PubMed Health⌕ Search

Biomedical subjects

C Seaman

Publications and source records attributed to C Seaman.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of neogenin-expressing neural progenitor populations and migrating neuroblasts in the embryonic mouse forebrain.

Many studies have demonstrated a role for netrin-1-deleted in colorectal cancer (DCC) interactions in both axon guidance and neuronal migration. Neogenin, a member of the DCC receptor family, has recently been shown to be a chemorepulsive axon guidance receptor for the repulsive guidance molecule (RGM) family of guidance cues [Rajagopalan S, Deitinghoff L, Davis D, Conrad S, Skutella T, Chedotal A, Mueller B, Strittmatter S (2004) Neogenin mediates the action of repulsive guidance molecule. Nat Cell Biol 6:755-762]. Here we show that neogenin is present on neural progenitors, including neurogenic radial glia, in the embryonic mouse forebrain suggesting that neogenin expression is a hallmark of neural progenitor populations. Neogenin-positive progenitors were isolated from embryonic day 14.5 forebrain using flow cytometry and cultured as neurospheres. Neogenin-positive progenitors gave rise to neurospheres displaying a high proliferative and neurogenic potential. In contrast, neogenin-negative forebrain cells did not produce long-term neurosphere cultures and did not possess a significant neurogenic potential. These observations argue strongly for a role for neogenin in neural progenitor biology. In addition, we also observed neogenin on parvalbumin- and calbindin-positive interneuron neuroblasts that were migrating through the medial and lateral ganglionic eminences, suggesting a role for neogenin in tangential migration. Therefore, neogenin may be a multi-functional receptor regulating both progenitor activity and neuroblast migration in the embryonic forebrain.

Animals↗
PubMed2001

Netrin-3 protein is localized to the axons of motor, sensory, and sympathetic neurons.

The netrin family of axon guidance cues has been shown to play a pivotal role in the guidance of a variety of axon projections during embryonic development, both in the vertebrate and invertebrate. While the guidance potential of netrin-1 has been examined in depth in many regions of the developing mouse brain very little information is available on the expression and activity of netrin-3. Here we show that the netrin-3 protein is present on motor neurons and subpopulations of neurons within sensory and sympathetic ganglia. Moreover, significant levels of netrin-3 protein were found to be associated with the axons projecting from these neurons suggesting a role for netrin-3 in axon pathfinding and fasciculation within the peripheral nervous system.

Animals↗
PubMed2001

Localization of the netrin guidance receptor, DCC, in the developing peripheral and enteric nervous systems.

Over recent years the secreted guidance cue, netrin-1, and its receptor, DCC, have been shown to be an essential guidance system driving axon pathfinding within the developing vertebrate central nervous system (CNS). Mice lacking DCC exhibit severe defects in commissural axon extension towards the floor plate demonstrating that the DCC-netrin guidance system is largely responsible for directing axonal projections toward the ventral midline in the developing spinal cord (Fazeli et al., Nature 386 (1997) 796). In addition, these mutants lack several major commissures within the forebrain, including the corpus callosum and the hippocampal commissure. In contrast to the CNS, the role of the DCC guidance receptor in the development of the mammalian peripheral and enteric nervous systems (PNS and ENS) has not been investigated. Here we demonstrate using immunohistochemical analysis that the DCC receptor is present in the developing mouse PNS where it is found on spinal, segmental, and sciatic nerves, and in developing sensory ganglia and their associated axonal projections. In addition, DCC is present in the ENS throughout the early developmental phase.

Animals↗
PubMed2000

DCC plays a role in navigation of forebrain axons across the ventral midbrain commissure in embryonic xenopus.

In the developing vertebrate brain, growing axons establish a scaffold of axon tracts connected across the midline via commissures. We have previously identified a population of telencephalic neurons that express NOC-2, a novel glycoform of the neural cell adhesion molecule N-CAM that is involved in axon guidance in the forebrain. These axons arise from the presumptive telencephalic nucleus, course caudally along the principal longitudinal tract of the forebrain, cross the ventral midline in the midbrain, and then project to the contralateral side of the brain. In the present study we have investigated mechanisms controlling the growth of these axons across the ventral midline of the midbrain. The axon guidance receptor DCC is expressed by the NOC-2 population of axons both within the longitudinal tract and within the ventral midbrain commissure. Disruption of DCC-dependent interactions, both in vitro and in vivo, inhibited the NOC-2 axons from crossing the ventral midbrain. Instead, these axons grew along aberrant trajectories away from the midline, suggesting that DCC-dependent interactions are important for overcoming inhibitory mechanisms within the midbrain of the embryonic vertebrate brain. Thus, coordinated responsiveness of forebrain axons to both chemostimulatory and chemorepulsive cues appears to determine whether they cross the ventral midline in the midbrain.

Animals↗
PubMed2000

Expression of the netrin-1 receptor, deleted in colorectal cancer (DCC), is largely confined to projecting neurons in the developing forebrain.

Axon guidance mechanisms are crucial to the development of an integrated nervous system. One family of molecules that may be important in establishing axonal connectivity in mammals is the Netrins, and their putative receptors DCC (deleted in colorectal cancer), Neogenin, and Unc-5. Knockout and mutational analyses of some of these genes have shown that they are critically involved in the development of several specific pathways in the developing brain. However, previous expression analyses of these genes have largely been confined to the developing spinal cord. In the present study, we analyzed the expression of DCC in the developing mouse forebrain. We found that DCC protein is expressed in specific axonal populations projecting from the developing olfactory bulb, neocortex, hippocampus, and epithalamus/habenular complex. In the developing olfactory bulb and neocortex, DCC expression is particularly evident during the targeting phase of axon outgrowth and is then rapidly downregulated. As predicted from the knockout and mutational analyses of this gene, DCC is expressed in axonal commissures, in particular the corpus callosum, hippocampal commissure, and the anterior commissure. In addition, we found that DCC is expressed in the habenular commissure, the fasciculus retroflexus, and the stria medularis. Therefore, this analysis implicates a function for DCC in additional axonal guidance systems not predicted from the knockout and mutational analyses.

Animals↗
PubMed1994

Experience with 500 prenatal diagnoses of sickle cell diseases: the effect of gestational age on affected pregnancy outcome.

Prenatal diagnosis of sickle cell diseases is obtained rapidly and precisely by polymerase chain reaction (PCR) with Ddel restriction analysis and dot-blotting with allele-specific oligonucleotides (ASO). Prenatal diagnosis of HgbSS and HgbSC was performed in 500 pregnancies, 196 by Southern blot and 304 by PCR. PCR drastically shortened the interval from sampling to reporting, allowing acceptance even of samples with unknown paternal phenotype, and resulted in an overall four-fold increase in diagnoses. In 108 pregnancies, the diagnosis was an affected fetus; 25 were HgbSC: 3 (12 per cent) were terminated; 83 were HgbSS: four ended in miscarriage; 40/79 (51 per cent) were terminated. The gestational age at the time of report to the mother appeared to be a major outcome determinant when the fetal diagnosis was HgbSS. The change-point in the maternal decision was found at 20 weeks of gestation. Before the 20th week, most mothers (64 per cent) chose termination; thereafter, the majority (72 per cent) chose continuation. The odds ratio of termination in earlier relative to later reporting was 4.7. In order to offer a choice to the mothers at risk of delivering a fetus affected by sickle cell disease, the diagnosis should be reported before the 20th week of gestation.

Amniocentesis↗
PubMed1993

Mechanism of red blood cell aging: relationship of cell density and cell age.

The human red cell has a life span of 120 days. The mechanism that determines cell removal from the circulation with such precision remains unknown. Most studies of red cell aging have been based on analysis of cells of progressively increasing age separated by density. The relationship between red cell age and density has been recently challenged, and the hypothesis has been put forward that cell death is not the result of a progressive deterioration of essential cell constituents. This theory was based on preliminary observations in transient erythroblastopenia of childhood, which could not later be confirmed. When the relationship between cell aging and increasing density is critically reviewed, it appears to be based on firm experimental evidence, confirmed by in vivo demonstration of decreasing survival of cells of increasing age. Analysis of studies using buoyant density gradients reveals that this technique can easily distinguish the single exponential slope of decline for those cell components that change progressively throughout the red cell life span from the biphasic decline of those that decrease drastically at the reticulocyte-mature red cell transition. The view that the aging of the red cell and its removal from the circulation result from a progressive series of events during the 120 days of its life span appears to be the most consistent with the available data. Density separation, validated by much experimental evidence, remains a most useful technique for the study of the mechanism of aging of the red cell.

Animals↗
PubMed1991

The mechanism of decline of age-dependent enzymes in the red blood cell.

Buoyant density centrifugation on discontinuous gradients separates red blood cells (RBCs) according to age, as shown by radiolabelling experiments both in vitro and in vivo. Changes observed in these gradients reflect in vivo rates of decline. A progressive metabolic decline may render the RBC incapable of surviving stresses in the circulation. It was hypothesized that changes only take place at the reticulocyte-mature RBC transition. RBC hexokinase (HK) has two isozymes, one predominant in reticulocytes, the other in mature RBCs. We compared its decline in the density gradient, with that of pyrimidine-5'-nucleotidase (P5N), glutamate-oxaloacetate transaminase (GOT) and pyruvate kinase (PK). The decline of HK and P5N was clearly biphasic; for GOT and PK instead there was a single slope. Thus changes taking place at the reticulocyte-RBC transition are clearly identified by a biphasic slope in the gradient. The view of a progressive metabolic decline in vivo for the RBC therefore remains valid.

5'-Nucleotidase↗
PubMed1991

Regulation of glycolysis in the erythrocyte: role of the lactate/pyruvate and NAD/NADH ratios.

Mature erythrocytes, when removed from the circulation, exhibit severe disturbances of glycolytic flow, with accumulation not only of lactate, the ultimate product of glycolysis, but also of several upstream metabolic intermediates, primarily fructose-1,6-diphosphate, glyceraldehyde-3-phosphate, and dihydroxyacetone phosphate. This accumulation may be prevented (and also reverted) by allowing the diffusible end products lactate and pyruvate to leave the cell by equilibrating with a much larger extracellular compartment. The disturbance of erythrocyte glycolysis does not result from direct inhibition by lactate itself but from the interplay between the lactate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase (3-PGAD) reactions. The accumulation of intermediates reflects the increased lactate-to-pyruvate ratio; this leads to a secondary imbalance of the nicotinamide adenine dinucleotide-to-reduced nicotinamide adenine dinucleotide (NAD-to-NADH) ratio, which in turn slows down glycolysis at the 3-PGAD step, whose upstream metabolites then pile up. No accumulation, however, takes place if the lactate-to-pyruvate ratio is maintained constant in the extracellular compartment, regardless of concentrations. These studies demonstrate that orderly glycolysis in the erythrocyte is regulated by the NAD-to-NADH ratio and also provide a method that makes possible the in vitro study of erythrocyte glycolysis.

Adult↗
PubMed1991

Randomized, placebo-controlled trial of iron supplementation in infants with low hemoglobin levels fed iron-fortified formula.

In spite of the declining prevalence of iron-deficiency anemia, a large proportion of low-income infants have "low-normal" (11-11.5 g/dL) and "low" (less than 11 g/dL) hemoglobin (Hgb) values. Because most of these infants are fed iron-fortified formulas, it was of interest whether additional iron supplementation would enhance Hgb values. A cohort of 334 healthy, inner-city, minority, 6-month-old infants, fed iron-fortified formulas, with Hgb values ranging from 9 to 11.5 g/dL, participated in a double-blind, randomized, placebo-controlled trial of supplemental iron at 0, 3, and 6 mg/kg per day for 3 months. Hemoglobin values increased significantly with age, regardless of assignment to placebo or supplemental iron (means for the entire cohort: 6 months 10.9 g/dL, 8 months 11.2, 10 months 11.3, and 12 months 11.4). The proportion of "responders" (Hgb level increased greater than or equal to 1 g/dL) was 34% and did not differ significantly by placebo or iron dose. There were no significant differences in mean corpuscular volume or levels of erythrocyte porphyrins or serum ferritin between treatment groups. The implications of this clinical trial are twofold: (1) screening healthy infants fed iron-fortified formula at the age of 6 months is not justified, regardless of socioeconomic status; (2) the clinical practice of routinely treating low-income, "low-Hgb" infants with iron supplementation, without regard to dietary considerations, is unwarranted.

Anemia, Hypochromic↗
PubMed1990

An isozyme of hexokinase specific for the human red blood cell (HKR)

The hexokinase (HK) of the human red blood cell (RBC) was separated into two distinct major isozymes by fast protein liquid chromatography using a linear salt gradient on a MonoQ column. The first isozyme (HKI) eluted as a sharp peak at the same position as HKI of human liver. The second isozyme eluted between HKI and HKII of human white blood cells, and it appeared to be unique to the RBC (it was designated HKR). From a gel filtration column, HKR eluted before HKI, suggesting that it was larger than HKI by several kilodaltons. In a mitochondria-enriched fraction from human reticulocytes, no HKR was found; thus, HKR was not a mitochondrial enzyme. Despite these differences in chromatographic behavior, size, and mitochondrial binding, both forms behaved kinetically as HKI. RBC from normal blood contained HKI and HKR at an equal activity, but in reticulocyte-rich RBC, HKR dominated. When RBC of increasing age was separated by buoyant density ultracentrifugation, the total HK activity decayed in a biphasic manner, with half-lives respectively of approximately 15 and approximately 51 days. When isolated by MonoQ column from each age-separated fraction, HKR was the major form in the youngest RBC, and decreased rapidly with cell age, with a t 1/2 of approximately 10 days, representing a negligible activity in the oldest RBC. Instead, HKI was relatively stable through the entire life span of the RBC, with a t 1/2 of approximately 66 days. Thus, HKR appears to be an RBC-specific isozyme that is predominant in the reticulocyte and is then rapidly degraded. During maturation of the RBC, the fast decay of HKR contributes to the early sharp decline of HK activity and the slow decay of HKI to the later gradual decline.

Animals↗
PubMed1990

Planning an exchange transfusion in patients with sickle cell syndromes.

Partial exchange transfusions are performed in sickle cell patients for a variety of reasons. An algorithm to plan a nonautomated exchange in patients with sickle cell syndromes was developed and validated by a study of 40 such procedures. Formulas that can be used to explore alternatives, by assessing at any point during the exchange the current concentration of sickleable cells and the hematocrit, were devised: a computer program in BASIC is available for maximum versatility. The two most important determinants of the exchange are the patient's initial hematocrit and the desired final concentration of sickleable cells; the rate and type of exchange (continuous or discontinuous) are not important. The final hematocrit depends on the type of blood product used. An exchange can be performed with packed red blood cells (PRBC), whole blood (or its equivalent, PRBC reconstituted with albumin), or it can be started with PRBC and continued with whole blood. Whole blood decreases the concentration of sickeleable cells rapidly and increases the hematocrit slowly; it does not markedly increase the viscosity. PRBCs decrease the concentration of sickleable cells more slowly and increase the hematocrit faster; thus, they may increase the blood viscosity to dangerous levels.

Algorithms↗
PubMed1987

Cardiorespiratory response to exercise in patients with thalassemia major.

The cardiorespiratory response to exercise was examined in 13 patients, 12 to 22 yr of age, who were in stable condition while receiving regular transfusions for thalassemia major. Before transfusion (Hgb, 10.8 g/dl), the patients had reduced peak oxygen consumption for body weight (by 25%, p less than 0.002) in comparison with 20 age- and sex-matched control subjects (Hgb, 13.8 g/dl). The ventilatory equivalent for carbon dioxide was significantly reduced at all work rates, and end-tidal PCO2 was abnormally high (46.3 versus 40.7 mm Hg, p less than 0.001), but ventilatory reserve, as estimated from pulmonary function tests, was normal. Both heart rate and cardiac output (as estimated by the indirect Fick method) were abnormally high during exercise; at an oxygen consumption of 19 ml/min/kg, heart rate was 13% higher (p less than 0.01) and, at 16 ml/min/kg, cardiac output was 28% higher (p less than 0.001) in the patients than in the control subjects. Nine patients were retested 3 to 8 days after transfusion (Hgb, 13.0 g/dl, p50, 26.4 mm Hg). Neither ventilatory nor circulatory abnormalities improved significantly. In patients 12 to 22 yr of age in stable condition with thalassemia major, we conclude: cardiac output, estimated by the CO2 rebreathing method, is high and arteriovenous O2 extraction is low during exercise; the high cardiac output during exercise is associated with hypoventilation; the high cardiac output is independent of short-term changes in hemoglobin concentration associated with transfusion.

2,3-Diphosphoglycerate↗