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J Shih

Publications and source records attributed to J Shih.

52 records · Page 3Linked to original sources
PubMed1993

XASH-3, a novel Xenopus achaete-scute homolog, provides an early marker of planar neural induction and position along the mediolateral axis of the neural plate.

We have isolated a novel Xenopus homolog of the Drosophila achaete-scute genes, called XASH-3. XASH-3 expression is neural specific and is detected as early as stage 11 1/2, making it one of the earliest markers of neural induction so far described. Moreover, XASH-3 expression within the neural plate is regionally restricted. Transverse bands of XASH-3 mRNA mark discrete positions along the anteroposterior axis, while longitudinal bands mark a discrete position along the mediolateral axis. This latter site of XASH-3 expression appears to demarcate the prospective sulcus limitans, a boundary zone that later separates the functionally distinct dorsal (alar) and ventral (basal) regions of the spinal cord. In sandwich explants lacking any underlying mesoderm, XASH-3 is expressed in longitudinal stripes located lateral to the midline. This provides the first indication that planar or midline-derived inductive signals are sufficient to establish at least some aspects of positional identity along the mediolateral axis of the neural plate. By contrast, the transverse stripes of XASH-3 expression are not detected, suggesting that this aspect of anteroposterior neural pattern is lost or delayed in the absence of vertically passed signals. The restricted mediolateral expression of XASH-3 suggests that mediolateral patterning of the neural plate is an early event, and that this regionalization can be achieved in the absence of inducing signals derived from underlying mesoderm.

Animals↗
PubMed1993

Xwnt-5A: a maternal Wnt that affects morphogenetic movements after overexpression in embryos of Xenopus laevis.

To contribute to an understanding of the roles and mechanisms of action of Wnts in early vertebrate development, we have characterized the normal expression of Xenopus laevis Wnt-5A, and investigated the consequences of misexpression of this putative signalling factor. Xwnt-5A transcripts are expressed throughout development, and are enriched in both the anterior and posterior regions of embryos at late stages of development, where they are found primarily in ectoderm, with lower levels of expression in mesoderm. Overexpression of Xwnt-5A in Xenopus embryos leads to complex malformations distinct from those achieved by ectopic expression of Xwnts -1, -3A, or -8. This phenotype is unlikely to result from Xwnt-5A acting as an inducing agent, as overexpression of Xwnt-5A does not rescue dorsal structures in UV-irradiated embryos, does not induce mesoderm in blastula caps, and Xwnt-5A does not alter the endogenous patterns of expression of goosecoid, Xbra, or Xwnt-8. To pursue whether Xwnt-5A has the capacity to affect morphogenetic movements, we investigated whether overexpression of Xwnt-5A alters the normal elongation of blastula cap explants induced by activin. Intriguingly, Xwnt-5A blocks the elongation of blastula caps in response to activin, without blocking the differentiation of either dorsal or ventral mesoderm within these explants. The data are consistent with Xwnt-5A having the potential activity of modifying the morphogenetic movements of tissues.

Amino Acid Sequence↗
PubMed1992

The cellular basis of the convergence and extension of the Xenopus neural plate.

There is great interest in the patterning and morphogenesis of the vertebrate nervous system, but the morphogenetic movements involved in early neural development and their underlying cellular mechanisms are poorly understood. This paper describes the cellular basis of the early neural morphogenesis of Xenopus laevis. The results have important implications for neural induction. Mapping the fate map of the midneurula (Eagleson and Harris: J. Neurobiol. 21:427-440, 1990) back to the early gastrula with time-lapse video recording demonstrates that the prospective hindbrain and spinal cord are initially very wide and very short, and thus at the beginning of gastrulation all their precursor cells lie within a few cell diameters of the inducing mesoderm. In the midgastrula, the prospective hindbrain and spinal cord undergo very strong convergence and extension movements in two phases: In the first phase they primarily undergo thinning in the radial direction and lengthening (extension) in the animal-vegetal direction, and the second phase is characterized primarily by mediolateral narrowing (convergence) and anterior-posterior lengthening (extension). These movements also occur in sandwich explants of the gastrula, thus demonstrating the local autonomy of the forces producing them. Tracing cell movements with fluorescein dextran-labeled cells in embryos or explants shows that the initial thinning and extension occurs by radial intercalation of deep cells to form fewer layers of greater area, all of which is expressed as increased length. The subsequent convergence and extension occurs by mediolateral intercalation of deep cells to form a longer, narrower array. These results establish that a similar if not identical sequence of radial and mediolateral cell intercalations underlie convergence and extension of the neural and the mesoderm tissues (Wilson and Keller: Development, 112:289-300, 1991). Moreover, these results establish that radial and mediolateral intercalation are the principal neural cell behaviors induced by the planar signals emanating from the dorsal involuting marginal zone (the Spemann organizer) in the early gastrula (Keller et al: Develop. Dynamics, 193: 218-234, 1992). Radial and mediolateral intercalation are induced among the 5 to 7 rows of cells comprising the prospective hindbrain and spinal cord, thus producing the massive convergence and extension movements that narrow and elongate these regions of the nervous system in the late gastrula. A more general significance of these results is that neural induction is best analyzed and understood in terms of the dynamics of the morphogenetic processes involved.

Animals↗
PubMed1992

Planar induction of convergence and extension of the neural plate by the organizer of Xenopus.

This paper demonstrates that convergence and extension within the neural plate of Xenopus laevis are regulated by planar inductive interactions with the adjacent Spemann organizer. The companion article (Keller et al.: Developmental Dynamics 193:199-217, 1992) showed that the prospective hindbrain and spinal cord occupy a very short and very wide area just above the Spemann organizer in the early gastrula and that these regions converge and extend greatly during gastrulation and neurulation, using a sequence of radial and mediolateral cell intercalations. In this article, we show that "planar" contact of these regions with the organizer at their vegetal edge until stage 11 is sufficient to induce convergence and extension, after which their convergence and extension become autonomous. Grafts of the organizer in planar contact with uninduced ectodermal tissues induce these ectodermal tissues to converge and extend by a planar inductive signal from the organizer. Labeling of the inducing or responding tissues confirms that only planar interactions occur. Neural convergence and extension are actually hindered in explants deliberately constructed so that vertical interactions occur. These results show unambiguously that the Spemann organizer induces the extraordinary and precocious convergence and extension movements of the Xenopus neural plate by planar interactions acting over short distances.

Animals↗
PubMed1992

The epithelium of the dorsal marginal zone of Xenopus has organizer properties.

We have investigated the properties of the epithelial layer of the dorsal marginal zone (DMZ) of the Xenopus laevis early gastrula and found that it has inductive properties similar to those of the entire Spemann organizer. When grafts of the epithelial layer of the DMZ of early gastrulae labelled with fluorescein dextran were transplanted to the ventral sides of unlabelled host embryos, they induced secondary axes composed of notochord, somites and posterior neural tube. The organizer epithelium rescued embryos ventralized by UV irradiation, inducing notochord, somites and posterior neural tube in these embryos, while over 90% of ventralized controls showed no such structures. Combinations of organizer epithelium and ventral marginal zone (VMZ) in explants of the early gastrula resulted in convergence, extension and differentiation of dorsal mesodermal tissues, whereas similar recombinants of nonorganizer epithelium and the VMZ did none of these things. In all cases, the axial structures forming in response to epithelial grafts were composed of labelled graft and unlabelled host cells, indicating an induction by the organizer epithelium of dorsal, axial morphogenesis and tissue differentiation among mesodermal cells that otherwise showed non-axial development. Serial sectioning and scanning electron microscopy of control grafts shows that the epithelial organizer effect occurs in the absence of contaminating deep cells adhering to the epithelial grafts. However, labelled organizer epithelium grafted to the superficial cell layer contributed cells to deep mesodermal tissues, and organizer epithelium developed into mesodermal tissues when deliberately grafted into the deep region. This shows that these prospective endodermal epithelial cells are able to contribute to mesodermal, mesenchymal tissues when they move or are moved into the deep environment. These results suggest that in normal development, the endodermal epithelium may influence some aspects of the cell motility underlying the mediolateral intercalation (see Shih, J. and Keller, R. (1992) Development 116, 901-914), as well as the tissue differentiation of mesodermal cells. These results have implications for the analysis of mesoderm induction and for analysis of variations in the differentiation and morphogenetic function of the marginal zone in different species of amphibians.

Animals↗
PubMed1992

Cell motility driving mediolateral intercalation in explants of Xenopus laevis.

In Xenopus, convergence and extension are produced by active intercalation of the deep mesodermal cells between one another along the mediolateral axis (mediolateral cell intercalation), to form a narrower, longer array. The cell motility driving this intercalation is poorly understood. A companion paper shows that the endodermal epithelium organizes the outermost mesodermal cells immediately beneath it to undergo convergence and extension, and other evidence suggests that these deep cells are the most active participants in mediolateral intercalation (Shih, J. and Keller, R. (1992) Development 116, 887-899). In this paper, we shave off the deeper layers of mesodermal cells, which allows us to observe the protrusive activity of the mesodermal cells next to the organizing epithelium with high resolution video microscopy. These mesodermal cells divide in the early gastrula and show rapid, randomly directed protrusive activity. At the early midgastrula stage, they begin to express a characteristic sequence of behaviors, called mediolateral intercalation behavior (MIB): (1) large, stable, filiform and lamelliform protrusions form in the lateral and medial directions, thus making the cells bipolar; (2) these protrusions are applied directly to adjacent cell surfaces and exert traction on them, without contact inhibition; (3) as a result, the cells elongate and align parallel to the mediolateral axis and perpendicular to the axis of extension; (4) the elongate, aligned cells intercalate between one another along the mediolateral axis, thus producing a longer, narrower array. Explants of essentially a single layer of deep mesodermal cells, made at stage 10.5, converge and extend by mediolateral intercalation. Thus by stage 10.5 (early midgastrula), expression of MIB among deep mesodermal cells is physiologically and mechanically independent of the organizing influence of the endodermal epithelium, described previously (Shih, J. and Keller, R. (1992) Development 116 887-899), and is the fundamental cell motility underlying mediolateral intercalation and convergence and extension of the body axis.

Animals↗
PubMed1992

Patterns of cell motility in the organizer and dorsal mesoderm of Xenopus laevis.

In a companion paper (Shih, J. and Keller, R. (1992) Development 116, 901-914), we described a sequence of cell behaviors, called mediolateral intercalation behavior (MIB), that produces mediolateral cell intercalation, the process that drives convergence and extension of the axial and paraxial mesoderm of Xenopus. In this paper, we describe the pattern of expression of MIB in the mesoderm during gastrulation, using video image processing and recording of cell behavior in 'shaved', open-faced explants of the marginal zone. At midgastrula stage (10.5), MIB begins at two dorsolateral sites in the prospective anterior mesoderm and progresses medially along two arcs that lengthen toward and meet at the midline to form a single arc of cells expressing MIB, called the vegetal alignment zone (VgAZ). The notochordal-somitic mesodermal boundary forms within the VgAZ at stage 11, and then progresses animally and laterally, along the prospective anterior-posterior axis, eventually bounding a trapezoidal area the shape of the fate-mapped notochord. Meanwhile, from its origin in the VgAZ, MIB spreads in the prospective posterior direction along the lateral boundaries of both the notochordal and somitic mesoderm. From there it spreads medially in both tissues. Subsequently, vacuolation of notochord cells, and segmentation and expression of a somite-specific marker repeat the progression of mediolateral intercalation behavior. Thus cells in the posterior, medial regions of the notochordal and the somitic territories are the last to express mediolateral intercalation behavior and subsequent tissue differentiations. In explants that do not converge, these cells neither express mediolateral intercalation behavior nor differentiate. These facts suggest that progressions of MIB in the anterior-posterior and lateral-medial directions may be organized by signals emanating from the lateral somitic and notochordal boundaries. These signals may have limited range and may be dependent on convergence, driven by mediolateral cell intercalation, to bring cells within their range. In the embryo, the posterior progression of MIB results in arcs of convergence, anchored in the vegetal endoderm at each end, acting on the inside of the blastoporal lip to produce involution of the IMZ.

Animals↗
PubMed1992

The patterning and functioning of protrusive activity during convergence and extension of the Xenopus organiser.

We discuss the cellular basis and tissue interactions regulating convergence and extension of the vertebrate body axis in early embryogenesis of Xenopus. Convergence and extension occur in the dorsal mesoderm (prospective notochord and somite) and in the posterior nervous system (prospective hindbrain and spinal cord) by sequential cell intercalations. Several layers of cells intercalate to form a thinner, longer array (radial intercalation) and then cells intercalate in the mediolateral orientation to form a longer, narrower array (mediolateral intercalation). Fluorescence microscopy of labeled mesodermal cells in explants shows that protrusive activity is rapid and randomly directed until the midgastrula stage, when it slows and is restricted to the medial and lateral ends of the cells. This bipolar protrusive activity results in elongation, alignment and mediolateral intercalation of the cells. Mediolateral intercalation behavior (MIB) is expressed in an anterior-posterior and lateral-medial progression in the mesoderm. MIB is first expressed laterally in both somitic and notochordal mesoderm. From its lateral origins in each tissue, MIB progresses medially. If convergence does not bring the lateral boundaries of the tissues closer to the medial cells in the notochordal and somitic territories, these cells do not express MIB. Expression of tissue-specific markers follows and parallels the expression of MIB. These facts argue that MIB and some aspects of tissue differentiation are induced by signals emanating from the lateral boundaries of the tissue territories and that convergence must bring medial cells and boundaries closer together for these signals to be effective. Grafts of dorsal marginal zone epithelium to the ventral sides of other embryos, to ventral explants and to UV-ventralized embryos show that it has a role in organising convergence and extension, and dorsal tissue differentiation among deep mesodermal cells. Grafts of involuting marginal zone to animal cap tissue of the early gastrula shows that convergence and extension of the hindbrain-spinal cord are induced by planar signals from the involuting marginal zone.

Animals↗
PubMed1992

Serum cholesterol level and mortality findings for men screened in the Multiple Risk Factor Intervention Trial. Multiple Risk Factor Intervention Trial Research Group.

BACKGROUND: With increased efforts to lower serum cholesterol levels, it is important to quantify associations between serum cholesterol level and causes of death other than coronary heart disease, for which an etiologic relationship has been established. METHODS: For an average of 12 years, 350,977 men aged 35 to 57 years who had been screened for the Multiple Risk Factor Intervention Trial were followed up following a single standardized measurement of serum cholesterol level and other coronary heart disease risk factors; 21,499 deaths were identified. RESULTS: A strong, positive, graded relationship was evident between serum cholesterol level measured at initial screening and death from coronary heart disease. This relationship persisted over the 12-year follow-up period. No association was noted between serum cholesterol level and stroke. The absence of an association overall was due to different relationships of serum cholesterol level with intracranial hemorrhage and nonhemorrhagic stroke. For the latter, a positive, graded association with serum cholesterol level was evident. For intracranial hemorrhage, cholesterol levels less than 4.14 mmol/L (less than 160 mg/dL) were associated with a twofold increase in risk. A serum cholesterol level less than 4.14 mmol/L (less than 160 mg/dL) was also associated with a significantly increased risk of death from cancer of the liver and pancreas; digestive diseases, particularly hepatic cirrhosis; suicide; and alcohol dependence syndrome. In addition, significant inverse graded associations were found between serum cholesterol level and cancers of the lung, lymphatic, and hematopoietic systems, and chronic obstructive pulmonary disease. No significant associations were found of serum cholesterol level with death from colon cancer, with accidental deaths, or with homicides. Overall, the inverse association between serum cholesterol level and most cancers weakened with increasing follow-up but did not disappear. The association between cholesterol level and death due to cancer of the lung and liver, chronic obstructive pulmonary disease, cirrhosis, and suicide weakened little over follow-up. CONCLUSIONS: The association of serum cholesterol with specific causes of death varies in direction, strength, gradation, and persistence. Further research on the determinants of low serum cholesterol level in populations and long-term follow-up of participants in clinical trials are necessary to assess whether inverse associations with noncardiovascular disease causes of death are consequences of noncardiovascular disease, whether serum cholesterol level and noncardiovascular disease are both consequences of other factors, or whether these associations are causal.

Adult↗
PubMed1991

Identification of N-acetylglucosamine-binding immunoglobulins in chicken egg yolk and serum distinct from the major mannose-binding immunoglobulins.

An N-acetyl-D-glucosamine (GlcNAc)-binding protein of 170 kDa has been isolated from hen serum and egg yolk. Another GlcNAc-binding protein of higher molecular mass was present only in the serum. The 170 kDa protein co-electrophoresed and co-chromatographed in gel filtration with a chicken IgG, and behaved identical to chicken IgG in double immunodiffusion with goat anti-chicken gamma chain antiserum. The sugar-binding hierarchy for the serum and yolk binding proteins, determined with bovine serum albumin neoglycoproteins, was GlcNAc greater than N-acetyl-D-galactosamine greater than glucose = galactose = L-fucose greater than mannose. This hierarchy was unlike any previously reported GlcNAc-binding proteins. The larger serum binding protein component was shown to be an IgM by double immunodiffusion with goat anti-chicken mu chain antiserum. The serum and yolk GlcNAc-binding proteins comprise a unique set of sugar-binding immunoglobulins distinct from the previously reported hen serum and yolk mannose-binding proteins (Wang et al., 1986).

Acetylglucosamine↗
PubMed1989

Preparation and biodistribution of 1-[2-(3-[125I]iodo-4-aminophenyl)ethyl]-4-[3-(trifluoromethyl) phenyl]piperazine and 1-[2-(3-[125I]iodo-4-azidophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl] piperazine.

The iodinated analogue of 1-[2-(4-aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine (PAPP), IPAPP (4), and the corresponding azido compound azido-IPAPP (5) were synthesized. The corresponding no-carrier-added 125I (T1/2 = 60 days, 35-60 keV) labeled compounds were also prepared. High specific binding was observed from in vitro binding studies using rat brain tissue preparation; Ki = 20 and 17.5 nM against [3H]-5-HT. In vivo biodistribution studies in rats showed that azido-[125I]IPAPP passed through intact blood-brain barrier and localized in the brain. Ex vivo autoradiography of rat brain sections exhibited a diffuse uptake pattern, which may be due to specific and nonspecific binding. The results indicate that IPAPP and azido-IPAPP may not be suitable to image the serotonin receptor in the brain.

Animals↗
PubMed1985

The function and mechanism of convergent extension during gastrulation of Xenopus laevis.

The processes thought to function in Xenopus gastrulation include bottle cell formation, migration of cells on the roof of the blastocoel, and autonomous convergent extension of the circumblastoporal region. A review of recent and classical results shows that only the last accounts for the bulk of the tissue displacement of gastrulation, including spreading of the marginal zone toward the blastopore, involution of the marginal zone, and closure of the blastopore. Microsurgical manipulation and explantation studies, analysed by time-lapse video and cine microscopy, shows that the dorsal circumblastoporal region contains two regions which show either autonomous or semiautonomous convergent extension. The dorsal involuting marginal zone (IMZ) undergoes convergence (narrowing) and extension (lengthening) after its involution, beginning at the midgastrula stage and continuing through neurulation, such that it simultaneously extends posteriorly across the yolk plug and narrows the blastoporal circumference. Concurrently, the corresponding region of the overlying non-involuting marginal zone (NIMZ) begins a complementary convergent extension, but at a greater rate, which spreads vegetally to occupy surface area vacated by the IMZ. Tissue recombination experiments show that the deep cells of the dorsal IMZ bring about convergent extension. Labelling of small populations of these cells with a cell lineage tracer shows that convergent extension involves intercalation of deep cells to form a longer, narrower array. Direct time-lapse video and cine micrography of deep cells in cultured explants show that convergent extension involves radial and circumferential intercalation. Removal of the entire blastocoel roof of the early gastrula, including all or part of the NIMZ, shows that convergent extension of the IMZ alone can bring about its involution and blastopore closure. The role of convergent extension in gastrulation of other amphibians and other metazoans and its significance to related problems in early development are discussed.

Animals↗
PubMedDate not supplied

Fluorescently detectable magnetic resonance imaging agents.

This report describes the synthesis, characterization, and in vivo testing of several bifunctional contrast-enhancing agents for optical and magnetic resonance imaging (MRI) of experimental animals. These new agents integrate the advantages of both techniques since they can be visualized simultaneously by light and MRI microscopy. Employing this strategy allows the same biological structures of a specimen to be studied at dramatically different resolutions and depths. The complexes possess a metal chelator for binding a paramagnetic ion, gadolinium (Gd3+), and a covalently attached fluorescent dye. The first class of complexes are low-molecular weight species that are composed of the macrocyclic tetraamine 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) as the metal-chelating ligand coupled to tetramethylrhodamine. The second class of MRI-enhancing agents are composed of high-molecular weight polymers that are membrane impermeable and once injected into a cell or cells are trapped inside. These complexes possess multiple copies of both the metal-chelator-diethylenetriaminepentaacetic acid (DTPA) and the tetramethylrhodamine attached to a macromolecular framework of either poly(D-lysine) (pdl) or dextran. Images acquired of single cells after injection with these bifunctional agents enabled us to follow the relative motions and reorganizations of different cell layers during amphibian gastrulation and neurulation in Xenopus laevis embryos.

Animals↗