p>Mechanisms that regulate the number of cell division rounds during embryogenesis have remained largely elusive. To investigate this issue, we used the ascidian, which develops into a tadpole larva with a small number of cells. The embryonic cells divide 11.45 times on average from fertilization to hatching. The number of cell division rounds varies depending on embryonic lineages. Notochord and muscle consist of large postmitotic cells and stop dividing early in developing embryos. Here we show that conversion of mesenchyme to muscle cell fates by inhibition of inductive FGF signaling or mis-expression of a muscle-specific key transcription factor for muscle differentiation, Tbx6, changed the number of cell divisions in accordance with the altered fate. Tbx6 likely activates a putative mechanism to halt cell division at a specific stage. However, precocious expression of Tbx6 has no effect on progression of the developmental clock itself. Zygotic expression of a <i>cyclin-dependent kinase inhibitor, CKI-b</i>, is initiated in muscle and then in notochord precursors. CKI-b is possibly downstream of tissue-specific key transcription factors of notochord and muscle. In the two distinct muscle lineages, postmitotic muscle cells are generated after 9 and 8 rounds of cell division depending on lineage, but the final cell divisions occur at a similar developmental stage. <i>CKI-b</i> gene expression starts simultaneously in both muscle lineages at the 110-cell stage, suggesting that CKI-b protein accumulation halts cell division at a similar stage. The difference in the number of cell divisions would be due to the cumulative difference in cell cycle length. These results suggest that muscle cells do not count the number of cell division rounds, and that accumulation of CKI-b protein triggered by tissue-specific key transcription factors after cell fate determination might act as a kind of timer that measures elapsed time before cell division termination.</p></div

Numbers of cell divisions of mesenchyme cells in Tbx6-mis-expressing embryos.

<p>B7.3 and B7.7 mesenchyme blastomeres were isolated from 64-cell embryos that had been injected with control <i>H2B:mCherry</i> mRNA (gray bars) and <i>Tbx6</i> mRNA (green bars). The numbers of descendant cells were counted, and the numbers of cell divisions were then calculated. On the abscissa, e.g., 3 cell divisions represents partial embryos that divided 2.50 to 3.49 times. Numbers of partial embryos observed are indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090188#pone-0090188-g002" target="_blank">Fig. 2B</a>. Proportions of major specimens are given above the columns.</p

<i>CKI-b</i> gene expression.

<p>(A) (upper row) <i>In situ</i> hybridization with the <i>Hr-CKI-b</i> probe. The expression becomes evident at the 110-cell stage in the B7.4 and B7.8 muscle lineage precursors simultaneously. At the 110-cell stage plus one hour, there are 4 B7.4 descendants and 2 B7.8 descendants. At 2 hours after the 110-cell stage, the expression has become evident in notochord precursors. The stages from the 110-cell stage through the gastrula and up to the neural plate stage are shown. (bottom) Expression of <i>CKI-b</i> in embryos whose cleavages were arrested at the 110-cell stage. Asterisks indicate <i>de novo</i> expression at the 110-cell stage plus 4 hours, which probably corresponds to the heavily stained cells in the above photo. (B) Schematic representation of the arrested 110-cell embryos, showing the position of each tissue precursor cell. Vegetal view. (C) Timetable of <i>CKI-b</i> expression and cell division progression after the 64-cell stage. Mus, muscle. Not, notochord.</p

Expression of <i>CKI-b</i> occurs downstream of inductive cell interaction and the key transcription factor.

<p>(A) Schematic representation of arrested 110-cell embryos, showing the position of each tissue precursor cell. Vegetal view. (B) <i>CKI-b</i> expression in a cleavage-arrested 110-cell embryo treated with DMSO as a control. (C) That treated with MEK inhibitor. Expression in the notochord was lost, and ectopic expression was evident in mesenchyme cells. (D) <i>CKI-b</i> expression in a cleavage-arrested 110-cell embryo injected with control MO. (E) That in an embryo injected with Brachyury MO. The expression in notochord cells was lost. Numbers of embryos that showed the expression in each tissue per those of observed embryos are shown. Mch, mesenchyme. Mus, muscle. Not, notochord.</p