Margret I. Moré (Ph.D.)

                                MDC
                                Robert-Rössle-Str. 10
                                D - 13092 Berlin-Buch
                                Germany

                                Phone:  +49-30-9406-3709
                                Fax:    +49-30-9406-3730
                                mmore@mdc-berlin.de

                                1997 - 2004 member of Fritz G. Rathjen's group
                                since Oct 2004 teacher at BBB Management GmbH, Gläsernes Labor


                                                                        NrCAM
The transmembrane glycoprotein NrCAM is a member of the L1 subgroup of Ig-like cell adhesion proteins. This subgroup is composed of NrCAM, neurofascin, CHL1 and L1 itself in vertebrates and neuroglian and tractin in invertebrates. Like L1, NrCAM contains six Ig-like domains and five FNIII-like repeats, a hydrophobic stretch and a highly conserved cytoplasmic segment (see first figure). A crucial role of the L1 subgroup of proteins in neural development is exemplified by a broad spectrum of neuroanatomical and neurological disorders caused by the knock-out of the murine L1 gene and by mutations in the human L1 gene which affect the binding activity and trafficking of L1. As also shown for other L1 subgroup members, NrCAM reveals a complex homo- and heterophilic binding pattern and is implicated in cell-cell contact processes. In in vitro bioassays it can promote axonal growth by binding to neurofascin, F11 or RPTP, and can mediate interactions between neurons and glial cells via axonin-1. In ovo antibody perturbation experiments indicate that NrCAM is important for commissural axons of the chicken spinal cord to grow across the midline through the floor plate and for proprioceptive axon collaterals to extend ventrally within the spinal cord. NrCAM has also been found to be expressed specifically at the node of Ranvier in rat where it interacts with the cytoskeletal adaptor protein ankyrin-G. Binding to ankyrin appears to be a common feature of L1 subfamily members and requires a highly conserved sequence within their cytoplasmic tails. This interaction appears to be inhibited by tyrosine phosphorylation as demonstrated for neurofascin whereas clustering of the L1 subfamily member neuroglian at adhesion sites activates ankyrin binding followed by a redistribution of spectrin.

In my work we have been focussing on the function of the NrCAM protein in vivo. For this we generated NrCAM knock-out mice by gene targeting. The mice are viable and fertile, but smaller than heterozygous or wild-type littermates, and they show a slight motor defect. Also, females have a tendency to abandon their pups. Although NrCAM -/- neurons, unlike wild-type are unable to grow on neurofascin and F11 in cell culture, NrCAM -/- mice have no significant abnormalities on a histological level in any of their neural tissues. Significant pathfinding errors of commissural axons at the midline of the spinal cord or of proprioceptive axon collaterals are not detected. Interestingly, we found that the absence of NrCAM causes the formation of mature cataracts in the mouse.  Cataracts are the most common cause of visual impairment. In NrCAM deficient mice they are generated by a disorganization of lens fibres, followed by cellular disintegration and accumulation of cellular debris (see second figure: section through a 2 month-old mutant lens, anterior is up). The disorganization of fibre cells becomes histologically distinct during late embryonic development.  It includes abnormalities of the cytoskeleton and of connexin50 containing gap junctions. Furthermore, analysis of lenses of ankyrin-B mutant mice also reveals a disorganization of lens fibres at postnatal day one indistinguishable from that generated by the absence of NrCAM. This indicates that both NrCAM and ankyrin-B are required to maintain contact between lens fibre cells. Also, our studies provide genetic evidence of an interaction between NrCAM and ankyrin-B.

This work has been published in the Journal of Cell Biology.

                                                                      CALEB

CALEB is a transmembrane glycoprotein containing an EGF-like domain resembling that of neuregulins, as well as an acidic box. Extracellularly, CALEB can interact with the extracellular matrix proteins tenascin-C and tenascin-R. It is strongly expressed in the developing nervous system.
Interestingly, neuronal depolarization facilitates the conversion of CALEB protein to a truncated transmembrane form with an exposed EGF domain.

In order to examine the role of CALEB in synapse development, we generated CALEB deficient mice. At first glance CALEB deficient mice are viable and fertile and show no gross abnormalities. We investigated the synaptic features in slices of the colliculus superior from CALEB-deficient mice. In the absence of CALEB, the number of synapses and their morphological characteristics remained unchanged. However, in CALEB-deficient mice, synapses displayed higher paired-pulse ratios, less depression during prolonged repetitive activation, a lower rate of spontaneous postsynaptic currents, and a lower release probability at early but not mature postnatal stages. Our findings indicate that CALEB provides a molecular basis for maintaining normal release probability at early developmental stages

                                                                      N-cadherin

N-Cadherin (N-cad) is one of the major Ca(2+)-dependent cell adhesion proteins in the developing nervous system and plays an important role in establishing and maintaining cell-cell contact. Like most other classical cadherins, N-cad forms cis-dimers and its extracellular domain engages in homophilic binding in trans. The cytoplasmic domain of N-cad interacts with the kinase p120 and b-catenin which in turn is linked to the actin cytoskeleton via a-catenin.
During early vertebrate development, N-cad is ubiquitously expressed. Zebrafish N-cad is strongly expressed in all retinal precursor cells (24 hpf) and expression continues beyond day 8 within all retinal layers, with slightly reduced levels once lamination is complete, and with highest expression levels within the plexiform layers. Also N-cad is strongly expressed in the lens primordium (24 hpf), as well as the lens epithelium and lens fibres of the developing lens (40 hpf), with a downregulation in the lens fibers at later stages.

Together with my co-workers, I have analyzed the eye development in the zebrafish N-cad loss-of-function mutant parachute (pacpaR2.10), provided by Laure Bally-Cuif, GSF, Munich. The zebrafish visual system is fully developed by the time pacpaR2.10 mutants show lethality at day 5. Already at 24 hr postfertilization (hpf), mutant retinal cells are more disorganized and more rounded than in wild-type. At later stages, mutant retinae display a severe lamination defect with rosette formation (see figure; mostly islands of plexiform layer tissue surrounded by inner nuclear layer or photoreceptor cells), even though all major classes of cell types appear to be present as determined by histology. Of interest, electron microscopy reveals that the islands of plexiform layer tissue contain a normal amount of synapses with normal morphology. Although mutant photoreceptor cells are sometimes deformed, all typical structural components are present, including the membranous discs for rhodopsin storage. The lens fibers of the pac(paR2.10) mutants develop completely normally, but in some cases, lens epithelial cells round up and become multilayered. We conclude that cell adhesion mediated by N-cad is of major importance for retinal lamination and involved in maintenance of the lens epithelial sheet, but is not essential for the formation of photoreceptor ultrastructure or for synaptogenesis.


 My work was helped along by technical help of Frank-P. Kirsch and Yvone Klosowski and especially by helpful scientific input from Fritz G. Rathjen.

Publications:

R. Jüttner, M. I. Moré, D. Das, A. Babich, J. Meier, M. Henning, B. Erdmann, E.-C. Müller, A. Otto, R. Grantyn, and F. G. Rathjen (2005). Impaired synapse function during postnatal development in the absence of CALEB, an EGF-like protein processed by neuronal activity (abstract). Neuron 46, 233-245.  

B. Erdmann, F.-P. Kirsch, F. G. Rathjen, M. I. More. 2003. N-Cadherin is essential for retinal lamination in the zebrafish (abstract). Dev. Dyn. 2003 226, 570-577.

H. Schmidt, M. Werner, P. A. Heppenstall, M. Henning,  M. I. More, S. Kühbandner, G. R. Lewin, F. Hofmann, R.Feil  and F. G. Rathjen.  2002. cGMP-mediated signalling via cGKI-alpha is required for the guidance and connectivity of sensory axons (abstract). The Journal of Cell Biology 159, 489-498.

M. I. Moré, F.-P. Kirsch, F. G. Rathjen.  2001. Targeted ablation of NrCAM or ankyrin-B results in disorganized lens fibres leading to cataract formation. (abstract). The Journal of Cell Biology, 154, 187-196

 S. Paterson, M. I. Moré, G. Pillay, C. Cellini, R. Woodgate, G. C. Walker, V. N. Iyer, and S. C. Winans.  1999.  Genetic analysis of the mobilization and leading regions of the IncN plasmids pKM101 and pCU1. J. Bacteriol. 181, 2572-2583.

J. Zhu, J. W. Beaber, M. I. More, C. Fuqua, A. Eberhard, S. C. Winans (1998).  Analogs of the autoinducer 3-oxooctanoyl-homoserine lactone strongly inhibit activity of the TraR protein of Agrobacterium tumefaciens.  J. Bacteriol. 180,  5398-5405.

S.C. Winans and M. I. Moré  (1996).  Response to: The inner workings of a quorum sensing signal generator,  S. Swift, G. S. A. B. Stewart and P. Williams.  TIM 4, 465-466.

M. I.  Moré, L. D. Finger, J. L. Stryker, A. Eberhard, C. Fuqua, and S. C. Winans (1996). Enzymatic synthesis of a quorum-sensing autoinducer through the use of defined substrates.  Science 272, 1655-1658.

M. I.  Moré, R. F. Pohlman, and S. C. Winans (1996). Genes encoding the pKM101 mating pore are negatively regulated by the plasmid-encoded KorA and KorB proteins.  J. Bacteriol. 178, 4392-4399.

M. C. Silva, M. I.  Moré, and C. A. Batt (1995). Development of a molecular detection method for naphthalene degrading pseudomonads. FEMS Microbiol. Ecol. 18, 225-235.

M. I. Moré, J. B. Herrick, M. C. Silva, W. C. Ghiorse, and E. L. Madsen (1994). Quantitative cell lysis of indigenous microorganisms and rapid extraction of microbial DNA from sediment. Appl. Env. Microbiol. 60, 1572-1580.

R. F. Pohlman, F. Liu, M. I. Moré, and S. C. Winans (1993). Genetic and biochemical analysis of an endonuclease encoded by the IncN plasmid pKM101. Nucl. Acid. Res. 21, 4867-4872.

Theses

M. I. Moré (1997) Regulation of conjugal transfer: Quorum dependent positive regulation of conjugation in Agrobacterium tumefaciens und negative regulation of conjugal operons by KorA und KorB of the IncN plasmid pKM101 in E. coli. Ph. D. Thesis, Cornell University, Section of Microbiology.

L. D. Finger, Margret I.Moré, A. Eberhard, S. C. Winans (1996) A novel synthetic method for the preparation of 3-oxoacylcoenzyme A and acyl carrier protein derivatives. B. S. Honors Thesis, Ithaca College, Department of Chemistry.

Book Chapters

S. C. Winans, J. Zhu, and M. I. Moré  (1999).  Cell density-dependent gene expression by Agrobacterium tumefaciens during colonization of crown gall tumors. in Cell-Cell Signaling in Bacteria.  G. M. Dunny,  and S. C. Winans (Eds).  ASM Press, Washington, D. C.

S.C.Winans, L. Wang, P. Dwen, C. Fuqua, M. I. Moré, J. Alt-Mörbe, J. Stryker, and M. Burbea  (1996).  Transcriptional regulation of conjugal transfer genes of octopine-type Ti plasmids. pp. 59-74.  in Crown Gall: Advances in Understanding Interkingdom Gene Transfer.  W. Ream and S.B. Gelvin (Eds). American Phytopathology Society, St Paul.


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     MDC               Fritz G. Rathjen's group                                      Gläsernes Labor
Max-Delbrueck-Center
for Molecular Medicine