Rosalind A. Segal, MD/PhD
Associate Professor of Neurology
Harvard Medical School/Beth Israel
Deaconess Medical Center
MRRC Project(s)
R01 NS37757-03
Cell-Cell Interactions in Cerebellar Development
R01 NS35148-05
Retrograde Signal Transduction by Neurotrophins
Our research is directed at the mechanisms by which extracellular stimuli regulate the developing nervous system. We have focused on the neurotrophins, their functions and mechanisms of action. There are two central areas of research. The first emphasizes the functions of neurotrophins and other extracellular factors in regulating cerebellar development. The second is focused on the mechanisms by which target-derived neurotrophic factors propagate a signal through a long axon.
Research Description
Highlights of Major Accomplishments
Major Results
The neurotrophin, brain-derived neurotrophic factor (BDNF), promotes survival and axonal elongation of developing granule cells. In contrast, the highly related factor, neurotrophin-3 (NT-3), has distinct effects on development. To examine the roles of these factors in vivo, we have made use of mice with induced mutations in the genes encoding the neurotrophins or their receptors.
Mice with a targeted gene deletion of brain-derived neurotrophic factor (BDNF) exhibit an ataxic gait. Consistent with this behavioral evidence of cerebellar dysfunction, there is increased death of developing granule cells, stunting of Purkinje cell dendrites and defects in the rostral-caudal foliation pattern. These abnormalities are accompanied by decreased Trk activation in granule and Purkinje cells of mutant animals, indicating that both cell types are direct targets for BDNF. These data suggest that BDNF acts as an anterograde and an autocrine/paracrine factor to regulate both survival and morphologic differentiation of developing CNS neurons, and thereby affects neural patterning. (This work was done in collaboration with Dr. Scott Pomeroy of this MRRC.)
Recently, we have found that the migration of granule cells from the external granule layer (EGL) to the internal granule layer (IGL) is impaired in BDNF -/- mice. Furthermore, BDNF directly regulates the initiation of granule cell migration. In mutant animals, failure of granule cell migration results in granule cell hyperproliferation. These data suggest that one mechanism by which neuronal precursor proliferation is regulated is the migration of precursors away from proliferative zones.
Understanding the mechanisms of action of neurotrophins in normal neurons requires a consideration of spatial constraints. For a target-derived neurotrophin to regulate the survival of a presynaptic cell, a signal must be propagated from the nerve terminal along the axon to the nucleus. In collaboration with Dr. Charles Stiles of this MRRC, we are using the sciatic nerve of adult rat and compartmented chamber cultures of embryonic neurons as systems in which to identify the molecule(s) that carry the signal(s) along the axon, and the mechanism for signal propagation. Using phosphorylation state-specific antibodies to neurotrophin receptors (Trks) we demonstrated that phosphorylated Trks, distributed all along the length of sciatic nerve axons, are catalytically active and are associated with signal generating proteins. Neurotrophins applied at the nerve terminal activate distant axonal Trk receptors, and this activation propagates rapidly through the axon toward the nerve cell body. Thus, activated Trk receptors function as rapid retrograde signal carriers to elicit nuclear responses to target-derived neurotrophins. Once the activated receptors reach the cell body, they elicit nuclear responses- including phosphorylation of the transcription factor CREB and subsequent induction of the immediate early genes c-fos and c-jun.
We used GFP-tagged Trk receptors to determine the mechanism by which the retrograde phospho-Trk signal is propagated. Our data indicate that signal propagation represents retrograde vesicular transport of activated Trk-ligand complexes. Together these data support a model of retrograde signaling whereby rapid vesicular transport of ligand-receptor complex from the neurites to the cell bodies mediates nuclear responses. Recent studies have focused on identifying the molecular requirements for this internalization and transport. We have shown that Trk internalization requires the GTP-ase dynamin. We are now using the Trk-GFP transport assay to define the characteristics of the Trk receptor that allow internalization and transport and to identify differences in signaling pathways activated in response to plasma membrane embedded receptors versus those located within vesicles.
Publications
Segal RA, Bhattacharyya A, Rua L, Alberta JA, Stephens RM, Kaplan DR, Stiles CD. Differential utilization of Trk autophosphorylation sites in vivo. J Biol Chem 1996; 271:20175-20181.
Segal RA, Greenberg ME. Intracellular signaling pathways activated by neurotrophic factors. Annu Rev Neurosci 1996; 19:463-489.
Segal RA, Rua L, Schwartz P. Neurotrophins and programmed cell death during cerebellar development. Advances in Neurology 1997; 72: Chapter 8.
Pomeroy SL, Sutton ME, Goumnerova LC, Segal RA. Neurotrophins in cerebellar granule cell development and medulloblastoma. J Neuro-Oncol 1997; 35:347-352.
Nachmanoff D, Segal RA, Brown RB, De Girolami U, Dawson DM. Hereditary ataxia with sensory neuronopathy: Biemond's ataxia. Neurology 1997; 48:273-275.
Dudek H, Datta SR, Franke TF, Birnbaum MJ, Yao R, Cooper GM, Segal RA, Kaplan DR, Greenberg ME. Regulation of neuronal survival by the ser/thr protein kinase Akt. Science 1997; 275: 661-665.
Cabelli RJ, Shelton D, Segal RA, Shatz CJ. Blockade of endogenous ligands of trkB inhibits formation of ocular dominance columns. Neuron 1997; 19:63-76.
Schwartz PM, Borghesani, Levy RL, Pomeroy SL, Segal RA. Abnormal cerebellar development and foliation in BDNF -/- mice reveals a role for neurotrophins in CNS patterning. Neuron 1997; 19:269-281.
Bhattacharyya A, Watson FL, Bradlee TA, Pomeroy SL, Stiles CD, Segal RA. Trk receptors function as retrograde signal carriers in the adult nervous system. J Neurosci 1997; 17:7007-7016.
Schwartz PM, Borghesani PR, Levy RL, Segal RA. Cerebellar pathology in BDNF -/- mice: The classic view of neurotrophins is changing. Molec Psychiatr 1998; 3:116-118.
Ma Q, Jones D, Borghesani PR, Segal RA, Nagasawa T, Kishimoto T, Bronson, RT, Springer TA. Impaired B-lymphopoiesis, myelopoiesis and derailed cerebellar neuron migration in CXCR4 and SDF-1 deficient mice. Proc Natl Acad Sci USA 1998; 95:9448-53.
Kim J, Sutton ME, Lu DJ, Cho TA, Goumnerova LC, Goritchenko L, Lam KK, Allen JC, Wu J, Tarbell NJ, Billett AL, Segal RA, Pomeroy SL. Activation of neurotrophin-3 receptor TrkC induces apoptosis in medulloblastomas. Cancer Res 1999; 59:711-719.
Watson FL, Porcionatto MA, Bhattacharyya A, Stiles CD, Segal RA. TrkA glycosylation regulates receptor localization and activity. J Neurobiol 1999; 39:323-336.
Watson FL, Heersson HM, Moheban DB, Lin MZ, Sauvageot CM, Pomeroy SL, Bhattacharyya A, Segal RA. Rapid nuclear responses to target derived neurotrophins require retrograde transport of ligand-receptor complex. J Neurosci 1999; 19:7889-7900.
Zhang YZ, Moheban DB, Conway BR, Bhattacharyya A, Segal RA. NGF-induced differentiation and survival are controlled by receptors signaling from distinct intracellular locations. Submitted.
Borghesani PR, Alt
FW, Bottaro A, Davidson L, Aksoy S, Rathbun GA, Roberts TM, Swat W, Segal
RA, Gu Y. Abnormal development of Purkinje cells and lymphocytes in Atm
mutant mice. PNAS USA 2000;97(7):3336-41.
Wang KC, Kim JA, Sivasankaran R, Segal R, He Z. p75 interacts with the
Nogo receptor as a co-receptor for Nogo, MAG and OMgp. Nature 2002;420(74-78).
Segal RA, Martonen TB, Kim CS, Shearer M. Computer simulations of particle
deposition in the lungs of chronic obstructive pulmonary disease patients.
Inhal Toxicol 2002;14(7):705-20. 4
Kim JY, Koralnik IJ, LeFave M, Segal RA, Pfister LA, Pomeroy SL. Medulloblastomas
and primitive neuroectodermal tumors rarely contain polyomavirus DNA sequences.
Neuro-oncol 2002;4(3):165-70.
Ginty DD, Segal RA. Retrograde neurotrophin signaling: Trk-ing along the
axon. Curr Opin Neurobiol 2002;12(3):268-74.
Rubin JB, Choi Y, Segal RA. Cerebellar proteoglycans regulate sonic hedgehog
responses during development. Development 2002;129(9):2223-32.
Borghesani PR, Peyrin JM, Klein R, Rubin J, Carter AR, Schwartz PM, Luster
A, Corfas G, Segal RA. BDNF stimulates migration of cerebellar granule
cells. Development 2002;129(6):1435-42.
Heerssen HM, Segal RA. Location, location, location: a spatial view of
neurotrophin signal transduction. TINS 2002;25(3):160-5.
Carter AR, Chen C, Schwartz PM, Segal RA. Brain-derived neurotrophic factor
modulates cerebellar plasticity and synaptic ultrastructure. J Neurosci
2002;22(4):1316-27.
Bhattacharyya A, Watson FL, Pomeroy SL, Zhang YZ, Stiles CD, Segal RA.
High-resolution imaging demonstrates dynein-based vesicular transport
of activated Trk receptors. J Neurobiol 2002;51(4):302-12.
Carter AR, Berry EM, Segal RA. Regional expression of p75NTR contributes
to neurotrophin regulation of cerebellar patterning. Mol Cell Neurosci
2003;22(1):1-13.
Segal RA. Selectivity in neurotrophin signaling: theme and variations.
Annu Rev Neurosci 2003;26:299-330.
Rubin JB, Segal RA. Growth, survival and migration: the Trk to cancer.
Cancer Treat Res 2003;115:1-18.
Rubin JB, Kung AL, Klein RS, Chan JA, Sun Y, Schmidt K, Kieran MW, Luster
AD, Segal RA. A small-molecule antagonist of CXCR4 inhibits intracranial
growth of primary brain tumors. PNAS USA 2003;100(23):13513-8.
16. Kim JY, Nelson AL, Algon SA, Graves O, Sturla LM, Goumnerova LC, Rowitch
DH, Segal RA, Pomeroy SL. Medulloblastoma tumorigenesis diverges from
cerebellar granule cell differentiation in patched heterozygous mice.
Dev Biol 2003;263(1):50-66.
See Dr. Segal's publications via PubMed
Contact Information
E-mail:
Rosalind A. Segal, MD/PhD
Associate Professor of Neurology
Harvard Medical School/Beth Israel
Deaconess Medical Center
