Papers by Matthias Gesemann
Human Molecular Genetics, 2020
The molecular cause of the majority of rare autosomal recessive disorders remains unknown. Consan... more The molecular cause of the majority of rare autosomal recessive disorders remains unknown. Consanguinity due to extensive homozygosity unravels many recessive phenotypes and facilitates the detection of novel gene-disease links. Here, we report two siblings with phenotypic signs, including intellectual disability (ID), developmental delay and microcephaly from a Pakistani consanguineous family in which we have identified homozygosity for p(Tyr103His) in the PSMB1 gene (Genbank NM_002793) that segregated with the disease phenotype. PSMB1 encodes a β-type proteasome subunit (i.e. β6). Modeling of the p(Tyr103His) variant indicates that this variant weakens the interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits and thus destabilizes the 20S proteasome complex. Biochemical experiments in human SHSY5Y cells revealed that the p(Tyr103His) variant affects both the processing of PSMB1/β6 and its incorporation into proteasome, thus impairing proteasome activity. CRISPR/Cas9 mutag...
Molecular and Cellular Neuroscience, Feb 1, 2004
We recently used a differential display PCR screen to identify secreted and transmembrane protein... more We recently used a differential display PCR screen to identify secreted and transmembrane proteins that are highly expressed in the developing rat basilar pons, a prominent ventral hindbrain nucleus used as a model for studies of neuronal migration, axon outgrowth, and axon-target recognition. Here we describe cloning and characterization of one of these molecules, now called MDGA1, and a closely related homologue, MDGA2. Analyses of the full-length coding region of MDGA1 and MDGA2 indicate that they encode proteins that comprise a novel subgroup of the Ig superfamily and have a unique structural organization consisting of six immunoglobulin (Ig)-like domains followed by a single MAM domain. Biochemical characterization demonstrates that MDGA1 and MDGA2 proteins are highly glycosylated, and that MDGA1 is tethered to the cell membrane by a GPI anchor. The MDGAs are differentially expressed by subpopulations of neurons in both the central and peripheral nervous systems, including neurons of the basilar pons, inferior olive, cerebellum, cerebral cortex, olfactory bulb, spinal cord, and dorsal root and trigeminal ganglia. Little or no MDGA expression is detected outside of the nervous system of developing rats. The similarity of MDGAs to other Ig-containing molecules and their temporal-spatial patterns of expression within restricted neuronal populations, for example migrating pontine neurons and D1 spinal interneurons, suggest a role for these novel proteins in regulating neuronal migration, as well as other aspects of neural development, including axon guidance.
Cell migration and axon guidance are important steps in the formation of neural circuits. Both st... more Cell migration and axon guidance are important steps in the formation of neural circuits. Both steps depend on the interactions between cell surface receptors and molecules on cells along the pathway. In addition to cellcell adhesion, these molecular interactions provide guidance information. The fine-tuning of cell-cell adhesion is as an important aspect of cell migration, axon guidance, and synapse formation. Here, we show that Endoglycan, a sialomucin, plays a role in axon guidance and cell migration in the central nervous system. In the absence of Endoglycan, commissural axons failed to cross the midline of the spinal cord. In the developing cerebellum, a lack of Endoglycan prevented migration of Purkinje cells and resulted in a stunted growth of the cerebellar lobes. Taken together, these results support the hypothesis that Endoglycan acts as a negative regulator of cell-cell adhesion in both commissural axon guidance and Purkinje cell migration.
Seminars in Neuroscience, Dec 1, 1996
Agrin, a basal lamina-associated proteoglycan, is a crucial nerve-derived organizer of postsynapt... more Agrin, a basal lamina-associated proteoglycan, is a crucial nerve-derived organizer of postsynaptic differentiation at the skeletal neuromuscular junction. Because integrins serve as cellular receptors for many basal lamina components, we asked whether agrin interacts with integrins. Agrin-induced aggregation of acetylcholine receptors on cultured myotubes was completely blocked by antibodies to the β1 integrin subunit and partially blocked by antibodies to the αv integrin subunit. Agrin-induced clustering was also inhibited by antisense oligonucleotides to αv and a peptide that blocks the αv binding site. Non-muscle cells that expressed αv and β1 integrin subunits adhered to immobilized agrin, and this adhesion was blocked by antiαv and anti-β1 antibodies. Integrin αv-negative cells that did not adhere to agrin were rendered adherent by introduction of αv. Together, these results implicate integrins, including αvβ1, as components or modulators of agrin's signal transduction pathway.
Springer eBooks, 1997
Upon arrival of a motor axon at the muscle fiber, signals released from its growth cone initiate ... more Upon arrival of a motor axon at the muscle fiber, signals released from its growth cone initiate the formation of a synapse. This process consists of two stages: arrest of axon growth at the target area and differentiation of pre-and postsynaptic cells at the site of nerve-muscle contact. Studies of regenerating neuromuscular junctions in vertebrates have revealed that important signals for the formation of this synapse are located in the synaptic basal lamina, and attempts to identify these signals have led to the isolation of agrin and other components. In this review, we discuss the evidence for the involvement of these molecules and their potential functional role in the formation and maintenance of the neuromuscular junction, with emphasis on agrin.
The Journal of Neuroscience, Dec 1, 1994
Depolarization of leech neurons growing on extracellular matrix extract (ECM) leads to cessation ... more Depolarization of leech neurons growing on extracellular matrix extract (ECM) leads to cessation of neurite outgrowth, rounding up of the peripheral regions of the growth cone, loss of filopodia, and neurite retraction. These responses depend on the influx of calcium (Neely, 1993). The aim of the present experiments was to analyze how the cytoskeleton becomes reorganized as growth cones change their morphology. lmmunocytochemistry revealed a loss of microfilaments in the tips of neurites growing on ECM after depolarization. Leech neurons cultured on a different substrate, the plant lectin concanavalin A (ConA), continue to grow during and after depolarization (Grumbacher-Reinert and Nicholls, 1992; Neely, 1993). As expected, we did not observe any change in the distribution of microfilaments after depolarization on ConA. Since there is evidence that this lack of response is due to a reduced calcium influx during depolarization of neurons on ConA (Ross et al., 1988), the effect of the calcium ionophore A23187 on the outgrowth of these cells was analyzed. In the absence of depolarization, this ionophore caused cessation of growth cone motility and a loss of microfilaments, while microtubules were not affected. Cytochalasin D, a microfilament-disrupting agent, induced changes in growth cone morphology and neurite retraction similar to those observed after depolarization and calcium influx. Application of phalloidin, a drug that stabilizes microfilaments, inhibited depolarization-induced retraction of neurites on ECM. By contrast, stabilization of microtubules with taxol did not prevent depolarization from inducing changes in growth cone morphology and neurite growth. These experiments show that changes in growth cone morphology and motility of leech neurons induced by depolarization and calcium influx are accompanied by a dramatic change in the organization of microfilaments, but not microtubules.
Journal of Cell Biology, Dec 15, 1995
Agrin is an extracellular matrix (ECM) protein with a calculated relative molecular mass of more ... more Agrin is an extracellular matrix (ECM) protein with a calculated relative molecular mass of more than 200 kD that induces the aggregation of acetylcholine receptors (AChRs) at the neuromuscular junction. This activity has been mapped to its COOH terminus.
Journal of Cell Biology, May 5, 1997
Journal of Cell Biology, Feb 15, 1995
Agrin is a basal lamina protein that induces aggregation of acetylcholine receptors (AChRs) and o... more Agrin is a basal lamina protein that induces aggregation of acetylcholine receptors (AChRs) and other molecules at the developing neuromuscular junction. Alternative splicing of chick agrin mRNA at two sites, A and B, gives rise to eight possible isoforms of which five are expressed in vivo. Motor neurons express high levels of isoforms with inserts at sites A and B, muscle cells synthesize isoforms that lack amino acids at the B-site. To obtain further insights into the mechanism of agrin-induced AChR aggregation, we have determined the ECs0 (effective concentration to induce half-maximal AChR clustering) of each agrin isoform and of truncation mutants. On chick myotubes, ECs0 of the COOH-terminal, 95-kD fragment of agrinA4a8 was ,'~35 pM, of agrinA4aZ9 ~110 pM and of agrinA4a,-5 nM. While some AChR clusters were observed with 64 nM of agrinA4aO, no activity was detected for agrinAoa0. Recombinant full-length chick agrin and a 100-kD fragment of ray agrin showed similar ECso values. A 45-kD, COOH-terminal fragment of agrinA4u retained high activity (ECso-130 pM) and a 21-kD fragment was still active, but required higher concentrations (ECs0-13 nM). Unlike the 45-kD fragment, the 21-kD fragment neither bound to heparin nor did heparin inhibit its capability to induce AChR aggregation. These data show quantitatively that agrinA4nS and agrinA4mg, expressed in motor neurons, are most active, while no activity is detected in agrinAoBo, the dominant isoform synthesized by muscle cells. Furthermore, our results show that a fragment comprising site Bs and the most COOHterminal G-like domain is sufficient for this activity, and that agrin domains required for binding to heparin and those for AChR aggregation are distinct from each other.
Neuron, Apr 1, 1996
Denzer et al., 1995). AChR-aggregating activity is con-Andrea Brancaccio, † Beat Schumacher,* fin... more Denzer et al., 1995). AChR-aggregating activity is con-Andrea Brancaccio, † Beat Schumacher,* fined to a 95 kDa C-terminal fragment (Nitkin et al., 1987; and Markus A. Ruegg* Tsim et al., 1992; Ferns et al., 1993), and further, *Department of Pharmacology N-terminal deletions in rat and chick agrin have revealed † Department of Biophysical Chemistry that a 45 kDa C-terminal fragment has similar activity Biozentrum (Hoch et al., 1994; Gesemann et al., 1995). Within this University of Basel fragment, two sites are modified by alternative mRNA CH-4056 Basel splicing (
BMC Neuroscience, Jul 2, 2007
Background: Development of neural networks requires that synapses are formed, eliminated and stab... more Background: Development of neural networks requires that synapses are formed, eliminated and stabilized. At the neuromuscular junction (NMJ), agrin/MuSK signaling, by triggering downstream pathways, causes clustering and phosphorylation of postsynaptic acetylcholine receptors (AChRs). Postnatally, AChR aggregates are stabilized by molecular pathways that are poorly characterized. Gain or loss of function of Src-family kinases (SFKs) disassembles AChR clusters at adult NMJs in vivo, whereas AChR aggregates disperse rapidly upon withdrawal of agrin from cultured src-/-;fyn-/myotubes. This suggests that a balance between protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) such as those of the Src-family may be essential in stabilizing clusters of AChRs. Results: We have analyzed the role of PTPs in maintenance of AChR aggregates, by adding and then withdrawing agrin from cultured myotubes in the presence of PTP or PTK inhibitors and quantitating remaining AChR clusters. In wild-type myotubes, blocking PTPs with pervanadate caused enhanced disassembly of AChR clusters after agrin withdrawal. When added at the time of agrin withdrawal, SFK inhibitors destabilized AChR aggregates but concomitant addition of pervanadate rescued cluster stability. Likewise in src-/-;fyn-/myotubes, in which agrin-induced AChR clusters form normally but rapidly disintegrate after agrin withdrawal, pervanadate addition stabilized AChR clusters. The PTP SHP-2, known to be enriched at the NMJ, associated and colocalized with MuSK, and agrin increased this interaction. Specific SHP-2 knockdown by RNA interference reduced the stability of AChR clusters in wild-type myotubes. Similarly, knockdown of SHP-2 in adult mouse soleus muscle by electroporation of RNA interference constructs caused disassembly of pretzel-shaped AChR-rich areas in vivo. Finally, we found that src-/-;fyn-/myotubes contained elevated levels of SHP-2 protein. Conclusion: Our data are the first to show that the fine balance between PTPs and SFKs is a key aspect in stabilization of postsynaptic AChR clusters. One phosphatase that acts in this equilibrium is SHP-2. Thus, PTPs such as SHP-2 stabilize AChR clusters under normal circumstances, but when these PTPs are not balanced by SFKs, they render clusters unstable.
The EMBO Journal, Jun 1, 1996
Agrin induces both phosphorylation and aggregation of nicotinic acetylcholine receptors (AChRs) w... more Agrin induces both phosphorylation and aggregation of nicotinic acetylcholine receptors (AChRs) when added to myotubes in culture, apparently by binding to a specific receptor on the myotube surface. One such agrin receptor is a-dystroglycan, although binding to a-dystroglycan appears not to mediate AChR aggregation. To determine whether agrin-induced AChR phosphorylation is mediated by a-dystroglycan or by a different agrin receptor, fragments of recombinant agrin that differ in affinity for a-dystroglycan were examined for their ability to induce AChR phosphorylation and aggregation in mouse C2 myotubes. The carboxy-terminal 95 kDa agrin fragment agrin-c95AQB0, which binds to a-dystroglycan with high affinity, failed to induce AChR phosphorylation and aggregation. In contrast, agrin-c95A4B8, which binds less strongly to a-dystroglycan, induced both phosphorylation and aggregation, as did a small 21 kDa fragment of agrin, agrin-c21B8, that completely lacks the binding domain for a-dystroglycan. We conclude that agrin-induced AChR phosphorylation and aggregation are triggered by an agrin receptor that is distinct from a-dystroglycan. Keywords: acetylcholine receptor/agrin/dystroglycan/neuromuscular junction/protein tyrosine phosphorylation.
Journal of Cell Science, 2014
Synaptic cell adhesion molecules (SynCAMs) are crucial for synapse formation and plasticity. Howe... more Synaptic cell adhesion molecules (SynCAMs) are crucial for synapse formation and plasticity. However, we have previously demonstrated that SynCAMs are also required during earlier stages of neural circuit formation because SynCAM1 and SynCAM2 (also known as CADM1 and CADM2, respectively) are important for the guidance of post-crossing commissural axons. In contrast to the exclusively homophilic cis-interactions reported by previous studies, our previous in vivo results suggested the existence of heterophilic cis-interactions between SynCAM1 and SynCAM2. Indeed, as we show here, the presence of homophilic and heterophilic cisinteractions modulates the interaction of SynCAMs with transbinding partners, as observed previously for other immunoglobulin superfamily cell adhesion molecules. These in vitro findings are in agreement with results from in vivo studies, which demonstrate a role for SynCAMs in the formation of sensory neural circuits in the chicken embryo. In the absence of SynCAMs, selective axon-axon interactions are perturbed resulting in aberrant pathfinding of sensory axons.
Journal of Biological Chemistry, 1998
Agrin is a basement membrane-associated proteoglycan that induces the formation of postsynaptic s... more Agrin is a basement membrane-associated proteoglycan that induces the formation of postsynaptic specializations at the neuromuscular junction. This activity is modulated by alternative splicing and is thought to be mediated by receptors expressed in muscle fibers. An isoform of agrin that does not induce postsynaptic specializations binds with high affinity to dystroglycan, a component of the dystrophin-glycoprotein complex. Transcripts encoding this agrin isoform are expressed in a variety of non-muscle tissues. Here, we analyzed the tissue distribution of agrin and dystroglycan on the protein level and determined their binding affinities. We found that agrin is most abundant in lung, kidney, and brain. Only a little agrin was detected in skeletal muscle, and no agrin was found in liver. Dystroglycan was highly expressed in all tissues examined except in liver. In a solid-phase radioligand binding assay, agrin bound to dystroglycan from lung, kidney, and skeletal muscle with a dissociation constant between 1.8 and 2.2 nM, while the affinity to brain-derived dystroglycan was 4.6 nM. In adult kidney and lung, agrin co-purified and coimmunoprecipitated with dystroglycan, and both molecules were co-localized in embryonic tissue. These data show that the agrin isoform expressed in non-muscle tissue is a high-affinity binding partner of dystroglycan and they suggest that this interaction, like that between laminin and dystroglycan, may be important for the mechanical integrity of the tissue. Agrin is a heparan sulfate proteoglycan that is required for the induction and regeneration of pre-and postsynaptic specializations at neuromuscular junctions (NMJ 1 ; Refs. 1 and 2). When applied to cultured chick myotubes, agrin leads to the formation of protein aggregates containing acetylcholine receptors (AChRs), acetylcholinesterase, and several other molecules that are also found at the neuromuscular junction in vivo (3). The aggregating activity of agrin is strongly influenced by alternative mRNA splicing at two sites, called A and B in chick
BMC Evolutionary Biology, 2012
Background: Opsins are key proteins in animal photoreception. Together with a light-sensitive gro... more Background: Opsins are key proteins in animal photoreception. Together with a light-sensitive group, the chromophore, they form visual pigments which initiate the visual transduction cascade when photoactivated. The spectral absorption properties of visual pigments are mainly determined by their opsins, and thus opsins are crucial for understanding the adaptations of animal eyes. Studies on the phylogeny and expression pattern of opsins have received considerable attention, but our knowledge about insect visual opsins is still limited. Up to now, researchers have focused on holometabolous insects, while general conclusions require sampling from a broader range of taxa. We have therefore investigated visual opsins in the ocelli and compound eyes of the two-spotted cricket Gryllus bimaculatus, a hemimetabolous insect. Results: Phylogenetic analyses place all identified cricket sequences within the three main visual opsin clades of insects. We assign three of these opsins to visual pigments found in the compound eyes with peak absorbances in the green (515 nm), blue (445 nm) and UV (332 nm) spectral range. Their expression pattern divides the retina into distinct regions: (1) the polarization-sensitive dorsal rim area with blue-and UV-opsin, (2) a newly-discovered ventral band of ommatidia with blue-and green-opsin and (3) the remainder of the compound eye with UV-and green-opsin. In addition, we provide evidence for two ocellar photopigments with peak absorbances in the green (511 nm) and UV (350 nm) spectral range, and with opsins that differ from those expressed in the compound eyes. Conclusions: Our data show that cricket eyes are spectrally more specialized than has previously been assumed, suggesting that similar adaptations in other insect species might have been overlooked. The arrangement of spectral receptor types within some ommatidia of the cricket compound eyes differs from the generally accepted pattern found in holometabolous insect taxa and awaits a functional explanation. From the opsin phylogeny, we conclude that gene duplications, which permitted differential opsin expression in insect ocelli and compound eyes, occurred independently in several insect lineages and are recent compared to the origin of the eyes themselves.
In the central nervous system of vertebrates, glutamate serves as the primary excitatory neurotra... more In the central nervous system of vertebrates, glutamate serves as the primary excitatory neurotransmitter. However, in the retina, glutamate released from photoreceptors causes hyperpolarization in postsynaptic ON-bipolar cells through a glutamate-gated chloride current, which seems paradoxical. Our research reveals that this current is modulated by two excitatory glutamate transporters, EAAT5b and EAAT7. These transporters are located at the dendritic tips of ON-bipolar cells and interact with all four types of cone photoreceptors. The absence of these transporters leads to a decrease in ON-bipolar cell responses, with eaat5b mutants being more severely affected than eaat5b/eaat7 double mutants, which also exhibit altered response kinetics. Biophysical investigations establish that EAAT7 is an active glutamate transporter with a predominant anion conductance. Our study is the first to demonstrate the direct involvement of postsynaptic glutamate transporters in inhibitory direct syn...
SummaryPrimary cilia are key sensory organelles whose dysfunction leads to ciliopathy disorders s... more SummaryPrimary cilia are key sensory organelles whose dysfunction leads to ciliopathy disorders such as Bardet-Biedl syndrome (BBS). Retinal degeneration is common in ciliopathies, since the outer segments (OSs) of photoreceptors are highly specialized primary cilia. BBS1, encoded by the most commonly mutated BBS-associated gene, is part of the BBSome protein complex. Using a new bbs1 zebrafish mutant, we show that retinal development and photoreceptor differentiation are unaffected by Bbs1-loss, supported by an initially unaffected transcriptome. Quantitative proteomics and lipidomics on isolated OSs show that Bbs1 is required for BBSome-entry into OSs and that Bbs1-loss leads to accumulation of membrane-associated proteins in OSs, with enrichment in proteins involved in lipid homeostasis. Disruption of the tightly regulated OS lipid composition with increased OS cholesterol content are paralleled by early functional visual deficits, which precede progressive OS morphological anoma...
Investigative Ophthalmology & Visual Science, 2014
Investigative Ophthalmology & Visual Science, 2010
Investigative Ophthalmology & Visual Science, 2009
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Papers by Matthias Gesemann