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Christine Holt FRS FMedSci

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Professor of Developmental Neuroscience
Tel: +44 (0)1223 766229, Fax: +44 (0)1223 333786/840, E-mail: ceh33@cam.ac.uk

Wiring the brain: axon guidance and synaptic specificity

We are investigating how axons are guided to their correct synaptic targets in the brain. In the developing vertebrate visual system, retinal ganglion cells in the eye extend axons that navigate over a long distance to their synaptic targets in the midbrain. This impressive navigational feat underlies the precise wiring of the mature brain and is essential for building functional nerve connections. The goal of our research is to understand the molecular and cellular mechanisms that guide axon growth. We use a multidisciplinary experimental approach that involves in vivo gene transfer, growth cone turning assays in vitro and time-lapse imaging of live axons in the brain. We focus in particular on the steering points within the visual pathway where axons alter their direction of growth and/or their behaviour such as the optic disc, the optic chiasm and the site of target entry. We have found, for example, that ephrin-B is important in regulating the divergent routing of axons at the chiasm and that netrin-1/DCC/laminin-1 interactions play a key role in directing axons out of the eye. Our studies have also revealed that the growing tips of axons, the growth cones, rapidly synthesize new proteins in response to encounters with guidance cues such as netrin-1. Inhibition of this local protein synthesis blocks the turning responses of growth cones in a chemotropic gradient suggesting that local translation of mRNAs is involved in directional steering. By understanding the molecular and cellular mechanisms that guide axon growth in development we aim to understand how nerve connections are first established. Basic knowledge of this sort is essential for the development of clinical therapies in nerve repair and for understanding neurodevelopmental disorders.

A short movie depicting in vivo time-lapse imaging of retinotectal axon pathfinding in Xenopus laevis can be viewed below.

Colleagues
Hanna Hornberg (PhD Student)
Trina Bo Lu (PhD Student)
Claudio Roque (PhD Student)
Vasja Urbancic (PhD Student)
Hovy Wong (PhD Student)
Hosung Jung (Postdoctoral Fellow)
Cathy O’Hare (Postdoctoral Fellow)
Anais Bellon (Postdoctoral Fellow)
Phillip Konopacki (Postdoctoral Fellow)
Kalin Vasilev (Postdoctoral Fellow)
Asha Dwivedy (Research Associate)
Nikki Coutts (Research Assistant)
Thomasz Dyl (Research Technician)
Adrian McNabb (Research Technician)

Main collaborators
Bill Harris (PDN, Cambridge University)
Kristian Franze and Jochen Guck (PDN and Physics, Cambridge)
James Fawcett (Brain Repair Centre, Cambridge)
Eric Miska (Gurdon Institute)

Main sources of funding: Wellcome Trust, HFSP, BBSRC, Gates Foundation Cambridge Trusts.

Selected publications
Leung LC, Urbancic V, Baudet ML, Dwivedy A, Bayley TG, Lee AC, Harris WA, Holt CE. Coupling of NF-protocadherin signaling to axon guidance by cue-induced translation. Nature Neurosci 16:166-73 (2012).

Jung H, Yoon BC, Holt CE. Axonal mRNA localization and local protein synthesis in nervous system assembly, maintenance and repair. Nature Reviews Neuroscience 13:308-24 (2012).

Yoon BC, H Jung, A Dwivedy, CM O’Hare, KH Zivraj and CE Holt. Local translation of extranuclear lamin B promotes axon maintenance. Cell 148:752-64 (2012).

Baudet, M-L, K Zivraj, C Abreu-Goodger, A Muldal, J Armisen, C Blenkiron, LD Goldstein, EA Miska and CE Holt. miR-124 acts via CoREST to control onset of Sema3A sensitivity in navigating retinal growth cones. Nature Neuroscience 15:2-38 (2011).

Jung H, O'Hare CM, Holt CE. Translational regulation in growth cones. Curr Opin Genet Dev 21:458-64 (2011).

Gumy LF, GSH Yeo, Y-CL Tung, K Zivraj, D Willis, G Coppola, BYH Lam, JL Twiss, CE Holt and JW Fawcett. Global transcriptome analysis reveals differences between embryonic and adult dorsal root ganglion axonal mRNAs that are implicated in axonal growth and pain. RNA 17:85-98 (2011).

Jung, H and CE Holt. Local translation of mRNAs in neural development. WIREs RNA Vol 1 (2010).

Zivraj, K. L. Tung, M. Piper, L. Gumy, J. Fawcett, G. Yeo, and CE. Holt. Subcellular profiling reveals distinct and developmentally regulated repertoire of growth cone mRNAs. J Neurosci 30:15464-78 (2010).

Drinjakovic J, H. Jung, DS Campbell, L Strochlic and CE Holt. E3 ligase Nedd4 promotes axon branching by down-regulating PTEN. Neuron 65:341-57 (2010).

Holt, CE and S. Bullock. Subcellular mRNA Localization in Animal Cells and Why it Matters. Science 326:1212-6 (2009).

Wizenmann et al. Extracellular Engrailed participates in the topographic guidance of retinal axons in vivo. Neuron 12:355-66 (2009).

Lin AC, CL Tan, C-L Lin, L Strochlic, Y-S Huang, JD Richter, CE Holt. Cytoplasmic polyadenylation and CPE-dependent mRNA regulation are involved in Xenopus retinal axon development. Neural Development 4:8 (2009).

Leung, K-M. and CE Holt. Live visualization of protein synthesis in axonal growth cones by microinjection of photoconvertible Kaede into Xenopus embryos. Nature Protocols 3:1318-27 (2008).

Piper M, A Dwivedy, L Leung, RS Bradley and CE Holt. NF-protocadherin and TAF1 regulate retinal axon initiation and elongation in vivo. J Neurosci 28:100-5 (2008).

Lin AC and CE Holt. Local translation and directional steering in axons. MiniReview. EMBO J 26:3729-36 (2007).

Leung, K-M., van Horck, FPG, Andrew C Lin, Allison, R., Standart, N. and Holt, CE. Asymmetrical b-actin mRNA translation in growth cones mediates attractive turning to netrin-1. Nature Neuroscience 9:1247-56 (2006).

Piper. M., R. Anderson, A. Dwivedy, C. Weinl, F. van Horck, K-M. Leung, E. Cogill and C. Holt. Signaling mechanisms underlying Slit2-induced collapse of Xenopus retinal growth cones. Neuron 49:215-28 (2006).

Brunet I., C. Weinl, M. Piper, A. Trembleau, M. Volovitch, W.A. Harris, A. Prochiantz, C.E. Holt. The transcription factor Engrailed-2 guides retinal axons. Nature 438:94-98 (2005).

Piper, M., S. Salih, C. Weinl, C.E. Holt and W. A. Harris. Endocytosis-dependent desensitization and protein synthesis-dependent resensitization in retinal growth cone adaptation. Nature Neuroscience 8:179-86 (2005).

Piper, M. and C.E. Holt. RNA Translation in Axons. Annual Review of Cell and Developmental Biology 20:505-23 (2004).

Shewan, D.S., A. Dwivedy, R. Anderson and C.E. Holt. Age-related changes underlie switch in netrin-1 responsiveness as growth cones advance along visual pathway. Nature Neuroscience 5:955-62 (2002).

Mann F, Ray, S., Harris, W.A. and Holt, C.E. Topographic mapping in dorsoventral axis of the Xenopus retinotectal system depends on signalling through ephrin-B ligands. Neuron 35:461-73 (2002).

Campbell, D.S. and C.E. Holt. Chemotropic responses of retinal growth cones mediated by rapid local protein synthesis and degradation. Neuron 32:1013-26 (2001).

Nakagawa, S-i., C. Brennan, K. Johnson, D. Shewan, W.A. Harris and C.E. Holt. Ephrin-B regulates the ipsilateral routing of retinal axons at the optic chiasm. Neuron 25:599-610 (2000).

Hoepker, V.H., D. Shewan, M. Tessier-Lavigne, M-m. Poo and C.E. Holt Growth cone attraction to netrin-1 is converted to repulsion by laminin-1. Nature 401:69-73 (1999).

Image

Above: Growth cone of retinal ganglion cell axon showing asymmetrical distribution of beta-actin after exposure to a 5 minute gradient of netrin-1 (top right). This spatial asymmetry is generated by local translation of beta-actin mRNA and is critical for attractive turning towards netrin-1 (see Leung et al, 2006).


image

Above: Single retinal ganglion cell in the embryonic visual system. The cell is stained with a dye (HRP) to reveal its soma and developing dendrites in the eye and its long axon extending across the midline (optic chiasm) into the contralateral optic tract. It is tipped with a motile growth process, the growth cone, which responds to guidance cues along the pathway and leads the axon to its final destination in the midbrain.


Quicktime Movie: in vivo timelapse imaging of retinotectal axon pathfinding in Xenopus laevis: