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Biomedical subjects

K Brose

Publications and source records attributed to K Brose.

15 recordsLinked to original sources
PubMed2001

Diversity and specificity of actions of Slit2 proteolytic fragments in axon guidance.

The Slits are secreted proteins that bind to Robo receptors and play a role in axon guidance and neuronal migration. In vertebrates, Slit2 is a major chemorepellent for developing axons and is involved in the control of midline crossing. In vivo, Slit2 is cleaved into 140 kDa N-terminal (Slit2-N) and 55-60 kDa C-terminal (Slit2-C) fragments, although the uncleaved/full-length form can also be isolated from brain extract. We explored the functional activities of Slit2 fragments by engineering mutant and truncated versions of Slit2 representing the N-, C-, and full/uncleavable (Slit2-U) fragments. Only Slit2-N and Slit2-U bind the Robo proteins. We found that in collagen gel, olfactory bulb (OB) but not dorsal root ganglia (DRG) axons are repelled by Slit2-N and Slit2-U. Moreover, only Slit2-N membranes or purified protein-induced OB growth cones collapse. Finally, we found that only recombinant Slit2-N could induce branching of DRG axons and that this effect was antagonized by Slit2-U. Therefore, different axons have distinct responses to Slit2 fragments, and these proteins have different growth-promoting capacities.

Alkaline Phosphatase↗
PubMed2001

Sensory axon response to substrate-bound Slit2 is modulated by laminin and cyclic GMP.

In vertebrates, Slit2 is a chemorepellent for some developing axons but stimulates axonal elongation and branching of sensory axons. In vivo, Slit2 is cleaved into 140-kDa N-terminal (Slit2-N) and 55- to 60-kDa C-terminal fragments, but the uncleaved/full-length form can also be isolated from brain extracts. As Slit2-N and full-length Slit2 bind tightly to cell membranes, we decided to explore the response of rat dorsal root ganglia (DRG) axons to substrate-bound Slit2 fragments in the stripe assay. Slit2 fragments were avoided by DRG axons when expressed on membranes or coated as stripes on laminin. However, when the Slit2 stripes were coated on fibronectin, DRG axons still avoided full-length Slit2 but grew preferentially on Slit2-N. DRG axon response to Slit2 fragments could be modulated by cGMP and by a laminin-1 peptide. These results strongly support the idea that extracellular matrix proteins modulate the response of growth cones to chemotropic molecules by modulating cyclic nucleotide levels.

Age Factors↗
PubMed2000

Retinal ganglion cell axon guidance in the mouse optic chiasm: expression and function of robos and slits.

The ventral midline of the nervous system is an important choice point at which growing axons decide whether to cross and project contralaterally or remain on the same side of the brain. In Drosophila, the decision to cross or avoid the CNS midline is controlled, at least in part, by the Roundabout (Robo) receptor on the axons and its ligand, Slit, an inhibitory extracellular matrix molecule secreted by the midline glia. Vertebrate homologs of these molecules have been cloned and have also been implicated in regulating axon guidance. Using in situ hybridization, we have determined the expression patterns of robo1,2 and slit1,2,3 in the mouse retina and in the region of the developing optic chiasm, a ventral midline structure in which retinal ganglion cell (RGC) axons diverge to either side of the brain. The receptors and ligands are expressed at the appropriate time and place, in both the retina and the ventral diencephalon, to be able to influence RGC axon guidance. In vitro, slit2 is inhibitory to RGC axons, with outgrowth of both ipsilaterally and contralaterally projecting axons being strongly affected. Overall, these results indicate that Robos and Slits alone do not directly control RGC axon divergence at the optic chiasm and may additionally function as a general inhibitory guidance system involved in determining the relative position of the optic chiasm at the ventral midline of the developing hypothalamus.

Animals↗
PubMed2000

Slit inhibition of retinal axon growth and its role in retinal axon pathfinding and innervation patterns in the diencephalon.

We have analyzed the role of the Slit family of repellent axon guidance molecules in the patterning of the axonal projections of retinal ganglion cells (RGCs) within the embryonic rat diencephalon and whether the slits can account for a repellent activity for retinal axons released by hypothalamus and epithalamus. At the time RGC axons extend over the diencephalon, slit1 and slit2 are expressed in hypothalamus and epithalamus but not in the lateral part of dorsal thalamus, a retinal target. slit3 expression is low or undetectable. The Slit receptors robo2, and to a limited extent robo1, are expressed in the RGC layer, as are slit1 and slit2. In collagen gels, axon outgrowth from rat retinal explants is biased away from slit2-transfected 293T cells, and the number and length of axons are decreased on the explant side facing the cells. In addition, in the presence of Slit2, overall axon outgrowth is decreased, and bundles of retinal axons are more tightly fasciculated. This action of Slit2 as a growth inhibitor of retinal axons and the expression patterns of slit1 and slit2 correlate with the fasciculation and innervation patterns of RGC axons within the diencephalon and implicate the Slits as components of the axon repellent activity associated with the hypothalamus and epithalamus. Our findings suggest that in vivo the Slits control RGC axon pathfinding and targeting within the diencephalon by regulating their fasciculation, preventing them or their branches from invading nontarget tissues, and steering them toward their most distal target, the superior colliculus.

Animals↗
PubMed2000

Slit proteins: key regulators of axon guidance, axonal branching, and cell migration.

In the past year, Slit proteins have been identified as important regulators of axon guidance and cell migration in Drosophila and vertebrates. Remarkably, they were simultaneously identified as negative regulators, repelling various axonal and cell migrations in both invertebrates and vertebrates, and as positive regulators, stimulating branching and extension of at least one class of axons in vertebrates.

Animals↗
PubMed1999

Biochemical purification of a mammalian slit protein as a positive regulator of sensory axon elongation and branching.

Many neurons in both vertebrates and invertebrates innervate multiple targets by sprouting secondary axon collaterals (or branches) from a primary axon shaft. To begin to identify molecular regulators of axon branch initiation or extension, we studied the growth of single sensory axons in an in vitro collagen assay system and identified an activity in extracts of embryonic spinal cord and of postnatal and adult brain that promotes the elongation and formation of extensive branches by these axons. Biochemical purification of the activity from calf brain extracts led to the identification of an amino-terminal fragment of Slit2 as the main active component and to the discovery of a distinct activity that potentiates its effects. These results indicate that Slit proteins may function as positive regulators of axon collateral formation during the establishment or remodeling of neural circuits.

Amino Acid Sequence↗
PubMed1999

Slit proteins bind Robo receptors and have an evolutionarily conserved role in repulsive axon guidance.

Extending axons in the developing nervous system are guided in part by repulsive cues. Genetic analysis in Drosophila, reported in a companion to this paper, identifies the Slit protein as a candidate ligand for the repulsive guidance receptor Roundabout (Robo). Here we describe the characterization of three mammalian Slit homologs and show that the Drosophila Slit protein and at least one of the mammalian Slit proteins, Slit2, are proteolytically processed and show specific, high-affinity binding to Robo proteins. Furthermore, recombinant Slit2 can repel embryonic spinal motor axons in cell culture. These results support the hypothesis that Slit proteins have an evolutionarily conserved role in axon guidance as repulsive ligands for Robo receptors.

Amino Acid Sequence↗
PubMed1999

Slit2-Mediated chemorepulsion and collapse of developing forebrain axons.

Diffusible chemorepellents play a major role in guiding developing axons toward their correct targets by preventing them from entering or steering them away from certain regions. Genetic studies in Drosophila revealed a novel repulsive guidance system that prevents inappropriate axons from crossing the CNS midline; this repulsive system is mediated by the Roundabout (Robo) receptor and its secreted ligand Slit. In rodents, Robo and Slit are expressed in the spinal cord and Slit can repel spinal motor axons in vitro. Here, we extend these findings into higher brain centers by showing that Robo1 and Robo2, as well as Slit1 and Slit2, are often expressed in complementary patterns in the developing forebrain. Furthermore, we show that human Slit2 can repel olfactory and hippocampal axons and collapse their growth cones.

Animals↗
PubMed1998

Roundabout controls axon crossing of the CNS midline and defines a novel subfamily of evolutionarily conserved guidance receptors.

The robo gene in Drosophila was identified in a large-scale mutant screen for genes that control the decision by axons to cross the CNS midline. In robo mutants, too many axons cross and recross the midline. Here we show that robo encodes an axon guidance receptor that defines a novel subfamily of immunoglobulin superfamily proteins that is highly conserved from fruit flies to mammals. For those axons that never cross the midline, Robo is expressed on their growth cones from the outset; for the majority of axons that do cross the midline, Robo is expressed at high levels on their growth cones only after they cross the midline. Transgenic rescue experiments reveal that Robo can function in a cell-autonomous fashion. Robo appears to function as the gatekeeper controlling midline crossing.

Amino Acid Sequence↗
PubMed1996

Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo.

Hematopoietic stem cells (HSC) are multipotent cells that reside in the bone marrow and replenish all adult hematopoietic lineages throughout the lifetime of the animal. While experimenting with staining of murine bone marrow cells with the vital dye, Hoechst 33342, we discovered that display of Hoechst fluorescence simultaneously at two emission wavelengths revealed a small and distinct subset of whole bone marrow cells that had phenotypic markers of multipotential HSC. These cells were shown in competitive repopulation experiments to contain the vast majority of HSC activity from murine bone marrow and to be enriched at least 1,000-fold for in vivo reconstitution activity. Further, these Hoechst-stained side population (SP) cells were shown to protect recipients from lethal irradiation at low cell doses, and to contribute to both lymphoid and myeloid lineages. The formation of the Hoechst SP profile was blocked when staining was performed in the presence of verapamil, indicating that the distinctly low staining pattern of the SP cells is due to a multidrug resistance protein (mdr) or mdr-like mediated efflux of the dye from HSC. The ability to block the Hoechst efflux activity also allowed us to use Hoechst to determine the DNA content of the SP cells. Between 1 and 3% of the HSC were shown to be in S-G2M. This also enabled the purification of the G0-G1 and S-G2M HSC had a reconstitution capacity equivalent to quiescent stem cells. These findings have implications for models of hematopoietic cell development and for the development of genetic therapies for diseases involving hematopoietic cells.

Animals↗
PubMed1996

Hepatocyte growth factor/scatter factor is an axonal chemoattractant and a neurotrophic factor for spinal motor neurons.

In the embryonic nervous system, developing axons can be guided to their targets by diffusible factors secreted by their intermediate and final cellular targets. To date only one family of chemoattractants for developing axons has been identified. Grafting and ablation experiments in fish, amphibians, and birds have suggested that spinal motor axons are guided to their targets in the limb in part by a succession of chemoattractants made by the sclerotome and by the limb mesenchyme, two intermediate targets that these axons encounter en route to their target muscles. Here we identify the limb mesenchyme-derived chemoattractant as hepatocyte growth factor/scatter factor (HGF/SF), a diffusible ligand for the c-Met receptor tyrosine kinase, and we also implicate HGF/SF at later stages as a muscle-derived survival factor for motoneurons. These results indicate that, in addition to functioning as a mitogen, a motogen, and a morphogen in nonneural systems, HGF/SF can function as a guidance and survival factor in the developing nervous system.

Animals↗
PubMed1995

Effects of retroviral vector design on expression of human adenosine deaminase in murine bone marrow transplant recipients engrafted with genetically modified cells.

To determine which features of retroviral vector design most critically affect gene expression in hematopoietic cells in vivo, we have constructed a variety of different retroviral vectors which encode the same gene product, human adenosine deaminase (EC 3.5.4.4), and possess the same vector backbone yet differ specifically in transcriptional control sequences suggested by others to be important for gene expression in vivo. Murine bone marrow cells were transduced by each of the recombinant viruses and subsequently used to reconstitute the hematopoietic system of lethally irradiated recipients. Five to seven months after transplantation, analysis of the peripheral blood of animals transplanted with cells transduced by vectors which employ viral long terminal repeats (LTRs) for gene expression indicated that in 83% (77/93) of these animals, the level of human enzyme was equal to or greater than the level of endogenous murine enzyme. Even in bone marrow transplant recipients reconstituted for over 1 year, significant levels of gene expression were observed for each of the vectors in their bone marrow, spleen, macrophages, and B and T lymphocytes. However, derivatives of the parental MFG-ADA vector which possess either a single base mutation (termed B2 mutation) or myeloproliferative sarcoma virus LTRs rather than the Moloney murine leukemia virus LTRs led to significantly improved gene expression in all lineages. These studies indicate that retroviral vectors which employ viral LTRs for the expression of inserted sequences make it possible to obtain high levels of a desired gene product in most hematopoietic cell lineages for close to the lifetime of bone marrow transplant recipients.

Adenosine Deaminase↗
PubMed1993

Vaccination with irradiated tumor cells engineered to secrete murine granulocyte-macrophage colony-stimulating factor stimulates potent, specific, and long-lasting anti-tumor immunity.

To compare the ability of different cytokines and other molecules to enhance the immunogenicity of tumor cells, we generated 10 retroviruses encoding potential immunomodulators and studied the vaccination properties of murine tumor cells transduced by the viruses. Using a B16 melanoma model, in which irradiated tumor cells alone do not stimulate significant anti-tumor immunity, we found that irradiated tumor cells expressing murine granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulated potent, long-lasting, and specific anti-tumor immunity, requiring both CD4+ and CD8+ cells. Irradiated cells expressing interleukins 4 and 6 also stimulated detectable, but weaker, activity. In contrast to the B16 system, we found that in a number of other tumor models, the levels of anti-tumor immunity reported previously in cytokine gene transfer studies involving live, transduced cells could be achieved through the use of irradiated cells alone. Nevertheless, manipulation of the vaccine or challenge doses made it possible to demonstrate the activity of murine GM-CSF in those systems as well. Overall, our results have important implications for the clinical use of genetically modified tumor cells as therapeutic cancer vaccines.

Animals↗