Chemokine and lymph node homing receptor expression on pDC vary by graft source

A randomized clinical trial of BM vs. blood stem cell transplants from unrelated donors showed that more plasmacytoid dendritic cells (pDCs) in BM grafts was associated with better post-transplant survival. Here, we describe differences in homing-receptor expression on pDC to explain observed differences following BM vs. blood stem cell transplantation.

Host bone marrow-derived IL-12 enhances donor T cell engraftment in a mouse model of bone marrow transplantation

Background

Donor cell engraftment is critical for the success of allogeneic bone marrow transplants. Graft failure is a result of donor cells either failing to engraft initially or being eliminated at later time points. Donor cell engraftment is facilitated by donor T cells, which eliminate residual host hemato-lymphoid effector cells such as NK cells and T cells.

Methods

We aimed to explore the role of host hematopoietic cell derived IL-12 on donor cell engraftment in a murine model of BMT. We established radiation chimeras by transplanting C57BL6/J (B6) mice with BM from either congenic B6 mice or IL-12p40 KO mice. These WT → WT or IL-12 KO → WT chimeras then underwent a secondary transplant with allogeneic (FVB) BM. Survival, engraftment, donor T cell expansion, cytokine production by donor T cells, as well as expression of stimulatory markers on donor T cells was analyzed.

Results

Mice whose residual host hematopoietic cells were capable of producing IL-12 had modestly higher survival, higher donor T cell engraftment, and significantly higher donor erythroid engraftment. We have also found that an increased number of donor T cells in IL-12 KO → WT chimeras have a regulatory phenotype, expressing FoxP3, producing lower levels of TNF-α, higher levels of IL-10, and expressing higher levels of ICOS as well as PD-1 on CD4+ T cells.

Conclusions

To our knowledge, this is the first report of a beneficial role of IL-12 production by host cells in the context of bone marrow engraftment in a murine model of BMT. These findings support the clinical use of exogenous IL-12 for use in settings where graft failure is of concern.

Genetic dissection of the photoreceptor system in the compound eye of Drosophila melanogaster

Three mutations which eliminate specific types of photoreceptors in Drosophila were characterized. Of the eight photoreceptors in each facet, two mutations delete the outer six (R 1-6). The third eliminates R 7, one of the two central photoreceptors. Double mutants can be constructed in which only photoreceptor R 8 is present. The spectral sensitivities, photopigments, and behavioural properties of these mutants were investigated. R 1-6 have two sensitivity peaks, near 350 and 470 nm. These receptors contain a rhodopsin with these absorption peaks. It interconverts with a metarhodopsin that absorbs around 570 nm. R 7 is a U.V.-receptor, containing rhodopsin that absorbs around 370 nm and interconverts with a metarhodopsin which absorbs around 470 nm. R 8 is a non-adapting blue-receptor with a third type of rhodopsin. The properties of these photopigments explain the different sensitivities and spectral adaptation phenomena of the various photoreceptors. All the photoreceptors have input into phototaxis. Spectral analysis of this behaviour provides evidence for integration of the input from the different photoreceptors.

Xenopus fibrillin is expressed in the organizer and is the earliest component of matrix at the developing notochord-somite boundary

We identify a Xenopus fibrillin homolog (XF), and show that its earliest developmental expression is in presumptive dorsal mesoderm at gastrulation, and that XF expression is regulated by mesoderm-inducing factors in animal cap assays. XF protein is also first detected in presumptive mesoderm, but is concentrated specifically into extracellular-matrix structures that begin to develop de novo by mid-gastrulation at both of the bilateral presumptive notochord-somite boundaries. Later in embryogenesis, XF protein is localized to the extracellular matrix at tissue boundaries, where it is found surrounding the notochord, the somites, and the neural tube, as well as under the epidermis. This pattern of protein deposition combines to give the appearance of an "embryonic skeleton," suggesting that one role for XF is to serve as a mechanical element in the embryo prior to bone deposition.

The role of combinational coding by homeodomain and bHLH transcription factors in retinal cell fate specification

Two major families of transcription factors (TFs), basic helix-loop-helix (bHLH) and homeodomain (HD), are known to be involved in cell fate identity. Some recent findings suggest that these TFs are used combinatorially to code for cellular determination in the retina. However, neither the extent nor the efficiency of such a combinatorial coding mechanism has been tested. To look systematically for interactions between these two TF types that would address these questions, we used a matrix analysis. We co-expressed each of six retinally expressed bHLH TFs (XNeuroD; XNgnr-1; Xath3; Xath5; Xash1; Xash3) with each of eight retinally expressed HD TFs (XRx1; XOptx2; XSix3; XPax6; XOtx2; XOtx5b; XBH; XChx10) in retinal progenitors of Xenopus laevis using targeted lipofection. The effects of each of these combinations were assayed on the six major cell types in the retina: Retinal ganglion cells (GCs), Amacrines (ACs), Bipolars (BCs), Horizontals (HCs), Photoreceptors (PRs), and Muller cells (MCs), creating 288 result categories. Multiple-way ANOVA indicated that in 14 categories, there were interactions between the two TFs that produced significantly more or less of a particular cell type than either of the components alone. However, even the most effective combinations were incapable of generating more than 65% of any particular cell type. We therefore used the same techniques to misexpress selected combinations of three TFs in retinal progenitors, but found no further enhancements of particular cell fates, indicating that other factors are probably involved in cell type specification. To test whether particular combinations were essential for horizontal fates, we made VP16 and EnR fusion constructs of some of the factors to provide dominant negative transcriptional activities. Our results confirmed that normal activities of certain combinations were sufficient, and that individually these activities were important for this fate.

The zebrafish as a tool for understanding the biology of visual disorders

Retinal degenerations are the commonest cause of blindness in the Western world, affecting 5% of the population, yet remain largely untreatable. A better understanding of the mechanisms of disease is needed. Zebrafish fill a gap in the current repertoire of models, offering genetic tractability in a vertebrate. Their retina has many similarities with a human retina. Importantly, unlike rodents, they have rich colour vision, offering the potential to model the macular degenerations. A variety of physiological assays, genetic manipulations and histological tools have been developed and useful models of human disease created.

Cellular competence plays a role in photoreceptor differentiation in the developing Xenopus retina

Factors in the environment appear to be responsible for inducing many of the cell fates in the retina, including, for example, photoreceptors. Further, there is a conserved order of histogenesis in the vertebrate retina, suggesting that a temporal mechanism interacts in the control of cellular determination. The temporal mechanism involved could result from different inducing signals being released at different times. Alternatively, the inducing signals might be present at many stages, but an autonomous clock could regulate the competence of cells to respond to them. To differentiate between these mechanisms, cells from young embryonic retinas were dissociated and grown together with those from older embryos, and the timing of photoreceptor determination assayed. Young cells appeared uninfluenced by older cells, expressing photoreceptor markers on the same time schedule as when cultured alone. A similar result was obtained when the heterochronic mixing was done in vivo by grafting a small plug of optic vesicle from younger embryos into older hosts. Even the graft cells at the immediate margin of the transplant failed to express photoreceptor markers earlier than normal, despite their being in contact with older, strongly expressing host cells. We conclude that retinal progenitors intrinsically acquire the ability to respond to photoreceptor-inducing cues by a mechanism that runs on a cell autonomous schedule, and that the conserved order of histogenesis is based in part on this competence clock.

Semaphorin 3A elicits stage-dependent collapse, turning, and branching in Xenopus retinal growth cones

The semaphorin receptor, neuropilin-1 (NP-1), was first identified in Xenopus as the A5 antigen and is expressed abundantly in developing retinal ganglion cells (RGCs). Here we show that growth cones acquire responsiveness to semaphorin 3A (Sema 3A) with age and that the onset of responsiveness correlates with the appearance of NP-1 immunoreactivity. Growth cones from "old" (stage 35/36) retinal explants collapse rapidly (5-10 min) in response to Sema 3A and turn away from a gradient of Sema 3A, whereas "young" growth cones (stage 24) are insensitive to Sema 3A. Moreover, transfection of full-length NP-1 into young neurons confers premature Sema 3A sensitivity. When young neurons are aged in culture they develop Sema 3A sensitivity in parallel with those in vivo, suggesting that an intrinsic mechanism of NP-1 regulation mediates this age-dependent change. Sema 3A-induced collapse is transient, and after recovery approximately 30% of growth cones extend new branches within 1 hr, implicating Sema 3A as a branching factor. Pharmacological inhibitors were used to investigate whether these three Sema 3A-induced behaviors (collapse, turning, and branching) use distinct second messenger signaling pathways. All three behaviors were found to be mediated via cGMP. In situ hybridization shows that Sema 3A is expressed in the tectum and at the anterior boundary of the optic tract where axons bend caudally, suggesting that Sema 3A/NP-1 interactions play a role in guiding axons in the optic tract and in stimulating terminal branching in the tectum.

Temporal coordinates: the genes that fix cell fate with birth order

Drosophila neuroblasts sequentially express a set of four transcription factors that specify the fates of their progeny according to the successive order of their generation. In analogy to spatial coordinate genes that specify neuroblasts by position, these sequentially expressed genes can be called "temporal coordinate genes."

Changing patterns of hospitalization in eating disorder patients

OBJECTIVE

This study investigated the changing patterns of hospitalization of eating disorder patients over the past 15 years.

METHOD

The records of 1,185 eating disorder patients between 1984 and 1998 were examined on several variables.

RESULTS

Over the 15 years, the number of first admissions increased from 20 to 182. There was a concomitant decrease in length of stay from 149.5 days in 1984 to 23.7 days in 1998. Readmissions increased markedly from 0% during the first year to 27% of total admissions in 1998. The discharge weight of anorectic patients significantly decreased from a body mass index (BMI) of 19.3 in 1984 to 17.7 in 1998. These changes were particularly salient in the past 3 years, concurrent with a dramatic rise in managed care cases.

CONCLUSIONS

Over the past 15 years, eating disorder hospital treatment has metamorphozed from long-term treatment of a disorder to stabilization of acute episodes. For some patients, this change has been deleterious and not cost effective.

Cell cycle and cell fate in the nervous system

Recently, a number of molecules originally thought to have a primary role in cell determination have been shown to affect the cell cycle at specific check points, while other molecules discovered for their roles in the cell cycle progression are known to affect the determination and differentiation of neurons. These discoveries have led to a more detailed investigation of the complex molecular machinery that co-ordinates proliferation and differentiation.

Retinal stem cells in vertebrates

In fish and amphibia, retinal stem cells located in the periphery of the retina, the ciliary marginal zone (CMZ), produce new neurons in the retina throughout life. In these species, the retina grows to keep pace with the enlarging body. When birds or mammals reach adult proportions, however, their retinas stop growing so there appears to be no need for such a proliferative area with stem cells. It is a surprise, therefore, that recent data suggest that a region similar to the CMZ of fish and amphibia exists in the postnatal chick and the adult mouse.

Retinal stem cells in vertebrates

In fish and amphibia, retinal stem cells located in the periphery of the retina, the ciliary marginal zone (CMZ), produce new neurons in the retina throughout life. In these species, the retina grows to keep pace with the enlarging body. When birds or mammals reach adult proportions, however, their retinas stop growing so there appears to be no need for such a proliferative area with stem cells. It is a surprise, therefore, that recent data suggest that a region similar to the CMZ of fish and amphibia exists in the postnatal chick and the adult mouse.

The multiple decisions made by growth cones of RGCs as they navigate from the retina to the tectum in Xenopus embryos

Retinal ganglion cells (RGCs) of Xenopus laevis send axons along a stereospecific pathway from the retina to their target the optic tectum. Viewed from the point of the growth cone, this journey is reflected by discrete processes of axon initiation, axon outgrowth, navigation, target recognition, and innervation. These processes are characterised by distinct signalling mechanisms that trigger dynamic changes in growth cone morphology and behavior. Here we review work primarily from our laboratory, examining these events from a cellular and molecular perspective, focusing on the roles of FGFs, netrins, receptors, and intracellular effectors.

Seminal plasma trace metal levels in industrial workers

This study compares the seminal plasma trace metal levels of hospital workers with groups of industrial workers in a petroleum refinery, smelter, and chemical plant. The metals measured were the essential metals (copper, zinc, nickel, cobalt, and manganese) and the toxic metals (lead, cadmium, and aluminum). The group mean +/- SE metal level for each group (50 subjects per group) was calculated, and the statistical significance of the group mean differences of the industrial groups with the hospital group (control) was determined by the Student's t-test. The differences observed in the smelter group were increased copper and zinc (p < or = 0.001) and decreased nickel, cobalt, and manganese (p < or = 0.001, < or = 0.01). The refinery group differences were increased copper, zinc, and nickel (p < or = 0.001) but decreased cobalt and manganese (p < or = 0.001). The chemical group differences were increased zinc (p < or = 0.001) and decreased cobalt (p < or = 0.001). The seminal plasma levels of the toxic metals lead and aluminum were increased in each of the industrial groups (p < or = 0.001). Concurrent differences were (1) decreased accumulation of nickel, cobalt, and manganese in the smelter group, (2) decreased cobalt and manganese in the refinery group, and (3) only decreased cobalt in the chemical group.

Ephrin-B regulates the Ipsilateral routing of retinal axons at the optic chiasm

In Xenopus tadpoles, all retinal ganglion cells (RGCs) send axons contralaterally across the optic chiasm. At metamorphosis, a subpopulation of EphB-expressing RGCs in the ventrotemporal retina begin to project ipsilaterally. However, when these metamorphic RGCs are grafted into embryos, they project contralaterally, suggesting that the embryonic chiasm lacks signals that guide axons ipsilaterally. Ephrin-B is expressed discretely at the chiasm of metamorphic but not premetamorphic Xenopus. When expressed prematurely in the embryonic chiasm, ephrin-B causes precocious ipsilateral projections from the EphB-expressing RGCs. Ephrin-B is also found in the chiasm of mammals, which have ipsilateral projections, but not in the chiasm of fish and birds, which do not. These results suggest that ephrin-B/EphB interactions play a key role in the sorting of axons at the vertebrate chiasm.

Determination of vertebrate retinal progenitor cell fate by the Notch pathway and basic helix-loop-helix transcription factors

The retina is an excellent system in which to study neural cell fate decision mechanisms. It is an organized laminated structure with a limited array of cell types. During the last 5 years, experiments that perturb normal gene expression have highlighted some molecular mechanisms involved in cellular fate choice in the retina. By controlling when a retinoblast is allowed to differentiate, Delta-Notch signaling plays a critical role in the generation of neuronal diversity in the vertebrate retina. When cells are released from the inhibition mediated by the Delta-Notch pathway, basic helix-loop-helix (bHLH) transcription factors act as intrinsic factors that bias neuroblasts towards particular fates. In this review, we present an overview of the data leading to these conclusions on the role of the Delta-Notch pathway and the bHLH proteins on cell fate decisions during vertebrate retinogenesis.

Amniotic fluid B12, calcium, and lead levels associated with neural tube defects

The group mean differences and relationships between folate, B12, calcium, lead, and methionine levels in amniotic fluid from 29 non-NTD and 11 NTD pregnancies (15-20 weeks' gestation age) were determined. The study population was predominantly Hispanic in both groups (48% in non-NTD and 36% in NTD group) with an average maternal age of 29 years in the non-NTD group and 24 years in the NTD group; and, an average gestation age of 18.5 weeks in the non-NTD and 17.5 weeks in the NTD group. The folate, B12, lead, calcium, and methionine levels of the two groups were compared by Student's t-test and by Pearson's correlation. The NTD levels were lower for calcium (p< or =0.0001), B12 (p< or =0.001), and methionine (P< or =0.001); but, the lead level was higher (p< or =0.0001). A negative correlation was observed between lead and both B12 (p< or =0.007) and methionine (p< or =0.02).

X-ngnr-1 and Xath3 promote ectopic expression of sensory neuron markers in the neurula ectoderm and have distinct inducing properties in the retina

Xath3 encodes a Xenopus neuronal-specific basic helix-loop-helix transcription factor related to the Drosophila proneural factor atonal. We show here that Xath3 acts downstream of X-ngnr-1 during neuronal differentiation in the neural plate and retina and that its expression and activity are modulated by Notch signaling. X-ngnr-1 activates Xath3 and NeuroD by different mechanisms, and the latter two genes crossactivate each other. In the ectoderm, X-ngnr-1 and Xath3 have similar activities, inducing ectopic sensory neurons. Among the sensory-specific markers tested, only those that label cranial neurons were found to be ectopically activated. By contrast, in the retina, X-ngnr-1 and Xath3 overexpression promote the development of overlapping but distinct subtypes of retinal neurons. Together, these data suggest that X-ngnr-1 and Xath3 regulate successive stages of early neuronal differentiation and that, in addition to their general proneural properties, they may contribute, in a context-dependent manner, to some aspect of neuronal identity.

The effect of ascorbic acid supplementation on the nicotine metabolism of smokers

BACKGROUND

The relationship of serum ascorbic acid (AA) levels and excretion of nicotine metabolites was determined in 75 men who smoked at least one pack of cigarettes per day.

METHODS

The subjects were randomly divided into three groups of 25 each who received a placebo, 200 mg of supplementation, or 1000 mg of supplementation of AA per day for 1 month. Baseline and weekly serum AA levels were determined and simultaneous estimates of urinary excretion of nicotine metabolites as cotinine equivalents (CE).

RESULTS

The group mean serum AA levels in the placebo group decreased 13% after 2 weeks; the group mean serum levels of the supplemented groups increased significantly after 1 week (P </= 0. 001) and remained elevated over 100% per week from baseline throughout the study. There was a progressive increase in urinary CE excretion in the placebo group. In the supplemented groups, group mean CE excretion decreased an average of 5% weekly in the 200-mg group and an average of 33% weekly in the 1000-mg group. Pearson's correlation between serum AA and urine CE excretion was significant (r = -0.7980, P </= 0.0003).

CONCLUSIONS

Body levels of AA affect the level of urinary nicotine metabolites. The results of this study indicate that dietary levels of AA are inversely correlated to urinary excretion of nicotine metabolites and may be due to suppressed: (1) nicotine intake by smokers who smoked fewer cigarettes or inhale less deeply, (2) nicotine metabolism, or (3) both.

p27Xic1, a Cdk inhibitor, promotes the determination of glial cells in Xenopus retina

p27Xic1, a member of the Cip/Kip family of Cdk inhibitors, besides its known function of inhibiting cell division, induces Müller glia from retinoblasts. This novel gliogenic function of p27Xic1 is mediated by part of the N-terminal domain near but distinct from the region that inhibits cyclin-dependent kinases. Cotransfections with dominant-negative and constitutively active Delta and Notch constructs indicate that the gliogenic effects of p27Xic1 work within the context of an active Notch pathway. The gradual increase of p27Xic1 in the developing retina thus not only limits the number of retinal cells but also increasingly favors the fate of the last cell type to be born in the retina, the Müller glia.

Genetic disorders of vision revealed by a behavioral screen of 400 essential loci in zebrafish

We examined optokinetic and optomotor responses of 450 zebrafish mutants, which were isolated previously based on defects in organ formation, tissue patterning, pigmentation, axon guidance, or other visible phenotypes. These strains carry single point mutations in >400 essential loci. We asked which fraction of the mutants develop blindness or other types of impairments specific to the visual system. Twelve mutants failed to respond in either one or both of our assays. Subsequent histological and electroretinographic analysis revealed unique deficits at various stages of the visual pathway, including lens degeneration (bumper), melanin deficiency (sandy), lack of ganglion cells (lakritz), ipsilateral misrouting of axons (belladonna), optic-nerve disorganization (grumpy and sleepy), inner nuclear layer or outer plexiform layer malfunction (noir, dropje, and possibly steifftier), and disruption of retinotectal impulse activity (macho and blumenkohl). Surprisingly, mutants with abnormally large or small eyes or severe wiring defects frequently exhibit no discernible behavioral deficits. In addition, we identified 13 blind mutants that display outer-retina dystrophy, making this syndrome the single-most common cause of inherited blindness in zebrafish. Our screen showed that a significant fraction (approximately 5%) of the essential loci also participate in visual functions but did not reveal any systematic genetic linkage to particular morphological traits. The mutations uncovered by our behavioral assays provide distinct entry points for the study of visual pathways and set the stage for a genetic dissection of vertebrate vision.

The neuronal architecture of Xenopus retinal ganglion cells is sculpted by rho-family GTPases in vivo

Dendritogenesis, axonogenesis, pathfinding, and target recognition are all affected in distinct ways when Xenopus retinal ganglion cells (RGCs) are transfected with constitutively active (ca), wild-type (wt), and dominant negative (dn) Rho-family GTPases in vivo. Dendritogenesis required Rac1 and Cdc42 activity. Moreover, ca-Rac1 caused dendrite hyperproliferation. Axonogenesis, in contrast, was inhibited by ca-Rac1. This phenotype was partially rescued by the coexpression of dn cyclin-dependent kinase (Cdk5), a proposed effector of Rac1, suggesting that Rac1 activity must be regulated tightly for normal axonogenesis. Growth cone morphology was particularly sensitive to dn-RhoA and wt-Cdc42 constructs. These also caused targeting errors, such as tectal bypass, suggesting that cytoskeletal rearrangements are involved in target recognition and are transduced by these pathways.

Giant eyes in Xenopus laevis by overexpression of XOptx2

Overexpression of XOptx2, a homeodomain-containing transcription factor expressed in the Xenopus embryonic eye field, results in a dramatic increase in eye size. An XOptx2-Engrailed repressor gives a similar phenotype, while an XOptx2-VP16 activator reduces eye size. XOptx2 stimulates bromodeoxyuridine incorporation, and XOptx2-induced eye enlargement is dependent on cellular proliferation. Moreover, retinoblasts transfected with XOptx2 produce clones of cells approximately twice as large as control clones. Pax6, which does not increase eye size alone, acts synergistically with XOptx2. Our results suggest that XOptx2, in combination with other genes expressed in the eye field, is crucially involved in the proliferative state of retinoblasts and thereby the size of the eye.

The effect of ascorbic acid supplementation on the blood lead levels of smokers

BACKGROUND

The study subjects were 75 adult men (20 to 30 years of age), who smoked one pack of cigarettes per day (minimum) and had no clinical signs of ascorbic acid deficiency or lead toxicity. None had a history of industrial exposure to lead, and the blood-lead levels were anticipated to be below 1.45 micromol/L, the minimum blood level associated with toxicity symptoms.

METHODS

The men were randomly assigned to three study groups of 25, and each group was provided a four-week supply of one level of daily ascorbic acid supplements (placebo, 200 mg or 1000 mg of ascorbic acid). We measured baseline and weekly serum and urine ascorbic-acid levels as well as blood and urine lead levels. The weekly group means and variations of the measured data were statistically compared by means of ANOVA and Pearson's correlation.

RESULTS

The serum ascorbic-acid levels of the groups receiving ascorbic acid increased significantly after one week (p< or =.001). There was no effect of placebo or 200 mg ascorbic-acid supplementation on the blood or urine lead levels. However, there was a 81% decrease in blood-lead levels in the 1000 mg ascorbic acid group after one week of supplementation (p< or =.001).

CONCLUSIONS

Daily supplementation with 1000 mg of ascorbic acid results in a significant decrease of blood-lead levels associated with the general population. Ascorbic acid supplementation may provide an economical and convenient method of reducing blood-lead levels, possibly by reducing the intestinal absorption of lead.

Amniotic fluid amino and nucleic acid in normal and neural tube defect pregnancies. A comparison

OBJECTIVE

To explore the relationship between fetal amino acids (AAs), which are the components of structural proteins and nucleic acids, and the changes associated with neural tube defects (NTD).

STUDY DESIGN

Ten weekly amniotic fluid (AF) samples from normal pregnancies (non-NTD) and 10 from NTD pregnancies between 16 and 20 weeks' gestational age were analyzed for AAs, and the weekly average for the non-NTD and NTD groups was determined. The group mean levels were compared by ANOVA.

RESULTS

The weekly group mean levels of methionine, serine and aspartic acid were significantly lower than the weekly group mean levels of the other AAs. The group mean levels of methionine were significantly lower for NTD than for non-NTD pregnancies.

CONCLUSION

The mean methionine level in NTD pregnancies was the only AA alteration in NTD. Although the AF levels of the non-NTD pregnancies showed that the levels of serine, aspartic acid and methionine were 3- to 19-fold lower than those of the other AAs, only methionine is essential. Consequently, methionine is rate limiting with respect to the role of structural proteins and nucleic acids in the fetus.

Properties of ectopic neurons induced by Xenopus neurogenin1 misexpression

We have examined cells cultured from ectoderm-misexpressing Neurogenin1 (Ngn1) to describe better the extent to which this gene can control aspects of neuronal phenotype including motility, morphology, excitability, and synaptic properties. Like primary spinal neurons which normally express Ngn1, cells in Ngn1-misexpressing cultures exhibit a motility-correlated behavior called circus movements prior to neuritogenesis. Misexpression of NeuroD also causes circus movements and later neuronal differentiation. GSK3beta, which inhibits NeuroD function in vivo, blocks both Ngn1-induced and NeuroD-induced neuronal differentiation, while Notch signaling inhibits only Ngn1-induced neuronal differentiation, confirming that NeuroD is downstream of Ngn1 and insensitive to Notch inhibition. While interfering with NeuroD function in ventral ectoderm inhibits both circus movements and neuronal differentiation, such inhibition in the neural plate inhibits only neuronal differentiation, suggesting that additional factors regulate circus movements in the neural ectoderm. Ngn1-misexpressing cells extend N-tubulin-positive neurites and exhibit tetrodotoxin-sensitive action potentials. Unlike the majority of cultured spinal neurons, however, Ngn1-misexpressing cells do not respond to glutamate and do not form functional synapses with myocytes, suggesting that these cells are either like Rohon-Beard sensory neurons or are not fully differentiated.

A critical window for cooperation and competition among developing retinotectal synapses

In the developing frog visual system, topographic refinement of the retinotectal projection depends on electrical activity. In vivo whole-cell recording from developing Xenopus tectal neurons shows that convergent retinotectal synapses undergo activity-dependent cooperation and competition following correlated pre- and postsynaptic spiking within a narrow time window. Synaptic inputs activated repetitively within 20 ms before spiking of the tectal neuron become potentiated, whereas subthreshold inputs activated within 20 ms after spiking become depressed. Thus both the initial synaptic strength and the temporal order of activation are critical for heterosynaptic interactions among convergent synaptic inputs during activity-dependent refinement of developing neural networks.

The genetic sequence of retinal development in the ciliary margin of the Xenopus eye

The ciliary marginal zone is a perpetually self-renewing proliferative neuroepithelium at the perimeter of the retina in amphibians and fish. In the ciliary marginal zone (CMZ), cells are spatially ordered with respect to cellular development, deep stem cells being most peripheral and differentiating retinal progenitors being most central. This spatial gradient in the CMZ recapitulates embryonic retinogenesis and provides a powerful system to examine the relative order of gene expression during this process. A number of neurogenic and proneural genes have been described to have interacting roles in the development of the vertebrate nervous system, and so it is of major importance to put these genes in a hierarchical pathway. In no other system yet described are the developmental stages of neurogenesis arrayed so clearly in a spatial pattern as in the CMZ. We have therefore taken advantage of this system, using double in situ hybridizations on cross sections of the CMZ, to compare the spatial patterns of 15 proneural, neurogenic, and other genes involved in early and late phases of retinal development. In addition, we have positioned these expression patterns with respect to cell division. What emerges from this work is a spatial ordering of gene expression that predicts a genetic hierarchy governing vertebrate retinogenesis. By injecting messenger RNA for some of these genes into blastomeres of the Xenopus embryo and examining the effects on expression of the putative downstream genes, we have been able to corroborate some of the relationships between genes predicted to act sequentially.

Molecular recapitulation: the growth of the vertebrate retina

In postembryonic lower vertebrates, the ciliary marginal zone (CMZ) of the retina is a continuously growing zone in the central nervous system. By studying the cellular and molecular biology of the cells in this region, we have discovered that the CMZ can be divided into several zones, from peripheral to central, which reflect different stages of development of retinal stem cells. Based on the behavior of the cells and on the genes expressed in different regions, we propose here that cellular development in the CMZ recapitulates in space what happens in embryonic retinal development in time.

Sequential genesis and determination of cone and rod photoreceptors in Xenopus

In this study, we addressed the temporal sequence of photoreceptor fate determination in Xenopus laevis by examining a number of key events during early cone and rod development. We compared the relative timing and spatial pattern of cone and rod specification using a number of cell type-specific markers, including probes to a long wavelength-sensitive opsin which is expressed by the major cone subtype. Our results show that cones are initially more numerous, and can arise in less mature regions of the retina than rods, although both types of photoreceptors begin to express their respective opsins at about the same time. We applied these markers to an assay of cellular determination to identify the stages of embryonic development at which the earliest photoreceptor fates are induced in vivo. The relative birth order of the major cone and rod subtypes was revealed by simultaneous labeling with markers of cell proliferation and terminal differentiation. Although there is much temporal overlap between the periods of cone and rod genesis and determination in Xenopus, we could discern that the earliest cones are both born and determined before the first rods. Thus, even in the rapidly developing retina of Xenopus, photoreceptors achieve their identities in a sequential fashion, suggesting that the inductive cues which determine specific photoreceptor fates may also arise sequentially during development.

Target selection: invasion, mapping and cell choice

Recent research has shown that changes in the concentration of particular molecules lead axons to invade their target, and that concentration changes in other molecules at the borders of the target prevent axons from leaving the target area. After invasion, topographic and lamina-specific cues guide axons to the correct location within the target field. At the level of a single cell or part of a cell, the evidence raises the possibility that axon targeting might be a combinatorial affair whereby specific axons compare the relative concentrations of several molecules on the surface of postsynaptic cells in order to choose a particular target. Both proteins and carbohydrates of various classes play major roles in these processes.

Eating disorders

The eating disorders remain perplexing treatment challenges. These disorders are best understood through the clustering of their symptoms and with a multidimensional model. Treatment must follow from the observed symptoms and cannot always follow a standardized course as is done in other psychiatric disorders. CBT is the most efficacious treatment for both AN and BN.

Comparison of sperm viability with seminal plasma metal levels

This study compares the semen levels of lead (Pb), cadmium (Cd), and aluminum (Al) in relation to live sperm in semen samples from 64 apparently healthy men. The measured levels were separated into live sperm count tertiles (<25% [18 subjects], 25-50% [26 subjects], and >50% [20 subjects]). The mean +/- SD for each group was calculated, and the difference between the means of the high and low tertiles were compared by ANOVA. Significant differences were observed between the high and low live sperm groups for Pb (p < 0.01) and Al (p < 0.05), but not Cd. Spearman's rank correlation between sperm viability and the semen plasma metal levels showed a direct relation to Mg (p < 0.05). However, there was an inverse relation to lead (p < 0.001), cadmium (p < 0.01), and aluminum (p < 0.01). There was no significant correlation between Ca and Zn. Linear regression between the live sperm counts and semen level of the three metals show that metal levels were inversely correlated with the percentage of live sperm (p < 0.001, < 0.01). Apparently, the presence of these metals in the environment and in seminal plasma exerts a toxic effect on sperm.

Xath5 participates in a network of bHLH genes in the developing Xenopus retina

We examined the function of basic-helix-loop-helix (bHLH) transcription factors during retinal neurogenesis. We identified Xath5, a Xenopus bHLH gene related to Drosophila atonal, which is expressed in the developing Xenopus retina. Targeted expression of Xath5 in retinal progenitor cells biased the differentiation of these cells toward a ganglion cell fate, suggesting that Xath5 can regulate the differentiation of retinal neurons. We examined the relationship between the three bHLH genes Xash3, NeuroD, and Xath5 during retinal neurogenesis and found that Xash3 is expressed in early retinoblasts, followed by coexpression of Xath5 and NeuroD in differentiating cells. We provide evidence that the expression of Xash3, NeuroD, and Xath5 is coupled and propose that these bHLH genes regulate successive stages of neuronal differentiation in the developing retina.

Cellular diversification in the vertebrate retina

The discovery of heterogeneous populations of retinal precursors with sequentially modified fates may help solve the conundrum of conserved histogenesis in the absence of determination either by birthdate or lineage. Combined with a wealth of new data on the exogenous and endogenous factors that influence cellular fate in the retina, models of how complexity is generated are beginning to emerge.

Myosin functions in Xenopus retinal ganglion cell growth cone motility in vivo

The role of myosins in Xenopus retinal ganglion cell growth cone motility in the optic tract was studied using two pharmacologic inhibitors with different specificities. 2,3-Butanedione monoxime (BDM) disrupts myosin-actin interactions of all myosins, and ML-7 specifically inhibits activation of myosin II. Both inhibitors caused growth cones to assume a collapsed morphology and decreased growth cone speed. Similar effects were observed in vitro. Interestingly, the effects of the two inhibitors, while similar, were clearly distinguishable, raising the possibility that different myosins may have different functional roles in growth cone motility. BDM caused growth cones to withdraw lamellipodia and some filopodia and eventually to freeze, whereas ML-7 caused total collapse and retraction. Concentrations of BDM and ML-7 that had no effect when applied independently stopped growth cones when applied simultaneously, suggesting that these inhibitors act synergistically on myosin function, thus providing evidence of specificity. These results imply that normal growth cone motility in the molecularly and spatially complex environment of the living brain requires myosin function.

Xenopus Brn-3.0, a POU-domain gene expressed in the developing retina and tectum. Not regulated by innervation

PURPOSE

To study the effect of denervation on the expression of the POU-domain gene Brn-3.0 in the Xenopus visual system.

METHODS

An oligonucleotide probe was used to identify homologs of the murine gene Brn-3.0 in the retina. In situ hybridization was used to determine the spatial distribution of the mRNA within the developing embryo. To study the effects of denervation on Brn-3.0 expression and cell fate, embryonic eyes were transplanted to an ectopic location on the animal (the flank) before the onset of retinal ganglion cell (RGC) axonogenesis. Gene expression in ectopic eyes and denervated tecta was analyzed over time using in situ hybridization.

RESULTS

The deduced, partial amino acid sequence for Xenopus Brn-3.0 shows 100% identity with the mouse Brn-3.0 and the human Brn-3a gene products. It is expressed during early embryonic development in distinct populations of the neural crest and later in specific cranial ganglia. It also is expressed in RGCs and in the optic tectum, beginning before the first RGC axons have reached the tectum and continuing without interruption throughout the period when retino-tectal connections are established and refined. If the retino-tectal projection is kept from forming by transplanting one eye to an ectopic location, Brn-3.0 expression is unaffected in both the ectopic eye and the denervated side of the tectum.

CONCLUSIONS

Coordinate expression of Brn-3.0 in afferent and efferent pathways suggests mutual regulation. However, the authors' evidence shows that expression in the retina is not regulated by target-derived factors nor is expression in the tectum regulated by retinal innervation.

Regulation of neuronal diversity in the Xenopus retina by Delta signalling

To generate the variety of mature neurons and glia found in the developing retina, the competence of pluripotent progenitor cells to respond to extracellular signals must be controlled. Delta, a ligand of the Notch receptor, is a candidate for regulating progenitor competence on the grounds that activation of the pathway involving Notch and Delta can inhibit cellular differentiation. Here we test this possibility in the developing Xenopus retina by misexpression of Delta messenger RNA. We find that Delta-misexpressing cells with wild-type neighbours adopt earlier fates, primarily becoming ganglion cells and cone photoreceptors. Progenitors transfected with Delta later in development also produce rod photoreceptors, but not the latest-generated cell types, demonstrating the importance of timing in Delta function. We conclude that Delta signalling in the vertebrate retina is a basic regulatory mechanism that can be used to generate neuronal diversity.

Xenopus Pax-6 and retinal development

We have cloned a homolog of Pax-6 in Xenopus laevis. Its deduced amino acid sequence has a 95% overall identity with Pax-6 homologs in other vertebrates. It is expressed early in development in cells fated to form the eye and parts of the forebrain, hindbrain, and spinal cord. It has two phases of expression in the eye. In the early phase, from stage 12.5 to stage 33/34, Xenopus Pax-6 is expressed throughout the developing retina. In the late phase, after stage 33/34, it is excluded from mature cells in the outer half of the retina and from cells in the ciliary marginal zone, remaining only in amacrine and ganglion cells. Misexpression of Pax-6 early in development results in axial defects, but no specific eye phenotype is observed. Targeted misexpression in the retina at later stages does not result in any significant bias toward formation of amacrine or ganglion cells or away from photoreceptors. Ectopic expression of the proneural gene NeuroD alters the pattern of Pax-6, substantially reducing its expression in the eye field and later reducing or eliminating the eye itself. Our results show that Pax-6 expression appears to be necessary, but not sufficient, for eye formation in Xenopus.

Engrailed and retinotectal topography

We examine the role of the Engrailed homeobox gene in establishment of local tectal topography. In the mesencephalon, a gradient of Engrailed appears early and defines the rostrocaudal axis of the tectum. Various experiments that cause ectopic Engrailed expression cause predictable readjustments of the retinotectal map. The newly discovered 'realisators' of the retinotopic map, such as receptor tyrosine kinase ligands ELF-1 and RAGS could be controlled directly by Engrailed. Indeed, recent results show that Engrailed regulates the expression of these ligands. The Engrailed gradient itself appears to be set up by signals including FGF8 and WNTI, allowing us to begin to trace the molecular cascade that is responsible for the correct wiring of the visual projection back into the early embryo.

Youth risk behavior surveillance--United States, 1995

Priority health-risk behaviors that contribute to the leading causes of mortality, morbidity, and social problems among youth and adults often are established during youth, extend into adulthood, and are interrelated. The Youth Risk Behavior Surveillance System (YRBSS) monitors six categories of priority health-risk behaviors among youth and young adults: behaviors that contribute to unintentional and intentional injuries, tobacco use, alcohol and other drug use, sexual behaviors, unhealthy dietary behaviors, and physical inactivity. The YRBSS includes both a national school-based survey conducted by CDC and state and local school-based surveys conducted by state and local education agencies. This report summarizes results from the national survey, 35 state surveys, and 16 local surveys conducted among high school students from February through May 1995. In the United States, 72% of all deaths among school-age youth and young adults result from four causes: motor vehicle crashes, other unintentional injuries, homicide, and suicide. Results from the 1995 YRBSS suggest that many high school students practice behaviors that may increase their likelihood of death from these four causes: 21.7% had rarely or never used a safety belt, 38.8% had ridden with a driver who had been drinking alcohol during the 30 days preceding the survey, 20.0% had carried a weapon during the 30 days preceding the survey, 51.6% had drunk alcohol during the 30 days preceding the survey, 25.3% had used marijuana during the 30 days preceding the survey, and 8.7% had attempted suicide during the 12 months preceding the survey. Substantial morbidity and social problems among school-age youth and young adults also result from unintended pregnancies and sexually transmitted diseases, including HIV infection. YRBSS results indicate that in 1995, 53.1% of high school students had experienced sexual intercourse, 45.6% of sexually active students had not used a condom at last sexual intercourse, and 2.0% had ever injected an illegal drug. Among adults, 65% of all deaths result from three causes: heart disease, cancer, and stroke. Most of the risk behaviors associated with these causes of death are initiated during adolescence. In 1995, 34.8% of high school students had smoked cigarettes during the 30 days preceding the survey, 39.5% had eaten more than two servings of foods typically high in fat content during the day preceding the survey, and only 25.4% had attended physical education class daily. YRBSS data are being used nationwide by health and education officials to improve national, state, and local policies and programs designed to reduce risks associated with the leading causes of mortality and morbidity. YRBSS data also are being used to measure progress toward achieving 21 national health objectives and one of eight National Education Goals.

Youth Risk Behavior Surveillance--United States, 1995

PROBLEM/CONDITION

Priority health-risk behaviors that contribute to the leading causes of mortality, morbidity, and social problems among youth and adults often are established during youth, extend into adulthood, and are interrelated.

REPORTING PERIOD

February through May 1995.

DESCRIPTION OF THE SYSTEM

The Youth Risk Behavior Surveillance System (YRBSS) monitors six categories of priority health-risk behaviors among youth and young adults: behaviors that contribute to unintentional and intentional injuries, tobacco use, alcohol and other drug use, sexual behaviors, unhealthy dietary behaviors, and physical inactivity. The YRBSS includes both a national school-based survey conducted by CDC and state and local school-based surveys conducted by state and local education agencies. This report summarizes results from the national survey, 35 state surveys, and 16 local surveys conducted among high school students from February through May 1995.

RESULTS AND INTERPRETATION

In the United States, 72% of all deaths among school-age youth and young adults result from four causes: motor vehicle crashes, other unintentional injuries, homicide, and suicide. Results from the 1995 YRBSS suggest that many high school students practice behaviors that may increase their likelihood of death from these four causes: 21.7% had rarely or never used a safety belt, 38.8% had ridden with a driver who had been drinking alcohol during the 30 days preceding the survey, 20.0% had carried a weapon during the 30 days preceding the survey, 51.6% had drunk alcohol during the 30 days preceding the survey, 25.3% had used marijuana during the 30 days preceding the survey, and 8.7% had attempted suicide during the 12 months preceding the survey. Substantial morbidity and social problems among school-age youth and young adults also result from unintended pregnancies and sexually transmitted diseases, including human immunodeficiency virus infection. YRBSS results indicate that in 1995, 53.1% of high school students had had sexual intercourse, 45.6% of sexually active students had not used a condom at last sexual intercourse, and 2.0% had ever injected an illegal drug. Among adults, 65% of all deaths result from three causes: heart disease, cancer and stroke. Most of the risk behaviors associated with these causes of death are initiated during adolescence. In 1995, 34.8% of high school students had smoked cigarettes during the 30 days preceding the survey, 39.5% had eaten more than two servings of foods typically high in fat content during the day preceding the survey, and only 25.4% had attended physical education class daily.

ACTIONS TAKEN

YRBSS data are being used nationwide by health and education officials to improve national, state, and local policies and programs designed to reduce risks associated with the leading causes of mortality and morbidity. YRBSS data also are being used to measure progress toward achieving 21 national health objectives and one of eight National Education Goals.

Engrailed, retinotectal targeting, and axonal patterning in the midbrain during Xenopus development: an antisense study

Axonal tracts in the vertebrate brain seem to respect domains of homeobox gene expression. To test the role of engrailed in tract formation in the midbrain, we inhibited its expression using antisense (AS) oligonucleotides. Phosphorothioate-modified AS oligos caused navigational errors in both the optic projection (OP) and the intertectal commissure (ITC). These oligos, however, also inhibited bFGF binding to the brain. To determine whether these tract phenotypes were due to inhibition of bFGF function or engrailed expression, we used partially phosphorothioate-modified (pp) oligos, which inhibit engrailed expression but do not affect bFGF binding. These ppAS oligos caused the ITC phenotype but had no effect on the OP. Thus, interference with bFGF function correlates with the OP phenotype, while the ITC phenotype is directly related to engrailed expression.

Signal transduction in vertebrate growth cones navigating in vivo

Navigating growth cones need signal transduction machinery to amplify and transmit the effects of extracellular signals throughout the growth cone. In culture, many drugs that affect second messengers are known to modulate neurite extension (with different effects on different neurons), and gradients of calcium influx and cyclic nucleotide analogs can cause growth cones to turn. However, it is not clear which of these responses are physiologically relevant, as axons grow through much more complex environments in vivo. The "exposed brain" preparation in Xenopus embryos provides an experimentally tractable system in which it is possible to study growth, pathfinding, and target recognition of retinal growth cones in vivo, while pharmacologically manipulating their signal transduction systems. These growth cones can also be easily studied in explant culture. We describe preliminary results of parallel in vivo and in vitro experiments using an array of drugs that perturb transduction molecules. Surprisingly, calcium ionophores and cyclic nucleotide analogs have no significant effect on retinal axon growth or pathfinding. Several agents including herbimycin A, ML-7, mastoparan, and RHC80267 inhibit retinal axon growth, both in vivo and in vitro, suggesting that tyrosine kinases, myosin, heterotrimeric G-proteins, and diacylglycerol lipase are important for retinal growth cones navigating in the optic pathway.