Biomedical subjects

Flavio Keller

Publications and source records attributed to Flavio Keller.

9 recordsLinked to original sources

PubMed2006

A 3D model of Reelin subrepeat regions predicts Reelin binding to carbohydrates.

Reelin is a large molecule of the extracellular matrix (ECM) which regulates neuronal positioning during the early stages of cortical development in vertebrate species. The Reelin molecule can be subdivided into a smaller N-terminal domain, showing homology with F-spondin, and a larger C-terminal region containing 8 EGF-like repeats. The localization of Reelin in the ECM, its large dimensions and the modular organization of its primary structure led us to suppose a structure of its modules similar to domains commonly found in ECM proteins such as Agrin, laminins and thrombospondins. We therefore performed a sequence alignment and molecular modeling analysis to study the three-dimensional fold of the Reelin subrepeat regions. Our analysis produces a tentative model of the core region of the Reelin subrepeat sequences and suggests the presence in this 3D model of structural features common to polysaccharide-binding modules which are often found on proteoglycans of the ECM. These findings provide a conceptual framework for further experiments aimed at testing the functions of the EGF-like repeat regions of Reelin.

Amino Acid Sequence↗

PubMed2006

Paradoxical effects of prenatal acetylcholinesterase blockade on neuro-behavioral development and drug-induced stereotypies in reeler mutant mice.

INTRODUCTION: Epidemiological and experimental studies support a link between genetic and epigenetic factors in vulnerability to develop enduring neurobehavioral alterations. We studied the interplay between genetic vulnerability and the prenatal exposure to a neurotoxic compound. Chlorpyrifos, a potent and reversible acetylcholinesterase blocker used as a pesticide, and the "reeler" mouse, lacking the extracellular-matrix protein Reelin, were used. MATERIALS AND METHODS: Homozygous reeler (RL), heterozygous (HZ), and wild-type (WT) mice were prenatally exposed to chlorpyrifos-oxon (CPF-O), the active metabolite of chlorpyrifos, or to vehicle (prenatal controls) on gestation days 14-16, that is, during a peak period of neurogenesis in the cerebral cortex. The offspring was reared by the natural dam and tested during infancy and at adulthood for global consequences of the prenatal exposure. CONCLUSION: The results are consistent with complex interactions between genetic (reeler genotype) and epigenetic (prenatal exposure to CPF-O) factors. In the case of some "genetically modulated" parameters (ultrasound vocalization, amphetamine-induced locomotion, and stereotypy), exposure to CPF-O paradoxically reverted the effects produced by progressive reelin absence. Conversely, for an "epigenetically modulated" parameter (grasping reflex maturation), the effects of CPF-O exposure were counteracted by progressive reelin absence. Finally, for parameters apparently untouched by either factor alone (righting reflex latency, scopolamine-induced locomotor activity), prenatal CPF-O exposure unmasked an otherwise latent genotype dependency. This complex picture also points to reciprocal adaptations within cholinergic and dopaminergic systems during development. Data are interesting in view of recently discovered cholinergic abnormalities in autism and schizophrenia, and may suggest new avenues for early intervention.

Amphetamine↗

PubMed2006

Reelin is transiently expressed in the peripheral nerve during development and is upregulated following nerve crush.

Reelin is an extracellular matrix protein which is critical for the positioning of migrating post-mitotic neurons and the laminar organization of several brain structures during development. We investigated the expression and localization of Reelin in the rodent peripheral nerve during postnatal development and following crush injury in the adult stage. As shown with Western blotting, immunocytochemistry and RT-PCR, Schwann cells in the developing peripheral nerve and in primary cultures from neonatal nerves produce and secrete Reelin. While Reelin levels are downregulated in adult stages, they are again induced following sciatic nerve injury. A morphometric analysis of sciatic nerve sections of reeler mice suggests that Reelin is not essential for axonal ensheathment by Schwann cells, however, it influences the caliber of myelinated axons and the absolute number of fibers per unit area. This indicates that Reelin may play a role in peripheral nervous system development and repair by regulating Schwann cell-axon interactions.

Animals↗

PubMed2004

Retraction.

Explore the source record for details and available documents.

Retraction Notice↗

PubMed2003

Methodological factors influencing measurement and processing of plasma reelin in humans.

BACKGROUND: Reelin, intensively studied as an extracellular protein that regulates brain development, is also expressed in a variety of tissues and a circulating pool of reelin exists in adult mammals. Here we describe the methodological and biological foundation for carrying out and interpreting clinical studies of plasma reelin. RESULTS: Reelin in human plasma was sensitive to proteolysis, freeze-thawing and heating during long-term storage, sample preparation and electrophoresis. Reelin in plasma was a dimer under denaturing conditions. Boiling of samples resulted in laddering, suggesting that each of the 8 repeats expressed in reelin contains a heat-labile covalent bond susceptible to breakage. Urinary-type and tissue-type plasminogen activator converted reelin to a discrete 310 kDa fragment co-migrating with the major immunoreactive reelin fragment seen in plasma and also detected in brain. (In contrast, plasmin produced a spectrum of smaller unstable reelin fragments.) We examined archival plasma of 10 pairs of age-matched male individuals differing in repeat length of a CGG repeat polymorphism of the 5'-untranslated region of the reelin gene (both alleles < 11 repeats vs. one allele having >11 repeats). Reelin 310 kDa band content was lower in subjects having the long repeats in all 10 pairs, by 25% on average (p < 0.001). In contrast, no difference was noted for amyloid precursor protein. CONCLUSIONS: Our studies indicate the need for caution in measuring reelin in archival blood samples, and suggest that assays of plasma reelin should take into account three dimensions that might vary independently: a) the total amount of reelin protein; b) the relative amounts of reelin vs. its proteolytic processing products; and c) the aggregation state of the native protein. Reelin-plasminogen activator interactions may affect their roles in synaptic plasticity. Our results also suggest that the human CGG repeat polymorphism affects reelin gene expression, and may affect susceptibility to human disease.

Blotting, Western↗

PubMed2003

RETRACTED: Reelin promotes peripheral synapse elimination and maturation.

Reelin is an extracellular protein that is crucial for layer formation in the embryonic brain. Here, we demonstrate that Reelin functions postnatally to regulate the development of the neuromuscular junction. Reelin is required for motor end-plate maturation and proper nerve-muscle connectivity, and it directly promotes synapse elimination. Unlike layer formation, neuromuscular junction development requires a function of Reelin that is not mediated by Disabled1 or very-low-density lipoprotein receptors and apolipoprotein E receptor 2 receptors but by a distinct mechanism involving its protease activity.

Action Potentials↗

PubMed2003

Reduced programmed cell death in brains of serotonin transporter knockout mice.

Serotonin (5-HT) is known to reduce apoptosis and in rodent models of brain ischemia. Modulation of programmed cell death during neural development was assessed in early postnatal brains of serotonin transporter (5-HTT) knockout mice, characterized by elevated extracellular 5-HT levels. The number of apoptotic cells visualized at postnatal day-1 (P1) by ISEL+ or TUNEL staining was significantly reduced in the striatum, thalamus/hypothalamus, cerebral cortex and hippocampus of 5-HTT knockout mice, compared to wild type and heterozygote mice, with differences displaying an increasing fronto-caudal gradient and regional specificity. These findings underscore 5-HT roles in the regulation of programmed cell death during brain development, and spur interest into pharmacological interventions aimed at relieving pathological apoptosis by potentiating serotoninergic neurotransmission.

Animals↗

PubMed2003

The neurobiological context of autism.

Autistic disorder (AD) is a complex neuropsychiatric disorder of neurodevelopmental origin, where multiple genetic and environmental factors may interact, resulting in a clinical continuum. The genetic component is best described by a multilocus model that takes into account epistatic interactions between several susceptibility genes. In the past ten years enormous progress has been made in identifying chromosomal regions in linkage with AD, but moving from chromosomal regions to candidate genes has proven to be tremendously difficult. Neuroanatomical findings point to early dysgenetic events taking place in the cerebral cortex, cerebellum, and brainstem. At the cellular level, disease mechanisms may include altered cell migration, increased cell proliferation, decreased cell death, or altered synapse elimination. Neurochemical findings in AD point to involvement of multiple neurotransmitter systems. The serotoninergic system has been intensively investigated in AD, but other neurotransmitter systems (e.g., the GABAergic and the cholinergic system) are also coming under closer scrutiny. The role of environmental factors is still poorly characterized. It is not clear yet whether environmental factors act merely as precipitating agents, always requiring an underlying genetic liability, or whether they represent an essential component of a pathogenetic process where genetic liability alone does not lead to the full-blown autism phenotype. A third potential player in the pathogenesis of autism, in addition to genetic and environmental factors, is developmental variability due to "random" factors, e.g. small fluctuations of gene expression and complex, non-deterministic interactions between genes during brain development. These considerations suggest that a non-deterministic conceptual framework is highly appropriate for autism research.

Animals↗

PubMed2001

Reelin is a serine protease of the extracellular matrix.

Reelin is an extracellular matrix protein that plays a pivotal role in development of the central nervous system. Reelin is also expressed in the adult brain, notably in the cerebral cortex, where it might play a role in synaptic plasticity. The mechanism of action of reelin at the molecular level has been the subject of several hypotheses. Here we show that reelin is a serine protease and that proteolytic activity is relevant to its function, since (i) Reelin expression in HEK 293T cells impairs their ability to adhere to fibronectin-coated surfaces, and adhesion to fibronectin is restored by micromolar concentrations of diisopropyl phosphorofluoridate, a serine hydrolase inhibitor; (ii) purified Reelin binds FP-Peg-biotin, a trap probe which irreversibly binds to serine residues located in active catalytic sites of serine hydrolases; (iii) purified Reelin rapidly degrades fibronectin and laminin, while collagen IV is degraded at a much slower rate; fibronectin degradation is inhibited by inhibitors of serine proteases, and by monoclonal antibody CR-50, an antibody known to block the function of Reelin both in vitro and in vivo. The proteolytic activity of Reelin on adhesion molecules of the extracellular matrix and/or receptors on neurons may explain how Reelin regulates neuronal migration and synaptic plasticity.

Cell Adhesion↗