B.S. Biology; MIT, Cambridge MA; 1979
Ph.D. Biochemistry; Stanford Univ. Medical School, Stanford CA; 1986
Postdoctoral: Neuroscience, Massachusetts General Hospital; Boston, MA. 1986-1988
Postdoctoral: Molecular Neuroscience, Dana Farber Cancer Inst.; Boston, MA. 1988-1991
Research Interests, Dr. Alfred Geller
We are studying the encoding of an advanced cognitive task, visual object discrimination learning, using a genetic approach for neuronal circuit analysis. This learning is encoded in a distributed rat neocortical circuit that spans a critical multimodal associative area, postrhinal (POR) cortex, which is required for this learning. POR cortex neurons receive afferents from specific visual areas, and project to more than ten neocortical areas.
The genetic intervention we are using is activation of protein kinase C (PKC) pathways in small numbers of spatially localized neurons, via a virus vector. Specific PKC genes are required for specific learning tasks. Further, constitutively active PKCs occur naturally from calpain cleavage, and constitutively active PKMz is genetically encoded, although it is not required for learning. Our approach is that activating PKC pathways affects plasticity to enhance learning, consistent with known roles of PKCs. The hypothesis is that neurons that contain activated PKC pathways increase their response to incoming activity representing a specific discrimination, thereby enhancing learning.
We showed that genetically modifying several hundred neurons in the critical multimodal associative area, POR cortex, alters synaptic plasticity and enhances visual learning. We delivered a constitutively active PKC (via a virus vector) into several hundred spatially-grouped glutamatergic and GABAergic neurons in POR cortex. This intervention activates PKC pathways and increases activation-dependent neurotransmitter release. Of note, the rats learn new visual object discriminations faster and to higher accuracy, but performance is not altered on control discriminations learned before gene transfer.
Importantly, some of the essential information for performance is encoded in the genetically-modified circuit. After both the gene transfer and learning, creation of small neurochemical lesions that ablate the genetically-modified circuit (~21 % of POR cortex) selectively reduces performance for only discriminations learned after gene transfer.
During learning, the genetically-modified circuit is preferentially activated. Activity-dependent gene imaging showed that before learning, this circuit exhibits minimal activity; the constitutively active PKC, alone, does not increase activity. Visual learning increases activity throughout POR cortex, and, importantly, the genetically-modified circuit exhibits larger increases in activity, but only during performance of discriminations learned after gene transfer. This critical circuit contains ~500 neurons and is sparse-coded, with a coding density of ~3 %.
Specific discriminations are encoded in characteristic and different neuronal ensembles, and different discriminations are encoded in intermingled ensembles, as shown by mapping the positions of the active neurons in the critical circuit.
An identified ensemble in the circuit, the transduced neurons, is required for both learning and subsequent performance. To show activity in the transduced neurons is required for learning, PKC pathways were activated and neurotransmitter release was blocked, by coexpressing a Synaptotagmin I (Syt I) siRNA. To show activity in the transduced neurons is required for performance, after gene transfer and learning, Syt I siRNA expression was induced from a regulated promoter, resulting in deficits in performance. Correlatively, during learning, dendritic protein synthesis and three learning-associated signaling pathways; CaMKII, MAP kinase, and CREB; are preferentially activated in the transduced neurons.
We are currently determining the relationship between the gain in the circuit and learning, a critical parameter that controls learning in neural network theory. To this end, we are genetically modifying the action potential-dependent gain in neurotransmitter release during the learning. The results show that learning can occur only within a narrow range of the gain in release.
These results establish approaches for analyzing the encoding mechanisms and mapping the critical circuit. First, we will analyze encoding mechanisms by activating PKC pathways and coexpressing a gene that alters synaptic plasticity. Second, we will identify the neuron and synapse types that encode the learning. Using gene transfer to connected neurons, detailed below, the presynaptic neurons will receive the genetic modification that enhances learning, and, after learning, specific postsynaptic neuron types will receive a gene that blocks neuronal activity. Inhibiting critical postsynaptic neurons will cause learning deficits, identifying critical components. Third, for the critical ensembles, we will detail network architecture, which constrains encoding, and distinguish between physical synapses, physiological connections, and essential circuits. We will use modern genetic tools to map the critical neurons and synapses.
For over two decades, my laboratory has pioneered helper virus-free Herpes Simplex Virus (HSV-1) vectors for gene tranfer into neurons. We were responsible for the first direct gene transfer into neurons using a virus vector, the first use of a virus vector to alter neuronal physiology, and the first use of direct gene transfer to correct an animal model of a neurological disease. Further, we were responsible for the first temperature sensitive mutant packaging system, the first deletion mutant packaging system, and the first helper virus-free packaging system.
After developing the vector system, we realized that due to the complexity of the mammalian brain, a number of additional technological capabilities were essential for analyzing circuits. First, we developed promoters that support long-term expression in all neurons, or specific neuron types, including catecholaminergic, GABAergic, glutamatergic, or glutamatergic neuron subtypes. Second, we developed a general method to target gene transfer to specific neuron types, antibody-mediated targeting. We added the Staphylococcus A protein antibody binding domain to a vector particle protein. Complexes of these vector particles and specific antibodies target gene transfer to specific neuron types, such as neurons that contain NMDA receptor NR2A or 2B subunits. Third, we developed targeted gene transfer to deliver different genes into presynaptic neurons and a selected subset of their postsynaptic neurons, based on both projection area and synapse type, such as glutamatergic. The first gene transfer, into the presynaptic neurons, uses standard procedures. The vector expresses an artificial peptide neurotransmitter that contains a dense core vesicle sorting domain, a neurotransmitter receptor binding domain, and the His tag. Upon release, this peptide neurotransmitter binds to the cognate receptors on the postsynaptic neurons. Antibody-mediated targeting to these postsynaptic neurons uses a His tag antibody, as the peptide neurotransmitter contains the His tag. Fourth, we recently developed HSV-Brainbow, which can label small numbers of neurons with unique hues. Additional technologies for circuit analysis will be developed, as indicated by results.
Geller AI, Rich A. A UGA termination suppression tRNATrp active in rabbit reticulocytes. Nature 1980;283:41-6.
Geller AI, Breakefield XO. A defective HSV-1 vector expresses Escherichia coli beta-galactosidase in cultured peripheral neurons. Science 1988;241:1667-9.
Geller AI, Keyomarsi K, Bryan J, Pardee AB. An efficient deletion mutant packaging system for defective herpes simplex virus vectors: potential applications to human gene therapy and neuronal physiology. Proc Natl Acad Sci USA 1990;87:8950-4.
Geller AI, Freese A. Infection of cultured central nervous system neurons with a defective herpes simplex virus 1 vector results in stable expression of Escherichia coli beta-galactosidase. Proc Natl Acad Sci USA 1990;87:1149-53.
Federoff HJ, Geschwind MD, Geller AI, Kessler JA. Expression of nerve growth factor in vivo from a defective herpes simplex virus 1 vector prevents effects of axotomy on sympathetic ganglia. Proc Natl Acad Sci USA 1992;89:1636-40.
Battleman DS, Geller AI, Chao MV. HSV-1 vector-mediated gene transfer of the human nerve growth factor receptor p75hNGFR defines high-affinity NGF binding. J Neurosci 1993;13:941-51.
Geller AI, During MJ, Haycock JW, Freese A, Neve R. Long-term increases in neurotransmitter release from neuronal cells expressing a constitutively active adenylate cyclase from a herpes simplex virus type 1 vector. Proc Natl Acad Sci USA 1993;90:7603-7.
During MJ, Naegele JR, O'Malley KL, Geller AI. Long-term behavioral recovery in parkinsonian rats by an HSV vector expressing tyrosine hydroxylase. Science 1994;266:1399-403.
Fraefel C, Song S, Lim F, Lang P, Yu L, Wang Y, Wild P, Geller AI. Helper virus-free transfer of herpes simplex virus type 1 plasmid vectors into neural cells. J Virol 1996;70:7190-7.
Song S, Wang Y, Bak SY, Lang P, Ullrey D, Neve RL, O'Malley KL, Geller AI. An HSV-1 vector containing the rat tyrosine hydroxylase promoter enhances both long-term and cell type-specific expression in the midbrain. J Neurochem 1997;68:1792-803.
Song S, Wang Y, Bak SY, During MJ, Bryan J, Ashe O, Ullrey DB, Trask LE, Grant FD, O'Malley KL, Riedel H, Goldstein DS, Neve KA, LaHoste GJ, Marshall JF, Haycock JW, Neve RL, Geller AI. Modulation of rat rotational behavior by direct gene transfer of constitutively active protein kinase C into nigrostriatal neurons. J Neurosci 1998;18:4119-32.
Zhang G, Wang X, Yang T, Sun M, Zhang W, Wang Y, Geller AI. A tyrosine hydroxylase--neurofilament chimeric promoter enhances long-term expression in rat forebrain neurons from helper virus-free HSV-1 vectors. Molec Brain Res 2000;84:17-31.
Neill JC, Sarkisian MR, Wang Y, Liu Z, Yu L, Tandon P, Zhang G, Holmes GL, Geller AI. Enhanced auditory reversal learning by genetic activation of protein kinase C in small groups of rat hippocampal neurons. Molec Brain Res 2001;93:127-36.
Sun M, Zhang G, Kong L, Holmes C, Wang X, Zhang W, Goldstein DS, Geller AI. Correction of a rat model of Parkinson’s disease by coexpression of tyrosine hydroxylase and aromatic amino acid decarboxylase from a helper virus-free herpes simplex virus type 1 vector. Hum Gene Ther 2003;14:415-24.
Cook RG, Geller AI, Zhang G, Gowda R. Touchscreen enhanced visual learning in rats. Behav Res Methods Instrum Comput 2004;36:101-6.
Sun M, Kong L, Wang X, Holmes C, Gao Q, Zhang W, Pfeilschifter J, Goldstein DS, Geller AI. Coexpression of Tyrosine Hydroxylase, GTP Cyclohydrolase I, Aromatic Amino Acid Decarboxylase, and Vesicular Monoamine Transporter-2 from a Helper Virus-Free HSV-1 Vector Supports High-Level, Long-Term Biochemical and Behavioral Correction of a Rat Model of Parkinson’s Disease. Hum Gene Ther 2004;15:1177-1196.
Wang X, Kong L, Zhang G, Sun M, Geller AI. Targeted gene transfer to nigrostriatal neurons in the rat brain by helper virus-free HSV-1 vector particles that contain either a chimeric HSV-1 glycoprotein C--GDNF or a gC--BDNF protein. Molec Brain Res 2005;139:88-102.
Sun M, Kong L, Wang X, Lu X, Gao Q, Geller AI. Comparison of protection of nigrostriatal neurons by expression of GDNF, BDNF, or both neurotrophic factors. Brain Res 2005;1052:119-29.
Zhang G, Wang X, Kong L, Lu X, Lee B, Liu M, Sun M, Franklin C, Cook RG, Geller AI. Genetic enhancement of visual learning by activation of protein kinase C pathways in small groups of rat cortical neurons. Journal of Neuroscience, 2005;25:8468-81.
Gao, Q., Sun, M., Wang, X., Zhang, G., and Geller, A.I. Inducible long-term expression in striatal neurons from helper virus-free HSV-1 vectors containing the tet promoter system. Brain Res., 2006;1083:1-13.
Rasmussen M, Kong L, Zhang G, Liu M, Wang X, Szabo G, Curthoys NP, Geller AI. Glutamatergic or GABAergic neuron-specific, long-term expression in neocortical neurons from helper virus-free HSV-1 vectors containing the phosphate-activated glutaminase, vesicular glutamate transporter-1, or glutamic acid decarboxylase promoter. Brain Res 2007;1144:19-32.
Zhang G, Liu M, Cao H, Kong L, Wang X, Cook RG, Geller AI. Improved spatial learning in aged rats by activation of PKC in small groups of rat hippocampal neurons. Hippocampus 2009;19:413-423.
Cao H, Zhang G, Geller AI. Antibody-mediated targeted gene transfer to NMDA NR1-containing neurons in rat neocortex by helper virus-free HSV-1 vector particles containing a chimeric HSV-1 glycoprotein C--Staphylococcus A protein. Brain Res 2010;1351:1-12.
Zhang G, Geller AI. A helper virus-free HSV-1 vector containing the vesicular glutamate transporter-1 promoter supports expression preferentially in VGLUT1-containing glutamatergic neurons. Brain Res 2010;1331:12-19.
Zhang G, Cao H, Kong L, O’Brien J, Baughns A, Jan M, Zhao H, Wang X, Lu X, Cook RG, Geller AI. Identified circuit in rat postrhinal cortex encodes essential information for performing specific visual shape discriminations. Proc Natl Acad Sci USA 2010;107:14478–14483.
Zhang G, Li X, Cao H, Zhao H, Geller AI. The vesicular glutamate transporter-1 upstream promoter and first intron each support glutamatergic-specific expression in rat postrhinal cortex. Brain Res 2011;1377:1-12.
Cao H, Zhang G, Geller AI. Antibody-mediated targeted gene transfer to NMDA NR2A- or NR2B-containing neurons in rat neocortex by helper virus-free HSV-1 vector particles. Brain Res 2011;1415:127-135.
Zhang G, Zhao H, Cao H, Li X, Geller AI. Targeted gene transfer of different genes to presynaptic and postsynaptic neocortical neurons connected by a glutamatergic synapse. Brain Res 2012;1473:173-184.
Zhang G, Zhao H, Choi EM, Svestka M, Wang X, Cook RG, Geller AI. CaMKII, MAPK, and CREB are coactivated in identified neurons in a neocortical circuit required for performing visual shape discriminations. Hippocampus 2012;22:2276-2289.
Zhang G, Zhao H, Cao H, Li X, and Geller AI. Neurons can be labeled with unique hues by helper virus-free HSV-1 vectors expressing Brainbow. Journal of Neuroscience Methods 2015;240:77-88.