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Competence modifiers synergize with growth factors during mesoderm induction and patterning in Xenopus.
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Tissue culture of Xenopus neurons and muscle cells as a model for studying synaptic induction.
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Identifying the missing links: genes that connect neural induction and primary neurogenesis in vertebrate embryos.
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Hierarchy of events regulating neural crest induction.
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[Molecular mechanisms of the neural induction and morphogenesis].
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Regional biosynthetic markers in the early amphibian embryo.
A search has been made for regional differences in macromolecular synthesis in the axolotl embryo at a stage when the principal regions have become determined but terminal differentiation has not yet begun. The epidermis of the neurula makes a number of abundant proteins which are not made elsewhere. Some of these are identified by immunoprecipitation as cytokeratins (relative molecular masses (Mr) 62,59,54,51 and 46 X 10(3)). At the same stage a network of tonofilaments becomes visible by electron microscopy and is also confined to the epidermis. There is no significant incorporation of 3H-sugars into glycoproteins before neurulation. During neurulation specific species begin to be made by the notochord (Mr 265 and 185 X 10(3)), the mesoderm (315 X 10(3)) and the epidermis (170 X 10(3)). The latter species is water soluble, has a native Mr of 470 X 10(3), is somewhat resistant to trypsin and has a high sugar content. Since these characteristics do not relate to any known glycoprotein it has been given a new name: epimucin. Several neutral glycolipids and gangliosides are present in the early embryo, the most abundant of which is identified as galactocerebroside. Synthesis occurs from fertilization onwards, however even by the neurula stage the qualitative pattern is the same in all parts except for the epidermis which shows two substantial enhancements and one reduction compared to other regions. The differences reported probably relate to physiological functions rather than to the mechanism of determination itself, so their chief importance is as markers of early embryo regions in experiments on induction.
Regionally specific induction by the Spemann-Mangold organizer.
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Neural induction: past, present, and future.
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Molecular dissection of Hox gene induction and maintenance in the hindbrain.
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Experimental embryological methods for analysis of neural induction in the amphibian.
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Inducing embryonic stem cells to differentiate into pancreatic beta cells by a novel three-step approach with activin A and all-trans retinoic acid.
Experimental induction of embryonic stem cells (ESCs) to become pancreatic beta cells can potentially provide ample resource for cell transplantation therapy of type I diabetes mellitus. Most of the previously reported induction strategies were long and complicated, and some required genetic manipulation. Moreover, it has been indicated that the insulin staining of ESC progeny was insulin uptake from the culture medium. Here we show that a simple three-step experimental approach based on the combination induction by activin A, all-trans retinoic acid, and other mature factors is able to induce murine ESCs to differentiate into insulin-producing cells in 2 weeks, and that insulin release of these induced cells is regulated by the glucose concentration. Our insulin-enhanced green fluorescent green protein reporter system excludes the possibility of insulin uptake. Transplantation of these ESC-derived insulin-positive cells can normalize blood glucose levels and rescue the survival of streptozocin-induced diabetic mice. The findings reported here offer a novel in vitro model to study the differentiation mechanism of pancreatic beta cells and a potential source of insulin-producing cells for transplantation therapy of type I diabetes mellitus.
Induction of photoreceptor-specific phenotypes in adult mammalian iris tissue.
We show that iris tissue in the adult rat eye, which is embryonically related to the neural retina, can generate cells expressing differentiated neuronal antigens. In addition, the Crx gene transfer induced the specific antigens for rod photoreceptors in the iris-derived cells, which was not seen in the adult hippocampus-derived neural stem cells. Our findings demonstrate a remarkable plasticity of adult iris tissue with potential clinical applications, as autologous iris tissue can be feasibly obtained with peripheral iridectomy.
Spatially distinct head and heart inducers within the Xenopus organizer region.
BACKGROUND: The mouse anterior visceral endoderm, an extraembryonic tissue, expresses several genes essential for normal development of structures rostral to the anterior limit of the notochord and has been termed the head organizer. This tissue also has heart-inducing activity and expresses mCer1 which, like its Xenopus homolog cerberus, can induce markers of cardiac specification and anterior neural tissue when ectopically expressed. We investigated the relationship between head and heart induction in Xenopus embryos, which lack extraembryonic tissues. RESULTS: We found three regions of gene expression in the Xenopus organizer: deep endoderm, which expressed cerberus; prechordal mesoderm, which showed overlapping but non-identical expression of genes characteristic of the murine head organizer, such as XHex and XANF-1; and leading-edge dorsoanterior endoderm, which expressed both cerberus and a subset of the genes expressed by the prechordal mesoderm. Microsurgical ablation of the cerberus-expressing endoderm decreased the incidence of heart, but not head, formation. Removal of prechordal mesoderm, in contrast, caused deficits of anterior head structures. Finally, although misexpression of cerberus induced ectopic heads, it was unable to induce genes thought to participate in head induction. CONCLUSIONS: In Xenopus, the cerberus-expressing endoderm is required for heart, but not head, inducing activity. Therefore, this tissue is not the topological equivalent of the murine anterior visceral endoderm. We propose that, in Xenopus, cerberus is redundant to other bone morphogenetic protein (BMP) and Wnt antagonists located in prechordal mesoderm for head induction, but may be necessary for heart induction.
Limitation of the size of the vulval primordium of Caenorhabditis elegans by lin-15 expression in surrounding hypodermis.
In the nematode Caenorhabditis elegans six hypodermal cells, the vulval precursor cells, are each competent to generate vulval cells. Normally only the three nearest precursor cells to the uterine anchor cell generate the vulva (22 nuclei), while the three others fuse with the non-specialized hypodermal syncytium (hyp7) surrounding each precursor cell and covering the body. Without an inductive signal from the anchor cell, all six vulval precursor cells fuse with hyp7 and no vulva is formed. But without activity of the vulval determination gene lin-15(+), all six cells undergo vulval divisions whether the anchor cell is present or not. Using mosaic analysis, we demonstrate here that lin-15(+) expression is necessary in cells other than the vulval precursor cells or the anchor cell, most probably in the hyp7 syncytium. We propose that lin-15(+) is active in hyp7 in order to repress an intrinsic vulval program in the precursor cells. The inductive signal from the anchor cell counteracts this repression for three precursor cells, allowing them to generate vulval cells. Such a two-signal (repressor/derepressor) mechanism may operate in other cases of tissue induction.