Columbia
University
Biological Sciences
1003b Fairchild Center, M.C. 2442
New York, N.Y. 10027
212-854-5125
E-mail erm3@columbia.edu
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Our studies focus on the cellular and molecular mechanisms underlying the specification of neuronal identity, growth cone motility and navigation, target selection and the generation of neuronal arbors. We work with identified neurons in the medicinal leech, Hirudo medicinalis, a system that has several advantages for our studies. First, we can study a particular neuron at all stages of development, in the animal; second, we can visualize many cells in the intact animal as they differentiate, using time-lapse 2-photon confocal imaging, and operate on them with a laser microbeam to ask very specific questions; and third, we can inject macromolecules into embryonic or adult neurons, which means that we can transform a single cell in a wild-type environment.
In current cellular studies, we are examining the formation of peripheral arbors by sensory and motor projections in the animal's bodywall and in specific target tissues, like the heart tubes. Time-lapse observations in situ show that arbors are highly dynamic, with higher-order branches undergoing repeated cycles of extension and retraction. We have also identified several interactions (e.g., between homologous neurons, between pioneers and their followers, between axons and non-neuronal substrates, between different branches of the same neuron, between neurons and their targets) that play roles in defining the size and shape of the arbor. One experiment underway explores how a cell recognizes itself by examining what happens after a branch has been severed by laser photoablation - the result is that the cell stops recognizing the distal stump as self, suggesting that surface markers are not responsible for self recognition. To get some incling of how back-branching might be induced by interactions with substrates or targets, in another set of experiments we are beginning to map the disposition and dynamics of cytoskeletal proteins at branch points forming behind growth cones.
Among current molecular studies, we are continuing the characterization of a family of transcription factors that are thought to be responsible for the specification of neuronal phenotype. These are genes of the Hox/HOM homeobox family, which we were the first to clone and characterize in the leech (e.g., Lox1, Lox2, Lox3, Lox4, Lox6, Lox 15). They are expressed in overlapping sets in the leech nervous system. We have identified several neurons that express them, and have found in some cases that changes or differences in expression correlate with phenotypic differences among segmental homologues. These differences include changes in arborization patterns and peripheral targets, tying these molecular studies to the cellular studies summarized above. On-going efforts to affect expression will test whether these correlations signify causal relationships. An initial result of expressing Lox1 ectopically by injecting its mRNA in adult neurons is a reproducible change in the electrical properties of the injected cells.
In a complementary set of molecular studies, we have begun to examine the
functions of membrane-bound and secreted recognition/adhesion factors that
are thought to be involved in the cell interactions we have documented to
occur during arbor formation and target selection. We have recently
cloned the leech homologues, HmLAR1 and HmLAR2, of the LAR family of
receptor phosphatases and have determined that they are expressed by
identified neurons (in processes and growth cones) as well as some muscle
and other types of cells. Blocking function by injecting into embryos
antibodies to the extracellular domain or recombinantly expressed
extracellular domains, or using RNAi in tissues or individual cells to knock down
expression of these receptors, shows that HmLAR1, which is expressed by the heart
tubes, is necessary for the innervation of the heart, and that HmLAR2 is
involved in the regulation of axonal pathfinding growth cone stability and process
outgrowth. In addition, we have characterized a leech netrin, which is also expressed by specific
central neurons as well as ventral (but not dorsal) longitudinal muscles.
Initial results of injecting leech netrin antibodies into live embryos
suggest that afferent projections may use a netrin gradient to grow
towards the central nervous. We are presently beginning to examine the
formation of peripheral neuronal arbors in the presence of these blocking
antibodies.
Research in this laboratory is supported by grants from the National Science Foundation and the National Institutes of Health.
M.W. Baker and E.R. Macagno. (2000) RNAi of the Receptor Tyrosine Phosphatase HmLAR2 in a Single Cell of an Intact Leech Embryo Leads to Growth Cone Collapse. Current Biology, in the Press.
Possible Role of the Receptor Protein Tyrosine Phosphatase HmLAR2 in Interbranch Repulsion in a Leech Embryonic Cell. (2000) M.W. Baker, S.J. Rauth and E.R. Macagno. J. Neurobiol., in the Press.
The Role of a LAR-like Receptor Tyrosine Phosphatase in Growth Cone Collapse and Mutual-Avoidance by Sibling Processes. (2000) M.W. Baker and E.R. Macagno. J. Neurobiol. 44:194-203.
M.W. Baker and E.R.. Macagno. (2000) Neuronal Growth and Target Recognition: Lessons from the Leech. Can. J. Zool., in the Press.
Michael W. Baker, Timothy R. Gershon and E.R. Macagno. Antibodies to the Ectodomain of the Receptor Protein Tyrosine Phosphatase HmLAR1 Block Innervation of the Heart in the Leech. (2000) In preparation.
WenBiao Gan, Victoria Y. Wong, Aloysius Phillips, Charles Ma, Timothy Gershon and E.R. Macagno. (1999) Cellular Expression of a Leech Netrin Suggests Roles in the Formation of Longitudinal Nerve Tracts and in the Regional Innervation of Peripheral Targets. J. Neurobiol. 40:103-115.
Timothy R. Gershon, Michael W. Baker, Michael N. Nitabach and E.R. Macagno.The Receptor Protein Tyrosine Phosphatase HmLAR2 is Concentrated in Growth Cones and Is Involved in Process Outgrowth (1998). Development, 125:1183-1190. Abstract
Timothy R. Gershon, Michael W. Baker, Michael N. Nitabach, Peter Wu and E.R. Macagno. Two Receptor Tyrosine Phosphatases of the LAR Family Are Expressed in the Developing Leech by Specific Central Neurons as well as Select Peripheral Neurons, Muscles and Other Cells. (1998) J Neurosci. 18:2991-3002. Abstract
Huajun Wang and E.R. Macagno. A Severed Branch Ceases to Be Recognized as Self by a Neuron (1998). J. Neurobiol. 35:53-64. Abstract
Thomas S. Becker, Gerald Bothe, Alexis R. Harley and E.R. Macagno. (1998) Cell Proliferation in a Peripheral Target is Required for the Induction of Central neurogenesis in the Leech. J. Neurobiol., 34:195:303. Abstract
Victoria Y. Wong and E.R. Macagno. Lox6, a Leech Dfd ortholog, Is Expressed in the Central Nervous System and in Peripheral Sensory Structures (1998). Devel. Genes Evol, 208:51-55. Abstract
Huajun Wang and E.R. Macagno. (1997). The Establishment of Peripheral Sensory Arbors in the Leech. In vivo Time-lapse Studies Reveal a Highly Dynamic Process. J. Neurosci. 17:2408-2419.Abstract
Gabriel O. Aisemberg, Timothy R. Gershon and E.R. Macagno. (1997) New Electrical Properties of Neurons Induced by a Homeoprotein. J. Neurobiol. 32: 11-17.Abstract
WenBiao Gan and E.R. Macagno. (1997) Competition among the Axonal Projections of an Identified Neuron Contributes to the Retraction of some of those Projections. J. Neurosci. 17:4293-4301.Abstract
T.S. Becker, G. Bothe, A.J. Berliner and E.R. Macagno. (1996). Identified Central Neurons Convey a Mitogenic Signal from a Peripheral Target to the CNS. Development 122:2331-2337.Abstract
Nitabach, M. and E.R. Macagno(1995) Cell- and tissue-specific expression of protein kinase mRNAs in the embryonic leech, Hirudomedicinalis. Cell Tissue Res. 280:479-489. Abstract
Gan, W.B. and E.R. Macagno (1995) Interactions between segmental homologous and between isoneuronal branches guide the formation of sensory terminal fields. J. Neurosci. 15:3243-3253.Abstract
Wong, V.Y., Aisemberg, G.O. and E.R. Macagno (1995) The leech homeobox gene Lox4 may determine the segmental differentiation of identified neurons. J. Neurosci. 15:5551-5559. Abstract
Gan, W.B. and E.R. Macagno (1995) Developing neurons use a pioneer's peripheral arbor to establish their terminal fields. J. Neurosci. 15:3254-3262.Abstract
Becker, T., Berliner, A., Nitabach, M., Gan, W.B. and E.R. Macagno (1995) Target-induced neurogenesis in the leech CNS involves efferent projections to the target. Development 121:359- 369.Abstract
L.R. Wolszon, M.B. Passani and E.R. Macagno. (1995). Interactions during a Critical Period Inhibit Bilateral Projections in Embryonic Neurons. J. Neurosci. 15:1506-1515.Abstract
G.O. Aisemberg, V.Y. Wong and E.R. Macagno. (1995). Genesis of Segmental Identity in the Leech Nervous System. In: The Nervous Systems of Invertebrates: An Evolutionary and Comparative Approach, O. Breidbach and W. Kutsch, eds., Birkhauser-Verlag, Berlin, pp.77-87.Abstract
J. Wysocka-Diller, G. Aisemberg and E.R. Macagno. (1995). The Lox3 Complex: a Set of Nearly Identical Genes Expressed in Antero-Posterior Stripes during Morphogenesis of the Leech Gut. Develop. Biol. 171:439-447 Abstract
Wolszon, L.R., Gao, W.-Q., Passani, M.B. and E.R. Macagno (1994) Growth cone "collapse" in vivo: Are inhibitory interactions mediated by gap junctions? J. Neurosci. 14:999-1010.Abstract
Wolszon, L.R., Rehder, V., Kater, S.B., and E.R. Macagno (1994) Calcium wave fronts that cross gap junctions may signal neuronal death during embryogenesis. Neurosci. 14:3437-3448.Abstract
G.O. Aisemberg and E.R. Macagno. (1994). Lox1: An Antennapedia-class Homeobox Gene Expressed During Leech Gangliogenesis in Both Transient and Stable Central Neurons. Develop. Biol. 161:455-465Abstract
J. Ngai, A. Chess, M. M. Dowling, N. Necles, E. R. Macagno and R. Axel. (1993). Coding of Olfactory Information: Topography of Odorant Receptor Expression in the Catfish Olfactory Epithelium. Cell 72:667-680Abstract
G.O. Aisemberg, J. Wysocka-Diller, V.Y. Wong and E.R. Macagno. (1993). Antennapedia-class Homeobox Genes Define Diverse Neuronal Sets in the Embryonic CNS of the Leech. J. Neurobiol. 24:1423-1432 Abstract
T. Becker and E.R. Macagno. (1992). Control of Central Neurogenesis in the Leech. In: Determinants of Cell Fate, Eds: M. Shankland and E.R. Macagno, Academic Press, New York, pp. 79-95
T. Becker and E.R. Macagno. (1992). CNS Control of a Critical Period for Peripheral Induction of Central Neurons in the Leech. Development 116:427-434 Abstract
J.M. Camhi and E.R. Macagno. (1991). Using Fluorescence Photoablation to Study the Regeneration of Singly Cut Leech Axons. J. Neurobiol. 22:116-129 Abstract
R.R. Stewart, W.-Q. Gao and E.R. Macagno. (1991). Segmental Differentiation in the Leech Nervous System: Proposed Homologs of the Heart Accessory Neurons. J. Comp. Neurol. 313:431-440Abstract
L.R. Wolszon and E.R. Macagno. (1991). Growth Cone Interactions and the Patterns of Peripheral Innervation in the Leech. In: The Nerve Growth Cone, Eds: P.C. Letourneau, S.B. Kater and E.R. Macagno, Raven Press, New York, pp. 305-322
M.B. Passani, A. Peinado, H. Engelman, C.A. Baptista and E.R. Macagno. (1991). Normally Unused Positional Cues Guide Ectopic Afferents in the Leech Central Nervous System. J. Neurosci. 11:3868-3876Abstract
T.R. Consi, M.B. Passani and E.R. Macagno. (1990). Eye Movements in Daphnia magna. Regions of the Eye are Specialized for Different Behaviors. J. Comp. Physiol. A166:411-420Abstract
M. Levine and E.R. Macagno. (1990). Segmentation and Segmental Differentiation in the Development of the Central Nervous Systems of Leeches and Flies. Ann. Rev. Neurosci. 13:195-225
E.R. Macagno, W.-Q. Gao, C.A. Baptista and M.B. Passani. (1990). Competition or Inhibition? Developmental Strategies in the Establishment of Peripheral Projections by Leech Neurons. J Neurobiol 1990 Jan;21(1):107-119Abstract
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