The Eph family in the patterning of neural development

The Eph family represents the largest subfamily of receptor tyrosine kinases. Its members are predominantly expressed in the developing and adult nervous system. Besides playing an important role in the contact-mediated repulsion of axons, they have recently also been implicated in the control of cell migration. Characteristics of the Eph family are extended promiscuity in the interaction between receptors and ligands, the necessity of membrane attachment of the ligands to exert their function, the lack of induction of mitogenic responses, and the bi-directional signalling of receptors and ligands.     

Opposite phenotypes of hypomorphic and Y766 phosphorylation site mutations reveal a function for Fgfr1 in anteroposterior patterning of mouse embryos

Intercellular communication is needed for both the generation of the mesodermal germ layer and its division into distinct subpopulations. To dissect the functions of fibroblast growth factor receptor-1 (FGFR1) during mouse gastrulation as well as to gain insights into its possible roles during later embryonic development, we have introduced specific mutations into the Fgfr1 locus by gene targeting. Our results show functional dominance of one of the receptor isoforms and suggest a function for the autophosphorylation of site Y766 in the negative regulation of FGFR1 activity. Y766F and hypomorphic mutations in Fgfr1 generate opposite phenotypes in terms of homeotic vertebral transformations, suggesting a role for FGFR1 in patterning the embryonic anteriorposterior axis by way of regulation of Hox gene activity.     

Localization of mRNAs for Rlim-1, the rat Xlim-1 homolog, in the developing rat brain

A simple and simultaneous determination of melatonin and its precursors, serotonin (5-HT) and N-acetylserotonin, was achieved by reversed-phase high-performance liquid chromatography with electrochemical detection. The addition of an ion-pairing agent, sodium 1-octanesulfonate, to the chromatographic mobile phase caused an increase of the retention time of 5-HT, and resulted in the successful simultaneous resolution of these three indoleamines. This method was used to quantitate these indoleamines in the pineal gland of juvenile golden hamsters.     

Role of Endothelin-1/Endothelin-A receptor-mediated signaling pathway in the aortic arch patterning in mice

INTRODUCTION: Several modalities of catheter ablation have been proposed to eliminate Mahaim pathway conduction. However, limited research has been reported on the electrophysiologic nature of this pathway in its entity. METHODS and RESULTS: In seven patients, electrophysiologic study was performed, and radiofrequency energy was applied to investigate the electrophysiologic clues for successful ablation. In all seven patients, the Mahaim pathway was diagnosed as a right-sided atriofascicular or atrioventricular pathway with decremental properties. In two patients, two different kinds of electrograms were recorded through the ablation catheter positioned at the Mahaim pathway location: one was suggestive of conduction over the decremental portion, demonstrating a dulled potential; and the other of nondecremental conduction, demonstrating a spiked potential. All but one of the Mahaim pathways were eliminated successfully at the atrial origin where the spiked Mahaim potential was recorded. Radiofrequency energy application was performed at the slow potential site resulting in failure to eliminate the conduction over the Mahaim pathway. Conduction block at the site between the slow and fast potential recording sites was provoked by intravenous administration of adenosine, concomitant with a decrease in the amplitude of the Mahaim potential. In one patient, the clinical arrhythmia was a sustained monomorphic ventricular tachycardia originating from the ventricular end of the Mahaim fiber. CONCLUSION: The identification of Mahaim spiked potentials may be the optimal method to permit their successful ablation. Detailed electrophysiologic assessment is indispensable for successful ablation of tachycardias associated with Mahaim fibers because tachycardias unassociated with Mahaim fibers can occur despite complete elimination of the Mahaim fiber.     

GATA-1 inhibits the formation of notochord and neural tissue in Xenopus embryo

To investigate whether rhinovirus infection impairs epithelial barrier functions, human rhinovirus 14 (HRV-14) was infected to primary cultures of human tracheal epithelial cells and experiments were performed on Day 2 after HRV-14 infection. Hydrogen peroxide (H2O2; 3 x 10(-)4 M) increased electrical conductance (G) across the epithelial cell sheet measured with Ussing's chamber methods. Exposure of the epithelial cells to HRV-14 had no effect on H2O2-induced increases in G and [3H]mannitol flux through the cultured epithelium in the control condition, but it markedly potentiated H2O2- induced increases in both parameters in IL-1beta (100 U/ml) pretreated condition. However, pretreatment with TNF-alpha (100 U/ml) was without effect. IL-1beta enhanced the intercellular adhesion molecule-1 (ICAM-1) expression assessed by immunohistochemical analysis and susceptibility of epithelial cells to HRV-14 infection. An antibody to ICAM-1 inhibited HRV-14 infection of epithelial cells and abolished H2O2-induced increases in G and [3H]mannitol flux in IL-1beta-pretreated epithelial cells with HRV-14 infection. These results suggest that rhinovirus infection may reduce barrier functions in the airway epithelium in association with upregulation of ICAM-1 expression.     

Involvement of the sonic hedgehog, patched 1 and bmp2 genes in patterning of the zebrafish dermal fin rays

The signaling molecule encoded by Sonic hedgehog (shh) participates in the patterning of several embryonic structures including limbs. During early fin development in zebrafish, a subset of cells in the posterior margin of pectoral fin buds express shh. We have shown that regulation of shh in pectoral fin buds is consistent with a role in mediating the activity of a structure analogous to the zone of polarizing activity (ZPA) (Akimenko and Ekker (1995) Dev. Biol. 170, 243-247). During growth of the bony rays of both paired and unpaired fins, and during fin regeneration, there does not seem to be a region equivalent to the ZPA and one would predict that shh would play a different role, if any, during these processes specific to fish fins. We have examined the expression of shh in the developing fins of 4-week old larvae and in regenerating fins of adults. A subset of cells in the basal layer of the epidermis in close proximity to the newly formed dermal bone structures of the fin rays, the lepidotrichia, express shh, and ptc1 which is thought to encode the receptor of the SHH signal. The expression domain of ptc1 is broader than that of shh and adjacent blastemal cells releasing the dermal bone matrix also express ptc1. Further observations indicate that the bmp2 gene, in addition to being expressed in the same cells of the basal layer of the epidermis as shh, is also expressed in a subset of the ptc1-expressing cells of the blastema. Amputations of caudal fins immediately after the first branching point of the lepidotrichia, and global administration of all-trans-retinoic acid, two procedures known to cause fusion of adjacent rays, result in a transient decrease in the expression of shh, ptc1 and bmp2. The effects of retinoic acid on shh expression occur within minutes after the onset of treatment suggesting direct regulation of shh by retinoic acid. These observations suggest a role for shh, ptc1 and bmp2 in patterning of the dermoskeleton of developing and regenerating teleost fins.     

A posteriorising factor, retinoic acid, reveals that anteroposterior patterning controls the timing of neuronal differentiation in Xenopus neuroectoderm

During early development of the Xenopus central nervous system (CNS), neuronal differentiation can be detected posteriorly at neural plate stages but is delayed anteriorly until after neural tube closure. A similar delay in neuronal differentiation also occurs in the anterior neural tissue that forms in vitro when isolated ectoderm is treated with the neural inducer noggin. Here we examine the factors that control the timing of neuronal differentiation both in embryos and in neural tissue induced by noggin (noggin caps). We show that the delay in neuronal differentiation that occurs in noggin caps cannot be overcome by inhibiting the activity of the neurogenic gene, X-Delta-1, which normally inhibits neuronal differentiation, suggesting that it represents a novel level of regulation. Conversely, we show that the timing of neuronal differentiation can be changed from late to early after treating noggin caps or embryos with retinoic acid (RA), a putative posteriorising agent. Concommittal with changes in the timing of neuronal differentiation, RA suppresses the expression of anterior neural genes and promotes the expression of posterior neural genes. The level of early neuronal differentiation induced by RA alone is greatly increased by the additional expression of the proneural gene, XASH3. These results indicate that early neuronal differentiation in neuralised ectoderm requires posteriorising signals, as well as signals that promote the activity of proneural genes such as XASH3. In addition, these result suggest that neuronal differentiation is controlled by anteroposterior (A-P) patterning, which exerts a temporal control on the onset of neuronal differentiation.     

Control of dorsoventral somite patterning by Wnt-1 and beta-catenin

In vertebrates, the dorsoventral patterning of somitic mesoderm is controlled by factors expressed in adjacent tissues. The ventral neural tube and the notochord function to promote the formation of the sclerotome, a ventral somite derivative, while the dorsal neural tube and the surface ectoderm have been shown to direct somite cells to a dorsal dermomyotomal fate. A number of signaling molecules are expressed in these inducing tissues during times of active cell fate specification, including members of the Hedgehog, Wnt, and BMP families. However, with the exception of the ventral determinant Sonic hedgehog (Shh), the functions of these signaling molecules with respect to dorsoventral somite patterning have not been determined. Here we investigate the role of Wnt-1, a candidate dorsalizing factor, in the regulation of sclerotome and dermomyotome formation. When ectopically expressed in the presomitic mesoderm of chick embryos in ovo, Wnt-1 differentially affects the expression of dorsal and ventral markers. Specifically, ectopic Wnt-1 is able to completely repress ventral (sclerotomal) markers and to enhance and expand the expression of dorsal (dermomyotomal) markers. However, Wnt-1 appears to be unable to convert all somitic mesoderm to a dermomyotomal fate. Delivery of an activated form of beta-catenin to somitic mesoderm mimics the effects of Wnt-1, demonstrating that Wnt-1 likely acts directly on somitic mesoderm, and not through adjacent tissues via an indirect signal relay mechanism. Taken together, our results support a model for somite patterning where sclerotome formation is controlled by the antagonistic activities of Shh and Wnt signaling pathways.     

Integration of the head and trunk segmentation systems controls cephalic furrow formation in Drosophila

Genetic and molecular analyses of patterning of the Drosophila embryo have shown that the process of segmentation of the head is fundamentally different from the process of segmentation of the trunk. The cephalic furrow (CF), one of the first morphological manifestations of the patterning process, forms at the juxtaposition of these two patterning systems. We report here that the initial step in CF formation is a change in shape and apical positioning of a single row of cells. The anteroposterior position of these initiator cells may be defined by the overlapping expression of the head gap gene buttonhead (btd) and the primary pair-rule gene even-skipped (eve). Re-examination of the btd and eve phenotypes in live embryos indicated that both genes are required for CF formation. Further, Eve expression in initiator cells was found to be dependent upon btd activity. The control of eve expression by btd in these cells is the first indication of a new level of integrated regulation that interfaces the head and trunk segmentation systems. In conjunction with previous data on the btd and eve embryonic phenotypes, our results suggest that interaction between these two genes both controls initiation of a specific morphogenetic movement that separates two morphogenetic fields and contributes to patterning the hinge region that demarcates the procephalon from the segmented germ band.     

Regional cell movement and tissue patterning in the zebrafish embryo revealed by fate mapping with caged fluorescein

Determination of fate maps and cell lineage tracing have previously been carried out in the zebrafish embryo by following the progeny of individual cells injected with fluorescent dyes. We review the information obtained from these experiments and then present an approach to fate mapping and cell movement tracing, utilizing the activation of caged fluorescein-dextran. This method has several advantages over single-cell injections in that it is rapid, allows cells at all depths in the embryo to be marked, can be used to follow cells starting at any time during development, and allows an appreciation of the movements of cells located in a coherent group at the time of uncaging. We demonstrate that the approach is effective in providing additional and complementary information on prospective mesoderm and brain tissues studied previously. We also present, for the first time, a fate map of placodal tissues including the otic vesicle, lateral line, cranial ganglia, lens, and olfactory epithelium. The prospective placodal cells are oriented at the 50% epiboly stage on the ventral side of the embryo with anterior structures close to the animal pole, and posterior structures nearer to the germ ring.     

Leptin and UCP1 genes are reciprocally regulated in brown adipose tissue

In a previous work we showed that only unilocular brown adipocytes express leptin. In order to investigate the relationship between leptin gene expression, brown adipocyte activity (UCP1) and morphology, we studied brown adipose tissues of mice (C57BL, female, 7 weeks old) acclimated at different temperatures (19 degrees C and 28 degrees C). Northern blot analysis revealed higher leptin and lower UCP1 mRNA levels in mice exposed to 28 degrees C than in the group acclimated at 19 degrees C. Also protein expression (immunohistochemistry) differed in the two groups: at 28 degrees C brown adipocytes were positive for leptin and only weakly positive for UCP1, while at 19 degrees C they were leptin-negative and UCP1-positive. In the former group the morphology was mainly unilocular. Our data suggest that in brown adipocytes of warm-acclimated mice leptin expression is closely related to their hypoactive functional stage, as evidenced by their low level of UCP1 synthesis and the morphological rearrangement of the lipid content (unilocularity).     

The roles of the homeobox genes aristaless and Distal-less in patterning the legs and wings of Drosophila

In the leg and wing imaginal discs of Drosophila, the expression domains of the homeobox genes aristaless (al) and Distal-less (Dll) are defined by the secreted signaling molecules Wingless (Wg) and Decapentaplegic (Dpp). Here, the roles played by al and Dll in patterning the legs and wings have been investigated through loss of function studies. In the developing leg, al is expressed at the presumptive tip and a molecularly defined null allele of al reveals that its only function in patterning the leg appears to be to direct the growth and differentiation of the structures at the tip. In contrast, Dll has previously been shown to be required for the development of all of the leg more distal than the coxa. Dll protein can be detected in a central domain in leg discs throughout most of larval development, and in mature discs this domain corresponds to the distal-most region of the leg, the tarsus and the distal tibia. Clonal analysis reveals that late in development these are the only regions in which Dll function is required. However, earlier in development Dll is required in more proximal regions of the leg suggesting it is expressed at high levels in these cells early in development but not later. This reveals a correlation between a temporal requirement for Dll and position along the proximodistal axis; how this may relate to the generation of the P/D axis is discussed. Dll is required in the distal regions of the leg for the expression of tarsal-specific genes including al and bric-a-brac. Dll mutant cells in the leg sort out from wild-type cells suggesting one function of Dll here is to control adhesive properties of cells. Dll is also required for the normal development of the wing, primarily for the differentiation of the wing margin.     

Role of ATP in the mechanism of serotonin absorption by lung tissue

Tests set up on the isolated perfused lungs of albino rats and on intact dogs demonstrated that the serotonin absorption by the pulmonary tissue is attended by a drop of the ATP amount in the lungs. The exogenous ATP has no essential effect on the serotonin absorption by the pulmonary tissue, its considerable quantities being metabolized in the pulmonary capillaries.     

Role of apoptosis in testicular tissue damage caused by varicocele

PURPOSE: During the last few years there has been an increasing interest in evaluating quality of life (QOL) data regarding surgical treatment. METHODS: The present study comments the efficacy of laparoscopic antireflux surgery after required Nissen fundoplication of 70 patients. Therefore, the German Gastrointestinal Quality of Life Index (GIQLI) was used to query the patients preoperatively and three times after surgery up to 1 year. RESULTS: Preoperatively, we found a low general GIQLI score (mean 92.7 points), which increased 6 weeks postoperatively (116.8 points), 3 months (124.8) and 1 year (mean 123.9 points) significantly and is now comparable to the healthy population (122.6 points). CONCLUSION: It is our opinion that the efficacy of the treatment of gastroesophageal reflux disease with required Nissen fundoplication can also be documented and discussed by using QOL.     

Noggin-mediated antagonism of BMP signaling is required for growth and patterning of the neural tube and somite

Embryonic patterning in vertebrates is dependent upon the balance of inductive signals and their specific antagonists. We show that Noggin, which encodes a bone morphogenetic protein (BMP) antagonist expressed in the node, notochord, and dorsal somite, is required for normal mouse development. Although Noggin has been implicated in neural induction, examination of null mutants in the mouse indicates that Noggin is not essential for this process. However, Noggin is required for subsequent growth and patterning of the neural tube. Early BMP-dependent dorsal cell fates, the roof plate and neural crest, form in the absence of Noggin. However, there is a progressive loss of early, Sonic hedgehog (Shh)-dependent ventral cell fates despite the normal expression of Shh in the notochord. Further, somite differentiation is deficient in both muscle and sclerotomal precursors. Addition of BMP2 or BMP4 to paraxial mesoderm explants blocks Shh-mediated induction of Pax-1, a sclerotomal marker, whereas addition of Noggin is sufficient to induce Pax-1. Noggin and Shh induce Pax-1 synergistically. Use of protein kinase A stimulators blocks Shh-mediated induction of Pax-1, but not induction by Noggin, suggesting that induction is mediated by different pathways. Together these data demonstrate that inhibition of BMP signaling by axially secreted Noggin is an important requirement for normal patterning of the vertebrate neural tube and somite.     

Role of chaos in trial-and-error problem solving by an artificial neural network

The effect of heparin as a reversing agent of multidrug resistance (MDR) was tested on normal mononuclear cells from 24 healthy volunteers and leukaemic cells from 12 acute myeloid leukaemia, five chronic myeloid leukaemia, five acute lymphoid leukaemia and three chronic lymphoid leukaemia patients. Two cell lines were used as controls, the human erythroleukaemia K562 and its vincristine-resistant derivative K562-Lucena 1. Heparin was not cytotoxic by itself as determined using a MTT assay and cell counts. MDR modulation was assessed by Rhodamine 123 extrusion using flow-cytometry. Modulation of the resistant cell line was produced by the classical reversing agent verapamil and also by heparin, the same being observed in normal and leukaemic cells and being independent of the type of leukaemia. Our work suggests that heparin may be considered a potential MDR modulator.     

Expression of zebrafish bHLH genes ngn1 and nrd defines distinct stages of neural differentiation

The phenotype of T cells in the central nervous system (CNS) in two models of chronic inflammation (experimental allergic encephalomyelitis and Corynebacterium parvum-induced inflammation) was compared to that of T cells in gut and chronically inflamed subcutaneous tissue and lung. CNS T cells display a similar phenotype in both inflammatory models, and are phenotypically unique compared to T cells from the other inflamed tissues. T cells from inflamed CNS are mainly CD4+ and are the only population examined that express a typical activated/memory phenotype: CD44high/LFA-1high/ICAM-1high/CD45RBlow. The CNS T cells are alpha4beta7-integrin(negative), but express alpha4-integrin and activated beta1 integrin, suggesting expression of the alpha4beta1-heterodimer in an activated state. In contrast, most T cells in gut express low levels of activated beta1 integrin. The CNS T cells lack expression of alpha6 and alphaE integrin chains and L-selectin. In inflamed CNS and inflamed subcutaneous tissue, approximately 50% of T cells express high affinity ligands for P-selectin while fewer than 10% express high affinity ligands for E-selectin. In summary, our data show that, independent of the inflammatory stimulus, T cells recruited into the inflamed CNS are phenotypically distinct from T cells in other inflamed tissues. This finding leads us to hypothesize the existence of a phenotypically distinct 'CNS-seeking' T lymphocyte population.