Mei Zhen

Degrees: Ph.D. 1995

Affiliations: Lunenfeld-Tanenbaum Research Institute

Courses Taught: JYG155 (Current Topics in Molecular and Cellular Neurobiology); JDB1025H (Developmental Biology); MMG 1012H (Advanced Imaging: Techniques and Application in Biological Systems); Undergraduate ROPs, fourth year thesis advising. 

Research Synopsis

Keywords:   calcium imaging, electrophysiology, motor behaviour, optogenetics, genetics, neural development, machine learning, automated tracking, electron microscopy

Detailed Description: We investigate how neural circuits enable motor behaviors. Using the C. elegans motor circuit as a model, we combine the classic genetics studies, optogenetics, electrophysiology and electron microscopy to answer the following questions: 1) How is the anatomic ensemble of the motor circuit regulated at the molecular and cellular level; 2) How does the C. elegans motor circuit generate rhythmic movement pattern; 3) Do any of the molecular determinants for cholinergic and GABAergic motor neuron development play conserved roles in other nervous systems?

C. elegans is an excellent experimental system for these studies: Its compact and fully sequenced genome, as well as the fast life cycle, allows for the application of powerful forward and reverse genetic tools; The connectivity of its simple nervous system has been deduced by EM reconstructions; the transparency of the animal, and the small number of neurons and synapses allow live imaging at single neuron and single synapse resolution; Physiology tools - in vivo calcium imaging and intracellular recording, are now available, expanding the horizon of functional analyses of nervous system development and function; Lastly, C. elegans exhibits a limited repertoire of motor behaviors that can be precisely quantified through automated tracking systems.

Approaches:
1. In collaboration with the Litchman and Samuel groups (Harvard University), we are using cutting-edge, automated EM technique to reconstruct the wiring of the C. elegans developing nervous system.

2. We developed an array of fluorescent markers that allow us to examine the axon and synapse morphology of C. elegans neurons. We perform genetic screens to identify C. elegans mutants that exhibit defective polarization and synapse morphology. Our subsequent molecular genetic characterization of these mutants leads to the identification of key regulators of neuronal development. 

3. We developed state-of-art movement tracking, electrophysiology, calcium imaging and optogenetics tools to interrogate the functional connectivity of the C. elegans neuromuscular system. Through these tools, we have demonstrated the presence of action potentials in C. elegans body wall muscles, and the role of a small group of premotor interneurons in controlling the directionality of C. elegans’ movement.

4. We are using the C. elegans GABAergic neurons and GABAergic NMJs to model human mental disorders.

METHODS USED

Cell and tissue culture: Neurons.

Procedures: machine learning, automated tracking, behavioural tests, electrophysiology, gene expression analysis, immunohistochemistry, immunocytochemistry, in-vitro electrophysiology, in-vivo electrophysiology, in-vivo calcium imaging, mass spectrometry, optogenetic manipulation, patch clamp, proteomics, qRT-PCR, RT-PCR, siRNA, voltage clamp, western blot

EQUIPMENT USED

Amplifier, analytical balances, benchtop centrifuge, blotting apparatus, calcium imaging system, confocoal microscope, culture hood, culture incubators, deconvolution fluorescence microscope, digital microscope, dissecting microscope, electron microscope, electrophysiology rig, EMCCD, fluorescence microscope, gel apparatus, HPLC, low- and high-speed centrifuge, mass spectrometer, micropipette puller, microwave oven, mini vortexer, stirrer/hot plate, stimulator, water baths.

PRESENT AND RECENT TRAINEES

Leila Lesanpezeshki, PhD, Postdoctoral Fellow (2021-)
Jun Meng, PhD (2015-2021), Postdoctoral Fellow (2021-)
Hongruo Zhang, PhD Candidate (2019-)
Tosif Ahamed, PhD, Postdoctoral Fellow (2019-)
Christine Rehaluk, MSc (2018-2021)
Neeraja Ramakrishnan, PhD Candidate (2018-)
Yangning Lu, PhD (2014-2020)
Ben Mulcahy, PhD, Postdoctoral Fellow (2013-)
Sihui Asuka Guan, MSc (2012-2015)

PRESENT COLLABORATIONS

Within the Department of Physiology:
- Shuzo Sugita, UHN, University of Toronto

Toronto based:
- Gary Bader, CCBR, Department of Molecular Genetics, University of Toronto
- Ben Blencowe, Department of Molecular Genetics, University of Toronto
- John Calarco, Department of Cell and Systems Biology, University of Toronto
- Brent Derry, Department of Molecular Genetics, University of Toronto
- Penney Gilbert, Department of Biomedical Materials and Biomedical Engineering, University of Toronto
- Sonya MacParland, UHN, Department of Immunology, University of Toronto
- Andras Nagy, Institute of Medical Science, University of Toronto
- Kenichi Okamoto, LTRI, Department of Molecular Genetics, University of Toronto
- Jeehye Park, The Hospital for Sick Children, Department of Molecular Genetics, University of Toronto​

International:
- Andrew Chisholm, Department of Biology, University of California San Diego
- Christopher Fang-Yen, University of Pennsylvania
- Shangbang Gao, Department of Life Sciences, Huazhong University of Science and Technology, China
- Brock Grill, Department of Neuroscience, Scripps Research
- Xun Huang, Institute of Genetics, Chinese Academy of Sciences
- Yishi Jin, University of California San Diego
- Jeff Lichtman, The Center for Brain Science, Harvard University
- Alan Mullen, Harvard Medical School / Massachusetts General Hospital
- Aravinthan DT Samuel, The Center for Brain Science, Physics Department, Harvard University
- Paul Sternberg, California Institute of Technology
- Christian Stigloher, Department of Biology, University of Wurzburg, Germany
- Vivek Venkatachalam, Northeastern University

Recent Publications

Witvliet D, Mulcahy B, Mitchell JM, Meirovitch Y, Berger DR, Wu Y, Liu Y, Koh WR, Parvathala R, Holmyard D, Schalek RL, Shavit N, Chisholm AD, Lichtman JW, Samuel ADT, and Zhen M. (2021) Connectomes across development reveal principles of brain maturation. Nature 596:257-261

Dong XK, Kheiri K, Lu YN, Xu ZY, Zhen M, Liu XY. Towards a live soft microrobot: optogenetic locomotion control of Caenorhabditis elegans. Science Robotics 6(55): eabe3950

Susoy V, Hung W, Witvliet D, Whitener JE, Wu M, Graham BJ, Zhen M, Venkatachalam V, Samuel ADT. Natural sensory context drives diverse brain-wide activity during C. elegans mating. Cell 184(20): 5122-5137.e17 A

Britz S, Markert SM, Witvliet D, Steyer AM, Tröger S, Mulcahy B, Kollmannsberger P, Schwab Y, Zhen M, Stigloher C. Structural analysis of the C. elegans dauer larval anterior sensilla by Focused Ion Beam-Scanning Electron Microscopy. Frontiers In Neuroanatomy. 15:732520

Wang Z, Zhu L, Zhang H, Li G, Yi C, Li Y, Yang Y, Ding Y, Zhen M, Gao S, Hsiai TK, Fei P. Real-time volumetric reconstruction of biological dynamics with light-field microscopy and deep learning. Nature Methods 18: 551-556

Appointments

Primary: Molecular Genetics & Microbiology