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Stable integration of cloned gene products into the Xenopus genome is necessary to control the time and place of expression, to express genes at later stages of embryonic development, and to define how enhancers and promoters regulate gene expression within the embryo. The protocol demonstrated here can be used to efficiently produce transgenic Xenopus laevis embryos. This transgenesis approach involves three parts: 1. Sperm nuclei are isolated from adult X. laevis testis by treatment with lysolecithin, which permeabilizes the sperm plasma membrane. 2. Egg extract is prepared by low speed centrifugation, addition of calcium to cause the extract to progress to interphase of the cell cycle, and a high-speed centrifugation to isolate interphase cytosol. 3. Nuclear transplantation: the nuclei and extract are combined with the linearized plasmid DNA to be introduced as the transgene and a small amount of restriction enzyme. During a short reaction, egg extract partially decondenses the sperm chromatin and the restriction enzyme generates chromosomal breaks that promote recombination of the transgene into the genome. The treated sperm nuclei are then transplanted into unfertilized eggs. Integration of the transgene usually occurs prior to the first embryonic cleavage such that the resulting embryos are not chimeric. These embryos can be analyzed without any need to breed to the next generation, allowing for efficient and rapid generation of transgenic embryos for analyses of promoter and gene function. Adult X. laevis resulting from this procedure also propagate the transgene through the germline and can be used to generate lines of transgenic animals for multiple purposes.

Frog Genome The African clawed frog Xenopus tropicalis is the first amphibian to have its genome sequenced. Hellsten et al. (p. 633 , see the cover) present an analysis of a draft assembly of the genome. The genome of the frog, which is an important model system for developmental biology, encodes over 20,000 protein-coding genes, of which more than 1700 genes have identified human disease associations. Detailed comparison of the content of protein-coding genes with other tetrapods—human and chicken—reveals extensive shared synteny, occasionally spanning entire chromosomes.

Fibroblast growth factor (FGF) signalling plays a major role during early vertebrate development. It is involved in the specification of the mesoderm, control of morphogenetic movements, patterning of the anterior-posterior axis, and neural induction. In mammals, 22 FGF ligands have been identified, which can be grouped into seven subfamilies according to their sequence homology and function. We have cloned 17 fgf genes from Xenopus tropicalis and have analysed their temporal expression by RT-PCR and spatial expression by whole mount in situ hybridisation at key developmental stages. It reveals the diverse expression pattern of fgf genes during early embryonic development. Furthermore, our analysis shows the transient nature of expression of several fgfs in a number of embryonic tissues. This study constitutes the most comprehensive description of the temporal and spatial expression pattern of fgf ligands and receptors during vertebrate development to date. Developmental Dynamics 238:1467-1479, 2009. (c) 2009 Wiley-Liss, Inc.

The molecular mechanisms that underlie the development of primitive myeloid cells in vertebrate embryos are not well understood. Here we characterize the role of cebpa during primitive myeloid cell development in Xenopus. We show that cebpa is one of the first known hematopoietic genes expressed in the embryo. Loss- and gain-of-function studies show that it is both necessary and sufficient for the development of functional myeloid cells. In addition, we show that cebpa misexpression leads to the precocious induction of myeloid cell markers in pluripotent prospective ectodermal cells, without the cells transitioning through a general mesodermal state. Finally, we use live imaging to show that cebpa-expressing cells exhibit many attributes of terminally differentiated myeloid cells, such as highly active migratory behavior, the ability to quickly and efficiently migrate toward wounds and phagocytose bacteria, and the ability to enter the circulation. Thus, C/EPBα is the first known single factor capable of initiating an entire myelopoiesis pathway in pluripotent cells in the embryo.

Peptide growth factors may play a role in patterning of the early embryo, particularly in the induction of mesoderm. We have explored the role of fibroblast growth factor (FGF) in early Xenopus development by expressing a dominant negative mutant form of the FGF receptor. Using a functional assay in frog oocytes, we found that a truncated form of the receptor effectively abolished wild-type receptor function. Explants from embryos expressing this dominant negative mutant failed to induce mesoderm in response to FGF. In whole embryos the mutant receptor caused specific defects in gastrulation and in posterior development, and overexpression of a wild-type receptor could rescue these developmental defects. These results demonstrate that the FGF signaling pathway plays an important role in early embryogenesis, particularly in the formation of the posterior and lateral mesoderm.

The amphibian embryo has classically been one of the best systems for elucidating the molecular mechanisms of early development, in particular for studies of mesodermal and neural induction. Amphibian embryos develop externally and are large and robust. Therefore, tissues can be dissected, isolated, or transplanted with high precision and ease in these embryos. In addition, it is relatively easy to manipulate the expression of gene products by injecting in-vitro transcribed RNAs into developing embryos. However, since RNAs are translated soon after injection, this method has been used mainly for studying early stages of development. Manipulating genes specifically during later stages of development requires fine control over the time and place of expression, which can be achieved only through transgenic technology. In this chapter, we describe a very efficient method of transgenesis developed for Xenopus laevis and Xenopus tropicalis. 1.2. Background Understanding the molecular basis of pattern formation and differentiation in frog embryos was previously hindered by the lack of a system for temporal and tissue-specific expression of wild-type and mutant forms of developmentally important genes. RNA injection, the most common transient expression method in Xenopus, has been effectively used to study maternally expressed genes. However, since RNAs are translated immediately after injection, this method is unfavorable for the study of zygotic gene products that are expressed only after the midblastula transition. Direct injection of DNA can be used to express genes behind temporal and tissue-specific promoters after the midblastula transition.

O tromboembolismo pulmonar (TEP) é uma importante causa de morbimortalidade nos pacientes submetidos a procedimentos neurocirúrgicos. O objetivo deste estudo foi apresentar um caso de trombólise intra-arterial pulmonar em pós-operatório recente de neurocirurgia. Paciente do sexo masculino, sendo submetido a clipagem de aneurisma de artéria comunicante anterior, apresentou como complicação no sétimo dia de pós-operatório, tromboembolismo pulmonar maciço, apresentando instabilidade hemodinâmica, sendo optado pela trombólise intra-arterial pulmonar com alteplase. Apresentou evolução satisfatória, sem complicações hemorrágicas, recebendo alta hospitalar. O tromboembolismo pulmonar é uma condição com alta morbi-mortalidade no pós-operatório de neurocirurgia, devendo ser a trombólise ser uma alternativa terapêutica nos casos refratários ao tratamento clínico. Pulmonary thromboembolism is a major cause of morbidity and mortality of patients undergoing neurosurgical procedures. The purpose of this study was to present a case of intra-arterial pulmonary thrombolysis in recent neurosurgery postoperative period. Male patient, undergoing neurosurgery, presented as a complication on the seventh day of postoperative massive pulmonary embolism with hemodynamic instability and intraarterial pulmonary thrombolysis with alteplase was indicated. Evolution was satisfactory without bleeding complications and patient was discharged. Pulmonary thromboembolism is a high morbidity and mortality condition at neurosurgical postoperative period and thrombolysis should be an alternative therapy in cases refractory to clinical treatment.

Pulmonary thromboembolism is a major cause of morbidity and mortality of patients undergoing neurosurgical procedures. The purpose of this study was to present a case of intra-arterial pulmonary thrombolysis in recent neurosurgery postoperative period. Male patient, undergoing neurosurgery, presented as a complication on the seventh day of postoperative massive pulmonary embolism with hemodynamic instability and intraarterial pulmonary thrombolysis with alteplase was indicated. Evolution was satisfactory without bleeding complications and patient was discharged. Pulmonary thromboembolism is a high morbidity and mortality condition at neurosurgical postoperative period and thrombolysis should be an alternative therapy in cases refractory to clinical treatment.

Vertebrate blood formation occurs in 2 spatially and temporally distinct waves, so-called primitive and definitive hematopoiesis. Although definitive hematopoiesis has been extensively studied, the development of primitive myeloid blood has received far less attention. In Xenopus, primitive myeloid cells originate in the anterior ventral blood islands, the equivalent of the mammalian yolk sac, and migrate out to colonize the embryo. Using fluorescence time-lapse video microscopy, we recorded the migratory behavior of primitive myeloid cells from their birth. We show that these cells are the first blood cells to differentiate in the embryo and that they are efficiently recruited to embryonic wounds, well before the establishment of a functional vasculature. Furthermore, we isolated spib, an ETS transcription factor, specifically expressed in primitive myeloid precursors. Using spib antisense morpholino knockdown experiments, we show that spib is required for myeloid specification, and, in its absence, primitive myeloid cells retain hemangioblast-like characteristics and fail to migrate. Thus, we conclude that spib sits at the top of the known genetic hierarchy that leads to the specification of primitive myeloid cells in amphibians.

Pulmonary thromboembolism is a major cause of morbidity and mortality of patients undergoing neurosurgical procedures. The purpose of this study was to present a case of intra-arterial pulmonary thrombolysis in recent neurosurgery postoperative period. Male patient, undergoing neurosurgery, presented as a complication on the seventh day of postoperative massive pulmonary embolism with hemodynamic instability and intraarterial pulmonary thrombolysis with alteplase was indicated. Evolution was satisfactory without bleeding complications and patient was discharged. Pulmonary thromboembolism is a high morbidity and mortality condition at neurosurgical postoperative period and thrombolysis should be an alternative therapy in cases refractory to clinical treatment.

JUSTIFICATIVA E OBJETIVOS: O Transfusion-Related Acute Lung Injury (TRALI), é definido como um edema pulmonar não cardiogênico, relacionado à transfusão de sangue ou derivados, evoluindo com necessidade de ventilação mecânica na grande maioria dos casos. O objetivo deste estudo foi apresentar um caso de TRALI em pós-operatório imediato de neurocirurgia. RELATO DO CASO: Paciente do sexo masculino, 69 anos, sem comprometimento pulmonar prévio, foi submetido à ressecção cirúrgica de glioblastoma multiforme, apresentando complicações intra-operatórias (broncoespasmo e diminuição da saturação de oxigênio), após ter recebido plasma fresco congelado, sendo diagnosticado TRALI. O paciente foi mantido sedado, sob ventilação mecânica e monitorização hemodinâmica invasiva, com melhora progressiva do quadro, recebendo alta da unidade de terapia intensiva (UTI) no 8º dia de pós-operatório. CONCLUSÕES: O TRALI deve ser investigado nos pacientes que recebem hemoderivados e apresentam alterações pulmonares. BACKGROUND AND OBJECTIVES: The Transfusion-Related Acute Lung Injury (TRALI), is defined as noncardiogenic pulmonary edema temporally related to transfusion therapy, evolving with ventilation necessity mechanics in the great majority of the cases. This objective of this study was to present case of TRALI in the immediate postoperative of neurosurgery. CASE REPORT: We describe the case of a patient who presented broncoespasm and decreased oxygen saturation after to have received fresh-frozen plasma in the neurosurgery, who presented TRALI. The patient was submitted a invasive hemodynamic monitoring, sedation and supplemental oxygen with mechanical ventilation, with gradual improvement, leaving the intensive care unit in the eight day of postoperative. CONCLUSIONS: The TRALI must be investigated in the patients who receive transfusion therapy and present lung injury.

The Transfusion-Related Acute Lung Injury (TRALI), is defined as noncardiogenic pulmonary edema temporally related to transfusion therapy, evolving with ventilation necessity mechanics in the great majority of the cases. This objective of this study was to present case of TRALI in the immediate postoperative of neurosurgery.We describe the case of a patient who presented broncoespasm and decreased oxygen saturation after to have received fresh-frozen plasma in the neurosurgery, who presented TRALI. The patient was submitted a invasive hemodynamic monitoring, sedation and supplemental oxygen with mechanical ventilation, with gradual improvement, leaving the intensive care unit in the eight day of postoperative.The TRALI must be investigated in the patients who receive transfusion therapy and present lung injury.

In this issue of Blood, Myers and Krieg present an elegant series of experiments, which suggest that the hemangioblast may be a state of competence rather than a bipotential progenitor state that exists in vivo.

The formation of mesoderm is an important developmental process of vertebrate embryos, which can be broken down into several steps; mesoderm induction, patterning, morphogenesis and differentiation. Although mesoderm formation in Xenopus has been intensively studied, much remains to be learned about the molecular events responsible for each of these steps. Furthermore, the interplay between mesoderm induction, patterning and morphogenesis remains obscure. Here, we describe an enhanced functional screen in Xenopus designed for large-scale identification of genes controlling mesoderm formation. In order to improve the efficiency of the screen, we used a Xenopus tropicalis unique set of cDNAs, highly enriched in full-length clones. The screening strategy incorporates two mesodermal markers, Xbra and Xmyf-5, to assay for cell fate specification and patterning, respectively. In addition we looked for phenotypes that would suggest effects in morphogenesis, such as gastrulation defects and shortened anterior–posterior axis. Out of 1728 full-length clones we isolated 82 for their ability to alter the phenotype of tadpoles and/or the expression of Xbra and Xmyf-5. Many of the clones gave rise to similar misexpression phenotypes (synphenotypes) and many of the genes within each synphenotype group appeared to be involved in similar pathways. We determined the expression pattern of the 82 genes and found that most of the genes were regionalized and expressed in mesoderm. We expect that many of the genes identified in this screen will be important in mesoderm formation.

The endoderm gives rise the respiratory and digestive tract epithelia as well as associated organs such as the liver, lungs and pancreas. Investigations examining the molecular basis of embryonic endodermal patterning and organogenesis have been hampered by the lack of regionally expressed molecular markers in the early endoderm. By differentially screening an arrayed cDNA library, combined with an in situ hybridization screen we identified 13 new genes regionally expressed in the early tailbud endoderm of the Xenopus embryo. The putative proteins encoded by these cDNAs include a cell surface transporter, secreted proteins, a protease, a protease inhibitor, an RNA-binding protein, a phosphatase inhibitor and several enzymes. We find that the expression of these genes falls into one of three re-occurring domains in the tailbud embryo; (1). a ventral midgut, (2). posterior to the midgut and (3). in the dorsal endoderm beneath the notochord. Several of these genes are also regionally expressed at gastrula and neurula stages and appear to mark territories that were previously only predicted by the endoderm fate map. This indicates that there is significant positional identity in the early endoderm long before stages 28-32 when regional specification of the endoderm is thought to occur. These new genes provide valuable tools for studying endodermal patterning and organogenesis in Xenopus.

The mechanisms that establish behavioral, cognitive, and neuroanatomical asymmetries are poorly understood. In this study, we analyze the events that regulate development of asymmetric nuclei in the dorsal forebrain. The unilateral parapineal organ has a bilateral origin, and some parapineal precursors migrate across the midline to form this left-sided nucleus. The parapineal subsequently innervates the left habenula, which derives from ventral epithalamic cells adjacent to the parapineal precursors. Ablation of cells in the left ventral epithalamus can reverse laterality in wild-type embryos and impose the direction of CNS asymmetry in embryos in which laterality is usually randomized. Unilateral modulation of Nodal activity by Lefty1 can also impose the direction of CNS laterality in embryos with bilateral expression of Nodal pathway genes. From these data, we propose that laterality is determined by a competitive interaction between the left and right epithalamus and that Nodal signaling biases the outcome of this competition.

The transgenic technique in Xenopus allows one to misexpress genes in a temporally and spatially controlled manner. However, this system suffers from two experimental limitations. First, the restriction enzyme-mediated integration procedure relies on chromosomal damage, resulting in a percentage of embryos failing to develop normally. Second, every transgenic embryo has unique sites of integration and unique transgene copy number, resulting in variable transgene expression levels and variable phenotypes. For these reasons, we have adapted the Gal4-UAS method for targeted gene expression to Xenopus . This technique relies on the generation of transgenic lines that carry “activator” or “effector” constructs. Activator lines express the yeast transcription factor, Gal4, under the control of a desired promoter, whereas effector lines contain DNA-binding motifs for Gal4-(UAS) linked to the gene of interest. We show that on intercrossing of these lines, the effector gene is transcribed in the temporal and spatial manner of the activator's promoter. Furthermore, we use the Gal4-UAS system to misexpress Xvent-2, a transcriptional target of bone morphogenetic protein 4 (BMP4) signaling during early embryogenesis. Embryos inheriting both the Gal4 activator and Xvent-2 effector transgenes display a consistent microcephalic phenotype. Finally, we exploit this system to characterize the neural and mesodermal defects obtained from early misexpression of Xvent-2. These results emphasize the potential of this system for the controlled analyses of gene function in Xenopus .

Signal transduction through the FGF receptor is essential for the specification of the vertebrate body plan. Blocking the FGF pathway in early Xenopus embryos inhibits mesoderm induction and results in truncation of the anterior–posterior axis. The Drosophilagene sprouty encodes an antagonist of FGF signaling, which is transcriptionally induced by the pathway, but whose molecular functions are poorly characterized. We have cloned Xenopus sprouty2 and show that it is expressed in a similar pattern to known FGFs and is dependent on the FGF/Ras/MAPK pathway for its expression. Overexpression of Xsprouty2 in both embryos and explant assays results in the inhibition of the cell movements of convergent extension. Although blocking FGF/Ras/MAPK signaling leads to an inhibition of mesodermal gene expression, these markers are unaffected by Xsprouty2, indicating that mesoderm induction and patterning occurs normally in these embryos. Finally, using Xenopus oocytes we show that Xsprouty2 is an intracellular antagonist of FGF-dependent calcium signaling. These results provide evidence for at least two distinct FGF-dependent signal transduction pathways: a Sprouty-insensitive Ras/MAPK pathway required for the transcription of most mesodermal genes, and a Sprouty-sensitive pathway required for coordination of cellular morphogenesis.

Summary: Morpholino (MO) based inhibition of translational initiation represents an attractive methodology to eliminate gene function during Xenopus development (Heasman et al., 2000). However, the degree to which a given target protein can be eliminated and the longevity of this effect during embryogenesis has not been documented. To examine the efficacy of MOs, we have used transgenic Xenopus lines that harbour known numbers of integrations of a GFP reporter under the control of the ubiquitous and highly expressed CMV promoter (Fig. 1a). In addition we have investigated the longevity of the inhibitory effect by using transgenic lines expressing GFP specifically in the lens of tadpoles. These transgenic lines represent the ideal control for the technique as the promoters are highly expressed and GFP can be easily detected by fluorescence and immunoblotting. Moreover, as GFP has no function in development, the levels of inhibition can be tested in an otherwise normal individual. Here we report that MOs are able to efficiently and specifically inhibit the translation of GFP in transgenic lines from Xenopus laevis and Xenopus tropicalis and the inhibitory effect is long-lived, lasting into the tadpole stages. genesis 30:110–113, 2001. © 2001 Wiley-Liss, Inc.

Multicellular organisms coordinate their growth, development and homeostasis through cell-cell communication mediated by a relatively small number of extracellular signaling molecules, often referred to as growth factors. Nowadays, it is difficult to open a new volume of a developmental biology

The two mainreasons for this are that the embryosdevelop externally and their relativelylarge size allows embryologists toperform microsurgery and manipu-late the embryos experimentally inways that are not as easy in other ver-tebrate embryos (e.g. mouse or zebra-fish). Most of the early experimentswere done on embryos from

Background and Purpose The incidence of cerebellar infarction in a series of patients with stroke is approximately 1.5%. The average patient age in most reported series is 62 years. The most common etiologies in this age group are atherosclerosis and cardiac embolism. The aim of this study was to determine the causes and mechanisms of cerebellar infarction in patients younger than 40 years. Methods We analyzed retrospectively the clinical and radiological data from 21 men and 16 women with cerebellar infarction admitted to our hospital from January 1986 to December 1996. The patients had been studied extensively to determine the etiology of the cerebellar infarction. Results In the 37 patients (mean age, 30 years), 29 infarcts were limited to one territory (15 in the posteroinferior cerebellar artery [PICA]; 14 in the superior cerebellar artery); 8 had nonterritorial infarctions. The most common stroke mechanisms in each territory were as follows: PICA: nonatherosclerotic vasculopathic (67%), cardioembolic (20%), and hematologic and cryptogenic (each 7%); superior cerebellar artery: cardioembolic (42%), cryptogenic (31%), migrainous (21%), and nonatherosclerotic vasculopathic and hematologic (each 7%); and mixed territory: nonatherosclerotic vasculopathic (50%), cryptogenic (25%), cardioembolic (12%), and hematologic (12%). Conclusions The most common mechanism of cerebellar infarctions was arterial occlusion as a result of intracranial vertebral artery dissection (40%), mainly with PICA involvement. Embolism from a cardiac source resulted primarily from patent foramen ovale and rheumatic valvular disease. Hematologic disturbances and migraine were responsible for a few cases.

Summary Embryonic wound healing provides a perfect example of efficient recovery of tissue integrity and homeostasis, which is vital for survival. Tissue movement in embryonic wound healing requires two functionally distinct actin structures: a contractile actomyosin cable and actin protrusions at the leading edge. Here, we report that the discrete formation and function of these two structures is achieved by the temporal segregation of two intracellular upstream signals and distinct downstream targets. The sequential activation of ERK and phosphoinositide 3-kinase (PI3K) signalling divides Xenopus embryonic wound healing into two phases. In the first phase, activated ERK suppresses PI3K activity, and is responsible for the activation of Rho and myosin-2, which drives actomyosin cable formation and constriction. The second phase is dominated by restored PI3K signalling, which enhances Rac and Cdc42 activity, leading to the formation of actin protrusions that drive migration and zippering. These findings reveal a new mechanism for coordinating different modes of actin-based motility in a complex tissue setting, namely embryonic wound healing.

The first extracellular domain of the cadherins has been shown to exhibit extensive sequence homology with the amino termini of the HA1 chains of influenza strain A hemagglutinins. These regions of homology are known to be functionally important in both the cadherins and the hemagglutinins. The homologous regions harbor the tripeptide HAV, which has been identified as being the cadherin cell adhesion recognition sequence. Here we report that members of the rapidly expanding family of fibroblast growth factor receptors also possess HAV-containing regions. These regions are homologous to the HAV-containing regions present within both the hemagglutinins and the cadherins and appear to be involved in regulating the function of the fibroblast growth factor receptors. We speculate that the HAV motif may represent an evolutionarily conserved amino acid sequence that will prove to be functionally important in a wide variety of proteins.

Recent evidence suggests that fibroblast growth factor (FGF) is a primary mesoderm inducer in Xenopus development. We have isolated a full-length cDNA clone for the Xenopus FGF receptor. Like other FGF receptors, the Xenopus homolog is a membrane-spanning protein with a split intracellular tyrosine kinase domain. The Xenopus FGF receptor mRNA is present as a maternal message whose levels are constant through early development. There is no specific regional localization of the transcript by analysis of FGF receptor mRNA levels in microdissected embryonic tissue. In isolated animal-pole blastomeres, FGF receptor mRNA declines over 16 hr in culture and this loss can be prevented by incubation with FGF or activin. Despite the presence of the FGF receptor mRNA in the oocyte, oocytes in culture do not respond to added FGF. However, injection of exogenous Xenopus FGF receptor transcripts into oocytes does generate a functional response to FGF. Our data suggest that posttranscriptional response to FGF. Our data suggest that posttranscriptional mechanisms regulate the FGF receptor in the oocyte and early embryo and further suggest that mesoderm-inducing factors influence receptor mRNA levels during the time of early tissue formation.

INTRODUCTIONManipulating genes specifically during later stages of amphibian embryonic development requires fine control over the time and place of expression. These protocols describe an efficient nuclear-transplantation-based method of transgenesis developed for Xenopus laevis. The approach enables stable expression of cloned gene products in Xenopus embryos. Because the transgene integrates into the genome prior to fertilization, the resulting embryos are not chimeric, eliminating the need to breed to the next generation to obtain nonmosaic transgenic animals. The procedure is based on restriction-enzyme-mediated integration (REMI) and can be divided into three parts: (I) high-speed preparation of egg extracts, (II) sperm nuclei preparation, and (III) nuclear transplantation. This protocol describes a method for the preparation of sperm nuclei from Xenopus laevis. Sperm suspensions are prepared by filtration and centrifugation, and then treated with lysolecithin to disrupt the plasma membrane of the cells. Sperm nuclei can be stored frozen in small aliquots at -80°C.

The frog transgenesis technique ultimately promises to make mutagenesis possible through random insertion of plasmid DNA into the genome. This study was undertaken to evaluate whether a gene trap approach combined with transgenesis would be appropriate for performing insertional mutagenesis in Xenopus embryos. Firstly, we confirmed that the transgenic technique results in stable integration into the genome and that transmission through the germline occurs in the expected Mendelian fashion. Secondly, we developed several gene trap vectors, using the green fluorescent protein (GFP) as a marker. Using these vectors, we trapped several genes in Xenopus laevis that are expressed in a spatially restricted manner, including expression in the epiphysis, the olfactory bulb and placodes, the eyes, ear, brain, muscles, tail and intestine. Finally, we cloned one of the trapped genes using 5′ rapid amplification of cDNA ends polymerase chain reaction (RACE PCR). These results suggest that the transgenic technique combined with a gene trap approach might provide a powerful method for generating mutations in endogenous genes in Xenopus .

The main objective of this investigation was to induce (create) corneal astigmatism, with a minimum of surgery, using relaxing incisions that are a combination of arc and radial keratotomies. With this combination we were able to induce large, short-term amounts of astigmatism (up to 20 diopters in rabbits). To obtain the maximum surgical effect, the arc keratotomy must be done in the middle zone of the cornea. We also report the theoretical basis to predict mathematically the desired correction.

Les auteurs decrivent une nouvelle technique chirurgicale pour la correction de la myopie et de l'astigmatisme

The mechanical behavior of athe iris-lens-zonule-ciliary body (ILZC) system under intraocular pressure variations, measured with Scan A, is studied on a series of 20 rabbit eyes. The experiments indicate that the ILZC system behaves like a partition between the anterior and vitreous chambers and not like a supporting structural member. The observed behavior is related to previous clinical observations and to the biostructural model of the eye described in a previous paper by the authors.

Induced deformations, similar to the posterior pole deformations due to advanced myopia, were studied in a series of 30 rabbits. The induced deformations were produced by means of a specially designed cup. An analysis of the applicability of the shell theory is made, and it is concluded that the thin shell theory is applicable to the mechanical study of the eyes. The basic experiment consisted of introducing a controlled deformation at different pressure levels; a wide range of types of increments and times of substained deformations were studied. It is concluded that the scleral tissue is an elastic material and has a fairly high 'Creep' rate. The material properties indicate that the eye can reaccommodate induced pressure, and thus glaucoma and myopia could be present without external indications of 'high pressure' in the eye.

The centromere region of Saccharomyces cerevisiae chromosome III has been replaced by various DNA fragments from the centromere regions of yeast chromosomes III and XI. A 289-base pair centromere (CEN3) sequence can stabilize yeast chromosome III through mitosis and meiosis. The orientation of the centromeric fragments within chromosome III has no effect on the normal mitotic or meiotic behavior of the chromosome. The structural integrity of the centromere region in these genomic substitution strains was examined by mapping nucleolytic cleavage sites within the chromatin DNA. A nuclease-protected centromere core of 220-250 base pairs was evident in all of the genomic substitution strains. The position of the protected region is determined strictly by the centromere DNA sequence. These results indicate that the functional centromere core is contained within 220-250 base pairs of the chromatin DNA that is structurally distinct from the flanking nucleosomal chromatin.

The recently described Spred protein family has been implicated in the modulation of receptor tyrosine kinase signalling. We report the crystal structure of the Enabled/vasodilator-stimulated phosphoprotein homology-1 (EVH1) domain from Xenopus tropicalis Spred1, solved to 1.15 A resolution. This structure confirms that the Spred EVH1 adopts the pleckstrin-homology fold, with a similar secondary structure to Enabled. A translation of one of the peptide-binding groove β-strands narrows this groove, whilst one end of the groove shows structural flexibility. We propose that Spred1 will bind peptides that are less proline-rich than other EVH1 domains, with conformational changes indicating an induced fit.