Mechanisms of synaptic competition at developing neuromuscular synapses
We are studying the mechanisms underlying synaptic competition during neural development, using neuromuscular synapses as a model system. Using transgenic mice in which the dynamics of synaptic vesicle recycling and trafficking can be monitored in vivo, we are testing the hypothesis that activity modulates presynaptic vesicle recycling and trafficking, affecting synaptic structure, strength and survival.The results of these experiments will provide fundamentally new insights into mechanisms by which activity changes synaptic function and neural circuitry during normal development, and contribute to understanding of developmental disorders such as epilepsy, autism and mental retardation. Click here for more details.
Mechanisms of neuron-astrocyte signaling underlying synapse formation and function
We are studying the mechanisms by which astrocytes modulate inhibitory synapse formation and function in the developing central nervous system. Previous work and preliminary studies in hippocampal neurons in vitro suggest that astrocytes release soluble signals into the media (astrocyte conditioned media, ACM) that increase inhibitory neuron axon elongation, branching as well as synaptogenesis, by the criteria of increasing the number of GABAergic presynaptic terminals colocalized with postsynaptic GABAAR clusters (Elmariah et al., 2004; 2005; Hughes et al., 2010). These data lead to the hypothesis that secreted signals from astrocytes mediate the formationn of inhibitory synapses during neural development. The results of these experiments will extend our understanding of how inhibitory synapses are formed during neural development, and may also contribute to understanding of disorders of development such as epilepsy, autism and mental retardation. Click here for more details.
Related collaborative projects
Novel forms of encephalitis was recently identified by Dr. Josep Dalmau in the Dept. of Neurology, Hospital Clinic and University of Barcelona, Spain. These diseases are associated with antibodies to the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptor, the GluR1 / GluR2 subunits of the AMPA receptor, among several other cell surface proteins. These disorders were initially identified in young women with ovarian teratoma who presented with psychosis or memory problems that evolved to severe complications requiring prolonged intensive care support. Prompt recognition of this disorder is important because patients often improve with treatment.
With Dr. Dalmau and his lab, we are working to study the binding of patients’ antibodies to NMDA or AMPA receptor clusters at synapses formed in cultures of rodent hippocampal neurons. We are also determining how cerebrospinal fluid from affected patients affects synapse structure and function, how NMDA receptors are cleared from synapses, and whether these affects are reversible. Collaborative efforts are underway to generate and characterize animal models of this human disease.
Zebrafish have become increasingly popular for studying blood cell development because many zebrafish orthologs of blood-specific genes have been identified, and the rapid, external development of abundant, transparent embryos enables real-time functional observations unlike other models. Moreover, transgenic zebrafish models of other leukemias have yielded phenotypes that recapitulate leukemia in humans. In collaboration with Dr. Carolyn Felix's lab at CHOP, we are using zebrafish model to understand the role of the human mll gene in normal and malignant hematopoiesis. The mll gene at chromosome band 11q23 is an important oncogene that is disrupted by chromosomal translocations with more than 50 partner genes in infant leukemias and secondary leukemias after chemotherapeutic topoisomerase II poisons. The functions of MLL in normal blood cell development and leukemia are poorly understood. Mll encodes a complex transcription factor that undergoes taspase1 proteolytic cleavage into amino and carboxyl fragments that re-associate in a multiprotein complex and regulate expression of HOX genes, cell cycle genes and other unknown targets. Experiments in mice indicate that MLL is important for normal hematopoiesis and that disruption of MLL function is leukemogenic. We have cloned a complete zebrafish mll cDNA, and have shown that mll depletion in zebrafish embryos leads to blood cell defects and neuronal cell death, resembling phenotypes observed in Mll-/- mice. Understanding the role of mll in hematopoeisis in zebrafish as a model system will provide a rapid screening tool to test anti-leukemic agents targeting MLL fusion proteins or their downstream effectors.
The Neuronal Ceroid-Lipofuscinoses (NCLs) are the most common recessively inherited neurodegenerative disorders in man, with a combined incidence of around one in 12,5001. NCL patients have progressive visual loss due to retinal pigment degeneration, seizures, loss of motor function leading to spastic quadriplegia, and cognitive defects culminating in a vegetative state and early death3. Autopsied brains of CLN3 patients are reduced in size due to massive but specific neuronal death4. While the pathways leading to neuronal loss have not been elucidated, apoptosis is triggered by abnormal intracellular calcium signaling and occurs through the caspase pathway5,6. Presently, nine genotypes for the NCLs have been described with overlapping neural and metabolic phenotypes. The juvenile form of NCL (JNCL, Batten or Spielmeyer-Vogt-Sjogren disease, CLN3) results from mutations in the CLN3 gene on chromosome 162. A common 1.02 kb deletion of exons 7 and 8 accounts for the majority of CLN3 patient alleles. CLN3 is a 48 KDa integral membrane protein associated with membrane lipid rafts that functions as a palmitoyl-protein desaturase enzyme with as yet unknown substrates. How disregulated protein palmitoylation leads to prominent cell death in the CNS is unknown. In collaboration with Dr. Michael Bennett's laboratory at CHOP, we are developing a zebrafish model of NCL. While mouse models of JNCL/CLN3 exist, the availability of a zebrafish model would enable studies of the effects of CLN3 deletion in the CNS, disease onset and progression, allow genetic interaction studies to identify the pathways affected by CLN3, in particular why mutations in so many diverse genes cause grossly similar NCL phenotypes, and facilitate screening of small molecules and drugs as potential therapeutic agents. Preliminary studies have shown that knockdown of CLN3 with 3 different morpholinos causes specific patterns of cell death in the CNS that are similar to those seen in CLN3 mutant mice.
The lab usually has one or more rotation students from the Neuroscience, CAMB, Biology and other graduate groups per semester. Prospective rotation students meet with Dr. Balice-Gordon to get an overview of current work, then meet with grad students and postdocs to learn more about projects of particular interest. Rotation students typically work closely with a lab member.
Isaac Perron, NGG - Characterization of astrocyte truncated TrkB in synaptic plasticity related to sleep (collaborative project with Dr. Marcos Frank).