Interactions between neurons and their environment during development
Cell Adhesion Molecules Drive Neuronal Development: Our brains are an amazing network of cells, connected by axons and dendrites that form the conduits for our thoughts and actions. One of the fundamental questions of neuroscience is to understand how these connections form. As such these cells and their processes must differentiate appropriate partners from inappropriate targets. The fidelity with which this happens is truly astounding. Neuroscientists have found that molecules outside the cells instruct all the stages of neural development. For example growth factors secreted from other cells instruct nerve cells to adopt the correct fate, diffusible cues inform neurons where potential synaptic partners might be located and cell surface cues can tell them when they have reached their targets. Work in the Ackley Lab seeks to understand the contribution of cell adhesion molecules to the process of neural development, and we use genetics, cell biology and biochemistry to approach to this problem.
Flamingo is a member of an evolutionarily conserved family of molecules called cadherins. We have found that the C. elegans flamingo member, FMI-1, contributes to the axonal outgrowth and synapse formation of GABAergic motorneurons. We have also found that another conserved cadherin protein, CDH-4, appears to function in the FMI-1 pathway. Little is known about how cadherins interact heterotypically, while much more is known about how they interact homotypically.
2. Calcium-dependent Synapse Formation
Previously we have found that the conserved basement membrane protein, nidogen, and a cell-surface receptor, LAR, function in maintaining the morphology and position of neuromuscular junctions (NMJs) in C. elegans. In a genetic modifier screen we have found that molecules in a calcium signaling pathway, including a voltage gated calcium channel, the calmodulin kinase II (CaMKII) and a conserved calcium binding protein, calmyrin, function in this pathawy. Mutations that ablate the function of the calcium signaling pathway can suppress morphological defects caused by nidogen mutations. In cases where the calcium pathway is hyperactivated they mimic the loss of nidogen. Our lab has recently been using time-lapse confocal micrsocopy to visualize GABAergic NMJs during development, and coupling that with mutations in molecules that regulate their formation.
3. RNAi of Cell Adhesion Molecules
Using a bioinformatic approach we have created a list of all of the genes in the C. elegans genome predicted to be secreted into the extracellular space. This list (The Secretome) includes ~10,000 members. To facilitate understanding how each of these may contribute to development we are creating a library of RNAi clones directed against each member of the list. Ultimately this will provide a valuable rescoure to investigators wanting to probe the contribution of secreted molecules to pathways of interest.
C. elegans as a Model for in vivo Medicinal Probe Development
Beyond their utility as a genetic model organism, C. elegans have vast potential to develop flourescent molecular probes. We collaborate with Dr. Blake Peterson (KU Medicinal Chemistry) to develop, assay and validate molecular probes and their targets. Our research groups were awarded one of the highly competetive NIH Challenge Grants in 2009 to facilitate the start of this project.
- Huarcaya Najarro, E., Wong, L., Zhen, M., Pinedo Carpio, E., Goncharov, A., Garriga, G., Jin, Y., and Ackley, B.D. The C. elegans Flamingo cadherin fmi-1 regulates GABAergic neuronal development. Journal of Neuroscience. 2012;32(12):4196-4211. http://www.ncbi.nlm.nih.gov/pubmed/22442082
- Steimel A, Wong L, Najarro EH, Ackley BD, Garriga G, Hutter H. The Flamingo ortholog FMI-1 controls pioneer-dependent navigation of follower axons in C. elegans. Development. 2010;137(21):3663-73. PMCID: 2959053. http://www.ncbi.nlm.nih.gov/pubmed/20876647
- Grill B, Bienvenut WV, Brown HM, Ackley BD, Quadroni M, Jin Y. C. elegans RPM-1 regulates axon termination and synaptogenesis through the Rab GEF GLO-4 and the Rab GTPase GLO-1. Neuron. 2007;55(4):587-601. http://www.ncbi.nlm.nih.gov/pubmed/17698012
- Gracheva EO, Burdina AO, Holgado AM, Berthelot-Grosjean M, Ackley BD, Hadwiger G, et al. Tomosyn inhibits synaptic vesicle priming in Caenorhabditis elegans. PLoS Biol. 2006;4(8):e261. PMCID: 1514790. http://www.ncbi.nlm.nih.gov/pubmed/16895441
- Dai Y, Taru H, Deken SL, Grill B, Ackley B, Nonet ML, et al. SYD-2 Liprin-alpha organizes presynaptic active zone formation through ELKS. Nat Neurosci. 2006;9(12):1479-87. http://www.ncbi.nlm.nih.gov/pubmed/17115037
- Ackley BD, Harrington RJ, Hudson ML, Williams L, Kenyon CJ, Chisholm AD, et al. The two isoforms of the Caenorhabditis elegans leukocyte-common antigen related receptor tyrosine phosphatase PTP-3 function independently in axon guidance and synapse formation. J Neurosci. 2005;25(33):7517-28. http://www.ncbi.nlm.nih.gov/pubmed/16107639
- Ackley BD, Jin Y. Genetic analysis of synaptic target recognition and assembly. Trends Neurosci. 2004;27(9):540-7. http://www.ncbi.nlm.nih.gov/pubmed/15331236
- Ackley BD, Kang SH, Crew JR, Suh C, Jin Y, Kramer JM. The basement membrane components nidogen and type XVIII collagen regulate organization of neuromuscular junctions in Caenorhabditis elegans. J Neurosci. 2003;23(9):3577-87. http://www.ncbi.nlm.nih.gov/pubmed/12736328
- Kuo CJ, LaMontagne KR, Jr., Garcia-Cardena G, Ackley BD, Kalman D, Park S, et al. Oligomerization-dependent regulation of motility and morphogenesis by the collagen XVIII NC1/endostatin domain. J Cell Biol. 2001;152(6):1233-46. PMCID: 2199214. http://www.ncbi.nlm.nih.gov/pubmed/11257123
- Ackley BD, Crew JR, Elamaa H, Pihlajaniemi T, Kuo CJ, Kramer JM. The NC1/endostatin domain of Caenorhabditis elegans type XVIII collagen affects cell migration and axon guidance. J Cell Biol. 2001;152(6):1219-32. PMCID: 2199198. http://www.ncbi.nlm.nih.gov/pubmed/11257122
- Kramerova IA, Kawaguchi N, Fessler LI, Nelson RE, Chen Y, Kramerov AA, et al. Papilin in development; a pericellular protein with a homology to the ADAMTS metalloproteinases. Development. 2000;127(24):5475-85. http://www.ncbi.nlm.nih.gov/pubmed/11076767
- McCrea M, Kelly JP, Kluge J, Ackley B, Randolph C. Standardized assessment of concussion in football players. Neurology. 1997;48(3):586-8. http://www.ncbi.nlm.nih.gov/pubmed/9065531